ECMA-262, 15th edition, June 2024
ECMAScript® 2024 Language Specification
About this Specification
The document athttps://tc39.es/ecma262/ is the most accurate and up-to-date ECMAScript specification. It contains the content of the most recent yearly snapshot plus anyfinished proposals (those that have reached Stage 4 in theproposal process and thus are implemented in several implementations and will be in the next practical revision) since that snapshot was taken.
This document is available asa single page and asmultiple pages.
Contributing to this Specification
This specification is developed on GitHub with the help of the ECMAScript community. There are a number of ways to contribute to the development of this specification:
- GitHub Repository:https://github.com/tc39/ecma262
- Issues:All Issues,File a New Issue
- Pull Requests:All Pull Requests,Create a New Pull Request
- Test Suite:Test262
- Editors:
- Community:
- Discourse:https://es.discourse.group
- Chat:Matrix
- Mailing
List Archives:https://esdiscuss.org/
Refer to the
Introduction
This Ecma Standard defines the ECMAScript 2024 Language. It is the fifteenth edition of the ECMAScript Language Specification. Since publication of the first edition in 1997, ECMAScript has grown to be one of the world's most widely used general-purpose programming languages. It is best known as the language embedded in web browsers but has also been widely adopted for server and embedded applications.
ECMAScript is based on several originating technologies, the most well-known being JavaScript (Netscape) and JScript (Microsoft). The language was invented by Brendan Eich at Netscape and first appeared in that company's Navigator 2.0 browser. It has appeared in all subsequent browsers from Netscape and in all browsers from Microsoft starting with Internet Explorer 3.0.
The development of the ECMAScript Language Specification started in November 1996. The first edition of this Ecma Standard was adopted by the Ecma General Assembly of June 1997.
That Ecma Standard was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262, in April 1998. The Ecma General Assembly of June 1998 approved the second edition of ECMA-262 to keep it fully aligned with ISO/IEC 16262. Changes between the first and the second edition are editorial in nature.
The third edition of the Standard introduced powerful regular expressions, better string handling, new control statements, try/catch exception handling, tighter definition of errors, formatting for numeric output and minor changes in anticipation of future language growth. The third edition of the ECMAScript standard was adopted by the Ecma General Assembly of December 1999 and published as ISO/IEC 16262:2002 in June 2002.
After publication of the third edition, ECMAScript achieved massive adoption in conjunction with the World Wide Web where it has become the programming language that is supported by essentially all web browsers. Significant work was done to develop a fourth edition of ECMAScript. However, that work was not completed and not published as the fourth edition of ECMAScript but some of it was incorporated into the development of the sixth edition.
The fifth edition of ECMAScript (published as ECMA-262 5th edition) codified de facto interpretations of the language specification that have become common among browser implementations and added support for new features that had emerged since the publication of the third edition. Such features include
The fifth edition was submitted to ISO/IEC JTC 1 for adoption under the fast-track procedure, and approved as international standard ISO/IEC 16262:2011. Edition 5.1 of the ECMAScript Standard incorporated minor corrections and is the same text as ISO/IEC 16262:2011. The 5.1 Edition was adopted by the Ecma General Assembly of June 2011.
Focused development of the sixth edition started in 2009, as the fifth edition was being prepared for publication. However, this was preceded by significant experimentation and language enhancement design efforts dating to the publication of the third edition in 1999. In a very real sense, the completion of the sixth edition is the culmination of a fifteen year effort. The goals for this edition included providing better support for large applications, library creation, and for use of ECMAScript as a compilation target for other languages. Some of its major enhancements included modules, class declarations, lexical block scoping, iterators and generators, promises for asynchronous programming, destructuring patterns, and proper tail calls. The ECMAScript library of built-ins was expanded to support additional data abstractions including maps, sets, and arrays of binary numeric values as well as additional support for Unicode supplementary characters in strings and regular expressions. The built-ins were also made extensible via subclassing. The sixth edition provides the foundation for regular, incremental language and library enhancements. The sixth edition was adopted by the General Assembly of June 2015.
ECMAScript 2016 was the first ECMAScript edition released under Ecma TC39's new yearly release cadence and open development process. A plain-text source document was built from the ECMAScript 2015 source document to serve as the base for further development entirely on GitHub. Over the year of this standard's development, hundreds of pull requests and issues were filed representing thousands of bug fixes, editorial fixes and other improvements. Additionally, numerous software tools were developed to aid in this effort including Ecmarkup, Ecmarkdown, and Grammarkdown. ES2016 also included support for a new exponentiation operator and adds a new method toArray.prototype calledincludes.
ECMAScript 2017 introduced Async Functions, Shared Memory, and Atomics along with smaller language and library enhancements, bug fixes, and editorial updates. Async functions improve the asynchronous programming experience by providing syntax for promise-returning functions. Shared Memory and Atomics introduce a newObject.values,Object.entries, andObject.getOwnPropertyDescriptors.
ECMAScript 2018 introduced support for asynchronous iteration via the AsyncIterator protocol and async generators. It also included four new regular expression features: thedotAll flag, named capture groups, Unicode property escapes, and look-behind assertions. Lastly it included object rest and spread properties.
ECMAScript 2019 introduced a few new built-in functions:flat andflatMap onArray.prototype for flattening arrays,Object.fromEntries for directly turning the return value ofObject.entries into a new Object, andtrimStart andtrimEnd onString.prototype as better-named alternatives to the widely implemented but non-standardString.prototype.trimLeft andtrimRight built-ins. In addition, it included a few minor updates to syntax and semantics. Updated syntax included optional catch binding parameters and allowing U+2028 (LINE SEPARATOR) and U+2029 (PARAGRAPH SEPARATOR) in string literals to align with JSON. Other updates included requiring thatArray.prototype.sort be a stable sort, requiring thatJSON.stringify return well-formed UTF-8 regardless of input, and clarifyingFunction.prototype.toString by requiring that it either return the corresponding original source text or a standard placeholder.
ECMAScript 2020, the 11th edition, introduced thematchAll method for Strings, to produce an iterator for all match objects generated by a global regular expression;import(), a syntax to asynchronously import Modules with a dynamic specifier;BigInt, a new number primitive for working with arbitrary precisionPromise.allSettled, a new Promise combinator that does not short-circuit;globalThis, a universal way to access the globalthis value; dedicatedexport * as ns from 'module' syntax for use within modules; increased standardization offor-in enumeration order;import.meta, a
ECMAScript 2021, the 12th edition, introduced thereplaceAll method for Strings;Promise.any, a Promise combinator that short-circuits when an input value is fulfilled;AggregateError, a new Error type to represent multiple errors at once; logical assignment operators (??=,&&=,||=);WeakRef, for referring to a target object without preserving it from garbage collection, andFinalizationRegistry, to manage registration and unregistration of cleanup operations performed when target objects are garbage collected; separators for numeric literals (1_000); andArray.prototype.sort was made more precise, reducing the amount of cases that result in an
ECMAScript 2022, the 13th edition, introduced top-levelawait, allowing the#x in obj syntax, to test for presence of private fields on objects; regular expression match indices via the/d flag, which provides start and end indices for matched substrings; thecause property onError objects, which can be used to record a causation chain in errors; theat method for Strings, Arrays, andObject.hasOwn, a convenient alternative toObject.prototype.hasOwnProperty.
ECMAScript 2023, the 14th edition, introduced thetoSorted,toReversed,with,findLast, andfindLastIndex methods onArray.prototype andTypedArray.prototype, as well as thetoSpliced method onArray.prototype; added support for#! comments at the beginning of files to better facilitate executable ECMAScript files; and allowed the use of most Symbols as keys in weak collections.
ECMAScript 2024, the 15th edition, added facilities for resizing and transferring ArrayBuffers and SharedArrayBuffers; added a new RegExp/v flag for creating RegExps with more advanced features for working with sets of strings; and introduced thePromise.withResolvers convenience method for constructing Promises, theObject.groupBy andMap.groupBy methods for aggregating data, theAtomics.waitAsync method for asynchronously waiting for a change to shared memory, and theString.prototype.isWellFormed andString.prototype.toWellFormed methods for checking and ensuring that strings contain only well-formed Unicode.
Dozens of individuals representing many organizations have made very significant contributions within Ecma TC39 to the development of this edition and to the prior editions. In addition, a vibrant community has emerged supporting TC39's ECMAScript efforts. This community has reviewed numerous drafts, filed thousands of bug reports, performed implementation experiments, contributed test suites, and educated the world-wide developer community about ECMAScript. Unfortunately, it is impossible to identify and acknowledge every person and organization who has contributed to this effort.
Allen Wirfs-Brock
ECMA-262, Project Editor, 6th Edition
Brian Terlson
ECMA-262, Project Editor, 7th through 10th Editions
Jordan Harband
ECMA-262, Project Editor, 10th through 12th Editions
Shu-yu Guo
ECMA-262, Project Editor, 12th through 15th Editions
Michael Ficarra
ECMA-262, Project Editor, 12th through 15th Editions
Kevin Gibbons
ECMA-262, Project Editor, 12th through 15th Editions
1 Scope
This Standard defines the ECMAScript 2024 general-purpose programming language.
2 Conformance
A conforming implementation of ECMAScript must provide and support all the types, values, objects, properties, functions, and program syntax and semantics described in this specification.
A conforming implementation of ECMAScript must interpret source text input in conformance with the latest version of the Unicode Standard and ISO/IEC 10646.
A conforming implementation of ECMAScript that provides an application programming interface (API) that supports programs that need to adapt to the linguistic and cultural conventions used by different human languages and countries must implement the interface defined by the most recent edition of ECMA-402 that is compatible with this specification.
A conforming implementation of ECMAScript may provide additional types, values, objects, properties, and functions beyond those described in this specification. In particular, a conforming implementation of ECMAScript may provide properties not described in this specification, and values for those properties, for objects that are described in this specification.
A conforming implementation of ECMAScript may support program and regular expression syntax not described in this specification. In particular, a conforming implementation of ECMAScript may support program syntax that makes use of any “future
A conforming implementation of ECMAScript must not implement any extension that is listed as a Forbidden Extension in subclause
A conforming implementation of ECMAScript must not redefine any facilities that are not
A conforming implementation of ECMAScript may choose to implement or not implementNormative Optional subclauses. If any Normative Optional behaviour is implemented, all of the behaviour in the containing Normative Optional clause must be implemented. A Normative Optional clause is denoted in this specification with the words "Normative Optional" in a coloured box, as shown below.
2.1 Example Normative Optional Clause Heading
Example clause contents.
A conforming implementation of ECMAScript must implementLegacy subclauses, unless they are also marked as Normative Optional. All of the language features and behaviours specified within Legacy subclauses have one or more undesirable characteristics. However, their continued usage in existing applications prevents their removal from this specification. These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code.
2.2 Example Legacy Clause Heading
Example clause contents.
2.3 Example Legacy Normative Optional Clause Heading
Example clause contents.
3 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
The Unicode Standard.
https://unicode.org/versions/latest
ISO/IEC 10646,Information Technology — Universal Multiple-Octet Coded Character Set (UCS) plus Amendment 1:2005, Amendment 2:2006, Amendment 3:2008, Amendment 4:2008, and additional amendments and corrigenda, or successor.
ECMA-402,ECMAScript Internationalization API Specification, specifically the annual edition corresponding to this edition of this specification.
https://www.ecma-international.org/publications-and-standards/standards/ecma-402/
ECMA-404,The JSON Data Interchange Format.
https://www.ecma-international.org/publications-and-standards/standards/ecma-404/
4 Overview
This section contains a non-normative overview of the ECMAScript language.
ECMAScript is an object-oriented programming language for performing computations and manipulating computational objects within a
ECMAScript was originally designed to be used as a scripting language, but has become widely used as a general-purpose programming language. Ascripting language is a programming language that is used to manipulate, customize, and automate the facilities of an existing system. In such systems, useful functionality is already available through a user interface, and the scripting language is a mechanism for exposing that functionality to program control. In this way, the existing system is said to provide a
ECMAScript was originally designed to be aWeb scripting language, providing a mechanism to enliven Web pages in browsers and to perform server computation as part of a Web-based client-server architecture. ECMAScript is now used to provide core scripting capabilities for a variety of
ECMAScript usage has moved beyond simple scripting and it is now used for the full spectrum of programming tasks in many different environments and scales. As the usage of ECMAScript has expanded, so have the features and facilities it provides. ECMAScript is now a fully featured general-purpose programming language.
4.1 Web Scripting
A web browser provides an ECMAScript
A web server provides a different
Each Web browser and server that supports ECMAScript supplies its own
4.2 Hosts and Implementations
To aid integrating ECMAScript into
Animplementation is an external source that further defines facilities enumerated in Annex
Animplementation-defined facility is one that defers its definition to an external source without further qualification. This specification does not make any recommendations for particular behaviours, and conforming implementations are free to choose any behaviour within the constraints put forth by this specification.
Animplementation-approximated facility is one that defers its definition to an external source while recommending an ideal behaviour. While conforming implementations are free to choose any behaviour within the constraints put forth by this specification, they are encouraged to strive to approximate the ideal. Some mathematical operations, such asMath.exp
Ahost is an external source that further defines facilities listed in Annex
Ahost hook is an abstract operation that is defined in whole or in part by an external source. All
- It must return either a
normal completion or athrow completion .
Ahost-defined facility is one that defers its definition to an external source without further qualification and is listed in Annex
Ahost environment is a particular choice of definition for all
This specification follows the editorial convention of always using the most specific term. For example, if a facility is
Both
4.3 ECMAScript Overview
The following is an informal overview of ECMAScript—not all parts of the language are described. This overview is not part of the standard proper.
ECMAScript is object-based: basic language and
ECMAScript defines a collection ofbuilt-in objects that round out the definition of ECMAScript entities. These built-in objects include theObject,Function,Boolean,Symbol, and variousError objects; objects that represent and manipulate numeric values includingMath,Number, andDate; the text processing objectsString andRegExp; objects that are indexed collections of values includingArray and nine different kinds of Typed Arrays whose elements all have a specific numeric data representation; keyed collections includingMap andSet objects; objects supporting structured data including theJSON object,ArrayBuffer,SharedArrayBuffer, andDataView; objects supporting control abstractions including generator functions andPromise objects; and reflection objects includingProxy andReflect.
ECMAScript also defines a set of built-inoperators. ECMAScript operators include various unary operations, multiplicative operators, additive operators, bitwise shift operators, relational operators, equality operators, binary bitwise operators, binary logical operators, assignment operators, and the comma operator.
Large ECMAScript programs are supported bymodules which allow a program to be divided into multiple sequences of statements and declarations. Each module explicitly identifies declarations it uses that need to be provided by other modules and which of its declarations are available for use by other modules.
ECMAScript syntax intentionally resembles Java syntax. ECMAScript syntax is relaxed to enable it to serve as an easy-to-use scripting language. For example, a variable is not required to have its type declared nor are types associated with properties, and defined functions are not required to have their declarations appear textually before calls to them.
4.3.1 Objects
Even though ECMAScript includes syntax for class definitions, ECMAScript objects are not fundamentally class-based such as those in C++, Smalltalk, or Java. Instead objects may be created in various ways including via a literal notation or vianew Date(2009, 11) creates a new Date object. Invoking aDate() produces a string representation of the current date and time rather than an object.
Every object created by a
In a class-based object-oriented language, in general, state is carried by instances, methods are carried by classes, and inheritance is only of structure and behaviour. In ECMAScript, the state and methods are carried by objects, while structure, behaviour, and state are all inherited.
All objects that do not directly contain a particular property that their prototype contains share that property and its value. Figure 1 illustrates this:
CF is anew expressions:cf1,cf2,cf3,cf4, andcf5. Each of these objects contains properties named
Unlike most class-based object languages, properties can be added to objects dynamically by assigning values to them. That is,
Although ECMAScript objects are not inherently class-based, it is often convenient to define class-like abstractions based upon a common pattern of
4.3.2 The Strict Variant of ECMAScript
The ECMAScript Language recognizes the possibility that some users of the language may wish to restrict their usage of some features available in the language. They might do so in the interests of security, to avoid what they consider to be error-prone features, to get enhanced error checking, or for other reasons of their choosing. In support of this possibility, ECMAScript defines a strict variant of the language. The strict variant of the language excludes some specific syntactic and semantic features of the regular ECMAScript language and modifies the detailed semantics of some features. The strict variant also specifies additional error conditions that must be reported by throwing error exceptions in situations that are not specified as errors by the non-strict form of the language.
The strict variant of ECMAScript is commonly referred to as thestrict mode of the language. Strict mode selection and use of the strict mode syntax and semantics of ECMAScript is explicitly made at the level of individual
In order to conform to this specification, an ECMAScript implementation must implement both the full unrestricted ECMAScript language and the strict variant of the ECMAScript language as defined by this specification. In addition, an implementation must support the combination of unrestricted and strict mode source text units into a single composite program.
4.4 Terms and Definitions
For the purposes of this document, the following terms and definitions apply.
4.4.1 implementation-approximated
an
4.4.2 implementation-defined
an
4.4.3 host-defined
same as
Editorially, see clause
4.4.4 type
set of data values as defined in clause
4.4.5 primitive value
member of one of the types Undefined, Null, Boolean, Number, BigInt, Symbol, or String as defined in clause
A primitive value is a datum that is represented directly at the lowest level of the language implementation.
4.4.6 object
member of the type Object
An object is a collection of properties and has a single prototype object. The prototype may be
4.4.7 constructor
The value of a
4.4.8 prototype
object that provides shared properties for other objects
When aconstructor.prototype, and properties added to an object's prototype are shared, through inheritance, by all objects sharing the prototype. Alternatively, a new object may be created with an explicitly specified prototype by using theObject.create built-in function.
4.4.9 ordinary object
object that has the default behaviour for the essential internal methods that must be supported by all objects
4.4.10 exotic object
object that does not have the default behaviour for one or more of the essential internal methods
Any object that is not an
4.4.11 standard object
object whose semantics are defined by this specification
4.4.12 built-in object
object specified and supplied by an ECMAScript implementation
Standard built-in objects are defined in this specification. An ECMAScript implementation may specify and supply additional kinds of built-in objects.
4.4.13 undefined value
primitive value used when a variable has not been assigned a value
4.4.14 Undefined type
type whose sole value is the
4.4.15 null value
primitive value that represents the intentional absence of any object value
4.4.16 Null type
type whose sole value is the
4.4.17 Boolean value
member of the
There are only two Boolean values,
4.4.18 Boolean type
type consisting of the primitive values
4.4.19 Boolean object
member of the
A Boolean object is created by using the Booleannew expression, supplying a Boolean value as an argument. The resulting object has an internal slot whose value is the Boolean value. A Boolean object can be coerced to a Boolean value.
4.4.20 String value
primitive value that is a
A String value is a member of the
4.4.21 String type
set of all possible String values
4.4.22 String object
member of the
A String object is created by using the Stringnew expression, supplying a String value as an argument. The resulting object has an internal slot whose value is the String value. A String object can be coerced to a String value by calling the String
4.4.23 Number value
primitive value corresponding to a double-precision 64-bit binary format
A Number value is a member of the
4.4.24 Number type
set of all possible Number values including the special “Not-a-Number” (NaN) value, positive infinity, and negative infinity
4.4.25 Number object
member of the
A Number object is created by using the Numbernew expression, supplying a Number value as an argument. The resulting object has an internal slot whose value is the Number value. A Number object can be coerced to a Number value by calling the Number
4.4.26 Infinity
Number value that is the positive infinite Number value
4.4.27 NaN
Number value that is an
4.4.28 BigInt value
primitive value corresponding to an arbitrary-precision
4.4.29 BigInt type
set of all possible BigInt values
4.4.30 BigInt object
member of the
4.4.31 Symbol value
primitive value that represents a unique, non-String Object
4.4.32 Symbol type
set of all possible Symbol values
4.4.33 Symbol object
member of the
4.4.34 function
member of the
In addition to its properties, a function contains executable code and state that determine how it behaves when invoked. A function's code may or may not be written in ECMAScript.
4.4.35 built-in function
built-in object that is a function
Examples of built-in functions includeparseInt andMath.exp. A
4.4.36 built-in constructor
built-in function that is a
Examples of built-inObject andFunction. A
4.4.37 property
part of an object that associates a key (either a String value or a Symbol value) and a value
Depending upon the form of the property the value may be represented either directly as a data value (a primitive value, an object, or a
4.4.38 method
function that is the value of a property
When a function is called as a method of an object, the object is passed to the function as its
4.4.39 built-in method
method that is a built-in function
Standard built-in methods are defined in this specification. A
4.4.40 attribute
internal value that defines some characteristic of a property
4.4.41 own property
property that is directly contained by its object
4.4.42 inherited property
property of an object that is not an own property but is a property (either own or inherited) of the object's prototype
4.5 Organization of This Specification
The remainder of this specification is organized as follows:
Clause
Clauses
Clauses
Clauses
Clause
5 Notational Conventions
5.1 Syntactic and Lexical Grammars
5.1.1 Context-Free Grammars
Acontext-free grammar consists of a number ofproductions. Each production has an abstract symbol called anonterminal as itsleft-hand side, and a sequence of zero or more nonterminal andterminal symbols as itsright-hand side. For each grammar, the terminal symbols are drawn from a specified alphabet.
Achain production is a production that has exactly one nonterminal symbol on its right-hand side along with zero or more terminal symbols.
Starting from a sentence consisting of a single distinguished nonterminal, called thegoal symbol, a given context-free grammar specifies alanguage, namely, the (perhaps infinite) set of possible sequences of terminal symbols that can result from repeatedly replacing any nonterminal in the sequence with a right-hand side of a production for which the nonterminal is the left-hand side.
5.1.2 The Lexical and RegExp Grammars
Alexical grammar for ECMAScript is given in clause
Input elements other than white space and comments form the terminal symbols for the syntactic grammar for ECMAScript and are called ECMAScripttokens. These tokens are the/*…*/ regardless of whether it spans more than one line) is likewise simply discarded if it contains no line terminator; but if a
ARegExp grammar for ECMAScript is given in
Productions of the lexical and RegExp grammars are distinguished by having two colons “::” as separating punctuation. The lexical and RegExp grammars share some productions.
5.1.3 The Numeric String Grammar
Anumeric string grammar appears in
Productions of the numeric string grammar are distinguished by having three colons “:::” as punctuation, and are never used for parsing source text.
5.1.4 The Syntactic Grammar
Thesyntactic grammar for ECMAScript is given in clauses
When a stream of code points is to be parsed as an ECMAScript
When a parse is successful, it constructs aparse tree, a rooted tree structure in which each node is aParse Node. Each Parse Node is aninstance of a symbol in the grammar; it represents a span of the source text that can be derived from that symbol. The root node of the parse tree, representing the whole of the source text, is an instance of the parse's
New Parse Nodes are instantiated for each invocation of the parser and never reused between parses even of identical source text. Parse Nodes are consideredthe same Parse Node if and only if they represent the same span of source text, are instances of the same grammar symbol, and resulted from the same parser invocation.
Parsing the same String multiple times will lead to different Parse Nodes. For example, consider:
let str ="1 + 1;";eval(str);eval(str);Each call toeval converts the value ofstr into
Productions of the syntactic grammar are distinguished by having just one colon “:” as punctuation.
The syntactic grammar as presented in clauses
In certain cases, in order to avoid ambiguities, the syntactic grammar uses generalized productions that permit token sequences that do not form a valid ECMAScript
- The sequence of tokens originally matched byP is parsed again usingN as the
goal symbol . IfN takes grammatical parameters, then they are set to the same values used whenP was originally parsed. - If the sequence of tokens can be parsed as a single instance ofN, with no tokens left over, then:
- We refer to that instance ofN (a Parse Node, unique for a givenP) as "theN that iscovered byP".
- All Early Error rules forN and its derived productions also apply to theN that is covered byP.
- Otherwise (if the parse fails), it is an early Syntax Error.
5.1.5 Grammar Notation
5.1.5.1 Terminal Symbols
In the ECMAScript grammars, some terminal symbols are shown infixed-width font. These are to appear in a source text exactly as written. All terminal symbol code points specified in this way are to be understood as the appropriate Unicode code points from the Basic Latin block, as opposed to any similar-looking code points from other Unicode ranges. A code point in a terminal symbol cannot be expressed by a\
In grammars whose terminal symbols are individual Unicode code points (i.e., the lexical, RegExp, and numeric string grammars), a contiguous run of multiple fixed-width code points appearing in a production is a simple shorthand for the same sequence of code points, written as standalone terminal symbols.
For example, the production:
is a shorthand for:
In contrast, in the syntactic grammar, a contiguous run of fixed-width code points is a single terminal symbol.
Terminal symbols come in two other forms:
- In the lexical and RegExp grammars, Unicode code points without a conventional printed representation are instead shown in the form "<ABBREV>" where "ABBREV" is a mnemonic for the code point or set of code points. These forms are defined in
Unicode Format-Control Characters ,White Space , andLine Terminators . - In the syntactic grammar, certain terminal symbols (e.g.
IdentifierName andRegularExpressionLiteral ) are shown in italics, as they refer to the nonterminals of the same name in the lexical grammar.
5.1.5.2 Nonterminal Symbols and Productions
Nonterminal symbols are shown initalic type. The definition of a nonterminal (also called a “production”) is introduced by the name of the nonterminal being defined followed by one or more colons. (The number of colons indicates to which grammar the production belongs.) One or more alternative right-hand sides for the nonterminal then follow on succeeding lines. For example, the syntactic definition:
states that the nonterminalwhile, followed by a left parenthesis token, followed by an
states that an
5.1.5.3 Optional Symbols
The subscripted suffix “opt”, which may appear after a terminal or nonterminal, indicates an optional symbol. The alternative containing the optional symbol actually specifies two right-hand sides, one that omits the optional element and one that includes it. This means that:
is a convenient abbreviation for:
and that:
is a convenient abbreviation for:
which in turn is an abbreviation for:
so, in this example, the nonterminal
5.1.5.4 Grammatical Parameters
A production may be parameterized by a subscripted annotation of the form “[parameters]”, which may appear as a suffix to the nonterminal symbol defined by the production. “parameters” may be either a single name or a comma separated list of names. A parameterized production is shorthand for a set of productions defining all combinations of the parameter names, preceded by an underscore, appended to the parameterized nonterminal symbol. This means that:
is a convenient abbreviation for:
and that:
is an abbreviation for:
Multiple parameters produce a combinatory number of productions, not all of which are necessarily referenced in a complete grammar.
References to nonterminals on the right-hand side of a production can also be parameterized. For example:
is equivalent to saying:
and:
is equivalent to:
A nonterminal reference may have both a parameter list and an “opt” suffix. For example:
is an abbreviation for:
Prefixing a parameter name with “?” on a right-hand side nonterminal reference makes that parameter value dependent upon the occurrence of the parameter name on the reference to the current production's left-hand side symbol. For example:
is an abbreviation for:
If a right-hand side alternative is prefixed with “[+parameter]” that alternative is only available if the named parameter was used in referencing the production's nonterminal symbol. If a right-hand side alternative is prefixed with “[~parameter]” that alternative is only available if the named parameter wasnot used in referencing the production's nonterminal symbol. This means that:
is an abbreviation for:
and that:
is an abbreviation for:
5.1.5.5 one of
When the words “one of” follow the colon(s) in a grammar definition, they signify that each of the terminal symbols on the following line or lines is an alternative definition. For example, the lexical grammar for ECMAScript contains the production:
which is merely a convenient abbreviation for:
5.1.5.6 [empty]
If the phrase “[empty]” appears as the right-hand side of a production, it indicates that the production's right-hand side contains no terminals or nonterminals.
5.1.5.7 Lookahead Restrictions
If the phrase “[lookahead =seq]” appears in the right-hand side of a production, it indicates that the production may only be used if the token sequenceseq is a prefix of the immediately following input token sequence. Similarly, “[lookahead ∈set]”, whereset is a
These conditions may be negated. “[lookahead ≠seq]” indicates that the containing production may only be used ifseq isnot a prefix of the immediately following input token sequence, and “[lookahead ∉set]” indicates that the production may only be used ifno element ofset is a prefix of the immediately following token sequence.
As an example, given the definitions:
the definition:
matches either the lettern followed by one or more decimal digits the first of which is even, or a decimal digit not followed by another decimal digit.
Note that when these phrases are used in the syntactic grammar, it may not be possible to unambiguously identify the immediately following token sequence because determining later tokens requires knowing which lexical
5.1.5.8 [noLineTerminator here]
If the phrase “[no
indicates that the production may not be used if athrow token and the
Unless the presence of a
5.1.5.9 but not
The right-hand side of a production may specify that certain expansions are not permitted by using the phrase “but not” and then indicating the expansions to be excluded. For example, the production:
means that the nonterminal
5.1.5.10 Descriptive Phrases
Finally, a few nonterminal symbols are described by a descriptive phrase in sans-serif type in cases where it would be impractical to list all the alternatives:
5.2 Algorithm Conventions
The specification often uses a numbered list to specify steps in an algorithm. These algorithms are used to precisely specify the required semantics of ECMAScript language constructs. The algorithms are not intended to imply the use of any specific implementation technique. In practice, there may be more efficient algorithms available to implement a given feature.
Algorithms may be explicitly parameterized with an ordered, comma-separated sequence of alias names which may be used within the algorithm steps to reference the argument passed in that position. Optional parameters are denoted with surrounding brackets ([ ,name ]) and are no different from required parameters within algorithm steps. A rest parameter may appear at the end of a parameter list, denoted with leading ellipsis (, ...name). The rest parameter captures all of the arguments provided following the required and optional parameters into a
Algorithm steps may be subdivided into sequential substeps. Substeps are indented and may themselves be further divided into indented substeps. Outline numbering conventions are used to identify substeps with the first level of substeps labelled with lowercase alphabetic characters and the second level of substeps labelled with lowercase roman numerals. If more than three levels are required these rules repeat with the fourth level using numeric labels. For example:
- Top-level step
- Substep.
- Substep.
- Subsubstep.
- Subsubsubstep
- Subsubsubsubstep
- Subsubsubsubsubstep
- Subsubsubsubstep
- Subsubsubstep
- Subsubstep.
A step or substep may be written as an “if” predicate that conditions its substeps. In this case, the substeps are only applied if the predicate is true. If a step or substep begins with the word “else”, it is a predicate that is the negation of the preceding “if” predicate step at the same level.
A step may specify the iterative application of its substeps.
A step that begins with “Assert:” asserts an invariant condition of its algorithm. Such assertions are used to make explicit algorithmic invariants that would otherwise be implicit. Such assertions add no additional semantic requirements and hence need not be checked by an implementation. They are used simply to clarify algorithms.
Algorithm steps may declare named aliases for any value using the form “Letx besomeValue”. These aliases are reference-like in that bothx andsomeValue refer to the same underlying data and modifications to either are visible to both. Algorithm steps that want to avoid this reference-like behaviour should explicitly make a copy of the right-hand side: “Letx be a copy ofsomeValue” creates a shallow copy ofsomeValue.
Once declared, an alias may be referenced in any subsequent steps and must not be referenced from steps prior to the alias's declaration. Aliases may be modified using the form “Setx tosomeOtherValue”.
5.2.1 Abstract Operations
In order to facilitate their use in multiple parts of this specification, some algorithms, calledabstract operations, are named and written in parameterized functional form so that they may be referenced by name from within other algorithms. Abstract operations are typically referenced using a functional application style such as OperationName(arg1,arg2). Some abstract operations are treated as polymorphically dispatched methods of class-like specification abstractions. Such method-like abstract operations are typically referenced using a method application style such assomeValue.OperationName(arg1,arg2).
5.2.2 Syntax-Directed Operations
Asyntax-directed operation is a named operation whose definition consists of algorithms, each of which is associated with one or more productions from one of the ECMAScript grammars. A production that has multiple alternative definitions will typically have a distinct algorithm for each alternative. When an algorithm is associated with a grammar production, it may reference the terminal and nonterminal symbols of the production alternative as if they were parameters of the algorithm. When used in this manner, nonterminal symbols refer to the actual alternative definition that is matched when parsing the source text. Thesource text matched by a grammar production or
When an algorithm is associated with a production alternative, the alternative is typically shown without any “[ ]” grammar annotations. Such annotations should only affect the syntactic recognition of the alternative and have no effect on the associated semantics for the alternative.
Syntax-directed operations are invoked with a parse node and, optionally, other parameters by using the conventions on steps
- Letstatus be SyntaxDirectedOperation of
SomeNonTerminal . - LetsomeParseNode be the parse of some source text.
- Perform SyntaxDirectedOperation ofsomeParseNode.
- Perform SyntaxDirectedOperation ofsomeParseNode with argument
"value" .
Unless explicitly specified otherwise, all
but the
Runtime Semantics:
- Return
Evaluation ofStatementList .
5.2.3 Runtime Semantics
Algorithms which specify semantics that must be called at runtime are calledruntime semantics. Runtime semantics are defined by
5.2.3.1 Completion (completionRecord )
The abstract operation Completion takes argumentcompletionRecord (a
Assert :completionRecord is aCompletion Record .- ReturncompletionRecord.
5.2.3.2 Throw an Exception
Algorithms steps that say to throw an exception, such as
- Throw a
TypeError exception.
mean the same things as:
- Return
ThrowCompletion (a newly createdTypeError object).
5.2.3.3 ReturnIfAbrupt
Algorithms steps that say or are otherwise equivalent to:
ReturnIfAbrupt (argument).
mean the same thing as:
Assert :argument is aCompletion Record .- Ifargument is an
abrupt completion , returnCompletion (argument). - Else, setargument toargument.[[Value]].
Algorithms steps that say or are otherwise equivalent to:
ReturnIfAbrupt (AbstractOperation()).
mean the same thing as:
- LethygienicTemp be AbstractOperation().
Assert :hygienicTemp is aCompletion Record .- IfhygienicTemp is an
abrupt completion , returnCompletion (hygienicTemp). - Else, sethygienicTemp tohygienicTemp.[[Value]].
WherehygienicTemp is ephemeral and visible only in the steps pertaining to ReturnIfAbrupt.
Algorithms steps that say or are otherwise equivalent to:
- Letresult be AbstractOperation(
ReturnIfAbrupt (argument)).
mean the same thing as:
Assert :argument is aCompletion Record .- Ifargument is an
abrupt completion , returnCompletion (argument). - Else, setargument toargument.[[Value]].
- Letresult be AbstractOperation(argument).
5.2.3.4 ReturnIfAbrupt Shorthands
Invocations of? indicate that
- ? OperationName().
is equivalent to the following step:
ReturnIfAbrupt (OperationName()).
Similarly, for method application style, the step:
- ? someValue.OperationName().
is equivalent to:
ReturnIfAbrupt (someValue.OperationName()).
Similarly, prefix! is used to indicate that the following invocation of an abstract or
- Letval be ! OperationName().
is equivalent to the following steps:
- Letval be OperationName().
Assert :val is anormal completion .- Setval toval.[[Value]].
! or? before the invocation of the operation:
- Perform ! SyntaxDirectedOperation of
NonTerminal .
5.2.3.5 Implicit Normal Completion
In algorithms within
- when the result of applying
Completion ,NormalCompletion , orThrowCompletion is directly returned - when the result of constructing a
Completion Record is directly returned
It is an editorial error if a
- Return
true .
means the same things as any of
- Return
NormalCompletion (true ).
or
- Letcompletion be
NormalCompletion (true ). - Return
Completion (completion).
or
- Return
Completion Record {[[Type]]:normal ,[[Value]]:true ,[[Target]]:empty }.
Note that, through the
- Return ? completion.
The following example would be an editorial error because a
- Letcompletion be
NormalCompletion (true ). - Returncompletion.
5.2.4 Static Semantics
Context-free grammars are not sufficiently powerful to express all the rules that define whether a stream of input elements form a valid ECMAScript
Static Semantic Rules have names and typically are defined using an algorithm. Named Static Semantic Rules are associated with grammar productions and a production that has multiple alternative definitions will typically have for each alternative a distinct algorithm for each applicable named static semantic rule.
A special kind of static semantic rule is anEarly Error Rule.
5.2.5 Mathematical Operations
This specification makes reference to these kinds of numeric values:
- Mathematical values: Arbitrary real numbers, used as the default numeric type.
- Extended mathematical values:
Mathematical values together with +∞ and -∞. - Numbers:
IEEE 754-2019 double-precision floating point values. - BigInts:
ECMAScript language values representing arbitraryintegers in a one-to-one correspondence.
In the language of this specification, numerical values are distinguished among different numeric kinds using subscript suffixes. The subscript𝔽 refers to Numbers, and the subscriptℤ refers to BigInts. Numeric values without a subscript suffix refer to
Numeric operators such as +, ×, =, and ≥ refer to those operations as determined by the type of the operands. When applied to
In general, when this specification refers to a numerical value, such as in the phrase, "the length ofy" or "the
Numeric operators applied to mixed-type operands (such as a Number and a
This specification denotes most numeric values in base 10; it also uses numeric values of the form 0x followed by digits 0-9 or A-F as base-16 values.
When the terminteger is used in this specification, it refers to a
Conversions between
The mathematical function
The mathematical function
The notation “
The phrase "the result ofclampingx betweenlower andupper" (wherex is an
The mathematical function
The mathematical function
Mathematical functions
Aninterval from lower bounda to upper boundb is a possibly-infinite, possibly-empty set of numeric values of the same numeric type. Each bound will be described as either inclusive or exclusive, but not both. There are four kinds of intervals, as follows:
- An
interval froma (inclusive) tob (inclusive), also called aninclusive interval froma tob, includes all valuesx of the same numeric type such thata ≤x ≤b, and no others. - An
interval froma (inclusive) tob (exclusive) includes all valuesx of the same numeric type such thata ≤x <b, and no others. - An
interval froma (exclusive) tob (inclusive) includes all valuesx of the same numeric type such thata <x ≤b, and no others. - An
interval froma (exclusive) tob (exclusive) includes all valuesx of the same numeric type such thata <x <b, and no others.
For example, the
5.2.6 Value Notation
In this specification,Function.prototype.apply orlet n = 42;.
5.2.7 Identity
In this specification, both specification values and
From the perspective of this specification, the word “is” is used to compare two values for equality, as in “Ifbool is
From the perspective of the ECMAScript language, language values are compared for equality using the
For specification values, examples of values without specification identity include, but are not limited to:
Specification identity agrees with language identity for all
6 ECMAScript Data Types and Values
Algorithms within this specification manipulate values each of which has an associated type. The possible value types are exactly those defined in this clause. Types are further subclassified into
Within this specification, the notation “Type(x)” is used as shorthand for “thetype ofx” where “type” refers to the ECMAScript language and specification types defined in this clause.
6.1 ECMAScript Language Types
AnECMAScript language type corresponds to values that are directly manipulated by an ECMAScript programmer using the ECMAScript language. The ECMAScript language types are Undefined, Null, Boolean, String, Symbol, Number, BigInt, and Object. AnECMAScript language value is a value that is characterized by an ECMAScript language type.
6.1.1 The Undefined Type
The Undefined type has exactly one value, called
6.1.2 The Null Type
The Null type has exactly one value, called
6.1.3 The Boolean Type
TheBoolean type represents a logical entity having two values, called
6.1.4 The String Type
TheString type is the set of all ordered sequences of zero or more 16-bit unsigned
ECMAScript operations that do not interpret String contents apply no further semantics. Operations that do interpret String values treat each element as a single UTF-16 code unit. However, ECMAScript does not restrict the value of or relationships between these code units, so operations that further interpret String contents as sequences of Unicode code points encoded in UTF-16 must account for ill-formed subsequences. Such operations apply special treatment to every code unit with a numeric value in the
- A code unit that is not a
leading surrogate and not atrailing surrogate is interpreted as a code point with the same value. - A sequence of two code units, where the first code unitc1 is a
leading surrogate and the second code unitc2 atrailing surrogate , is asurrogate pair and is interpreted as a code point with the value (c1 - 0xD800) × 0x400 + (c2 - 0xDC00) + 0x10000. (See11.1.3 ) - A code unit that is a
leading surrogate ortrailing surrogate , but is not part of asurrogate pair , is interpreted as a code point with the same value.
The functionString.prototype.normalize (seeString.prototype.localeCompare (see
The rationale behind this design was to keep the implementation of Strings as simple and high-performing as possible. If
In this specification, the phrase "thestring-concatenation ofA,B, ..." (where each argument is a String value, a code unit, or a sequence of code units) denotes the String value whose sequence of code units is the concatenation of the code units (in order) of each of the arguments (in order).
The phrase "thesubstring ofS frominclusiveStart toexclusiveEnd" (whereS is a String value or a sequence of code units andinclusiveStart andexclusiveEnd are
The phrase "the ASCII word characters" denotes the following String value, which consists solely of every letter and number in the Unicode Basic Latin block along with U+005F (LOW LINE):
For historical reasons, it has significance to various algorithms.
6.1.4.1 StringIndexOf (string,searchValue,fromIndex )
The abstract operation StringIndexOf takes argumentsstring (a String),searchValue (a String), andfromIndex (a non-negative
- Letlen be the length ofstring.
- IfsearchValue is the empty String andfromIndex ≤len, returnfromIndex.
- LetsearchLen be the length ofsearchValue.
- For each
integer i such thatfromIndex ≤i ≤len -searchLen, in ascending order, do- Letcandidate be the
substring ofstring fromi toi +searchLen. - Ifcandidate issearchValue, returni.
- Letcandidate be the
- Return -1.
IfsearchValue is the empty String andfromIndex ≤ the length ofstring, this algorithm returnsfromIndex. The empty String is effectively found at every position within a string, including after the last code unit.
This algorithm always returns -1 iffromIndex + the length ofsearchValue > the length ofstring.
6.1.5 The Symbol Type
TheSymbol type is the set of all non-String values that may be used as the key of an Object property (
Each possible Symbol value is unique and immutable.
Each Symbol value immutably holds an associated value called[[Description]] that is either
6.1.5.1 Well-Known Symbols
Well-known symbols are built-in Symbol values that are explicitly referenced by algorithms of this specification. They are typically used as the keys of properties whose values serve as extension points of a specification algorithm. Unless otherwise specified, well-known symbols values are shared by all
Within this specification a well-known symbol is referred to by using a notation of the form @@name, where “name” is one of the values listed in
| Specification Name | [[Description]] | Value and Purpose |
|---|---|---|
| @@asyncIterator | A method that returns the default AsyncIterator for an object. Called by the semantics of thefor-await-of statement. | |
| @@hasInstance | A method that determines if ainstanceof operator. | |
| @@isConcatSpreadable | A Boolean valued property that if true indicates that an object should be flattened to its array elements byArray.prototype.concat | |
| @@iterator | A method that returns the default Iterator for an object. Called by the semantics of the for-of statement. | |
| @@match | A regular expression method that matches the regular expression against a string. Called by theString.prototype.match | |
| @@matchAll | A regular expression method that returns an iterator, that yields matches of the regular expression against a string. Called by theString.prototype.matchAll | |
| @@replace | A regular expression method that replaces matched substrings of a string. Called by theString.prototype.replace | |
| @@search | A regular expression method that returns the index within a string that matches the regular expression. Called by theString.prototype.search | |
| @@species | A function valued property that is the | |
| @@split | A regular expression method that splits a string at the indices that match the regular expression. Called by theString.prototype.split | |
| @@toPrimitive | A method that converts an object to a corresponding primitive value. Called by the | |
| @@toStringTag | A String valued property that is used in the creation of the default string description of an object. Accessed by the built-in methodObject.prototype.toString | |
| @@unscopables | An object valued property whose own and inherited property names are property names that are excluded from thewith environment bindings of the associated object. |
6.1.6 Numeric Types
ECMAScript has two built-in numeric types: Number and BigInt. The following
Because the numeric types are in general not convertible without loss of precision or truncation, the ECMAScript language provides no implicit conversion among these types. Programmers must explicitly callNumber andBigInt functions to convert among types when calling a function which requires another type.
The first and subsequent editions of ECMAScript have provided, for certain operators, implicit numeric conversions that could lose precision or
6.1.6.1 The Number Type
TheNumber type has exactly 18,437,736,874,454,810,627 (that is,NaN.) In some implementations, external code might be able to detect a difference between various Not-a-Number values, but such behaviour is
There are two other special values, called+Infinity (or simplyInfinity) and-Infinity.)
The other 18,437,736,874,454,810,624 (that is,
Note that there is both a+0 (or simply0) and-0.)
The 18,437,736,874,454,810,622 (that is,
18,428,729,675,200,069,632 (that is,
wheres is 1 or -1,m is an
The remaining 9,007,199,254,740,990 (that is,
wheres is 1 or -1,m is an
Note that all the positive and negative
A
In this specification, the phrase “theNumber value forx” wherex represents an exact real mathematical quantity (which might even be an irrational number such as π) means a Number value chosen in the following manner. Consider the set of all
The
Some ECMAScript operators deal only with
6.1.6.1.1 Number::unaryMinus (x )
The abstract operation Number::unaryMinus takes argumentx (a Number) and returns a Number. It performs the following steps when called:
- Ifx is
NaN , returnNaN . - Return the result of negatingx; that is, compute a Number with the same magnitude but opposite sign.
6.1.6.1.2 Number::bitwiseNOT (x )
The abstract operation Number::bitwiseNOT takes argumentx (a Number) and returns an
- LetoldValue be !
ToInt32 (x). - Return the result of applying bitwise complement tooldValue. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.3 Number::exponentiate (base,exponent )
The abstract operation Number::exponentiate takes argumentsbase (a Number) andexponent (a Number) and returns a Number. It returns an
- Ifexponent is
NaN , returnNaN . - Ifexponent is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Ifbase is
NaN , returnNaN . - Ifbase is
+∞ 𝔽, then- Ifexponent >
+0 𝔽, return+∞ 𝔽. Otherwise, return+0 𝔽.
- Ifexponent >
- Ifbase is
-∞ 𝔽, then- Ifexponent >
+0 𝔽, then- Ifexponent is an odd
integral Number , return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- Ifexponent is an odd
- Else,
- Ifexponent is an odd
integral Number , return-0 𝔽. Otherwise, return+0 𝔽.
- Ifexponent is an odd
- Ifexponent >
- Ifbase is
+0 𝔽, then- Ifexponent >
+0 𝔽, return+0 𝔽. Otherwise, return+∞ 𝔽.
- Ifexponent >
- Ifbase is
-0 𝔽, then- Ifexponent >
+0 𝔽, then- Ifexponent is an odd
integral Number , return-0 𝔽. Otherwise, return+0 𝔽.
- Ifexponent is an odd
- Else,
- Ifexponent is an odd
integral Number , return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- Ifexponent is an odd
- Ifexponent >
Assert :base isfinite and is neither+0 𝔽 nor-0 𝔽.- Ifexponent is
+∞ 𝔽, then - Ifexponent is
-∞ 𝔽, then Assert :exponent isfinite and is neither+0 𝔽 nor-0 𝔽.- Ifbase <
-0 𝔽 andexponent is not anintegral Number , returnNaN . - Return an
implementation-approximated Number value representing the result of raisingℝ (base) to theℝ (exponent) power.
The result ofbase**exponent whenbase is
6.1.6.1.4 Number::multiply (x,y )
The abstract operation Number::multiply takes argumentsx (a Number) andy (a Number) and returns a Number. It performs multiplication according to the rules of
- Ifx is
NaN ory isNaN , returnNaN . - Ifx is either
+∞ 𝔽 or-∞ 𝔽, then- Ify is either
+0 𝔽 or-0 𝔽, returnNaN . - Ify >
+0 𝔽, returnx. - Return -x.
- Ify is either
- Ify is either
+∞ 𝔽 or-∞ 𝔽, then- Ifx is either
+0 𝔽 or-0 𝔽, returnNaN . - Ifx >
+0 𝔽, returny. - Return -y.
- Ifx is either
- Ifx is
-0 𝔽, then- Ify is
-0 𝔽 ory <-0 𝔽, return+0 𝔽. - Else, return
-0 𝔽.
- Ify is
- Ify is
-0 𝔽, then- Ifx <
-0 𝔽, return+0 𝔽. - Else, return
-0 𝔽.
- Ifx <
- Return
𝔽 (ℝ (x) ×ℝ (y)).
6.1.6.1.5 Number::divide (x,y )
The abstract operation Number::divide takes argumentsx (a Number) andy (a Number) and returns a Number. It performs division according to the rules of
- Ifx is
NaN ory isNaN , returnNaN . - Ifx is either
+∞ 𝔽 or-∞ 𝔽, then- Ify is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Ify is
+0 𝔽 ory >+0 𝔽, returnx. - Return -x.
- Ify is either
- Ify is
+∞ 𝔽, then- Ifx is
+0 𝔽 orx >+0 𝔽, return+0 𝔽. Otherwise, return-0 𝔽.
- Ifx is
- Ify is
-∞ 𝔽, then- Ifx is
+0 𝔽 orx >+0 𝔽, return-0 𝔽. Otherwise, return+0 𝔽.
- Ifx is
- Ifx is either
+0 𝔽 or-0 𝔽, then- Ify is either
+0 𝔽 or-0 𝔽, returnNaN . - Ify >
+0 𝔽, returnx. - Return -x.
- Ify is either
- Ify is
+0 𝔽, then- Ifx >
+0 𝔽, return+∞ 𝔽. Otherwise, return-∞ 𝔽.
- Ifx >
- Ify is
-0 𝔽, then- Ifx >
+0 𝔽, return-∞ 𝔽. Otherwise, return+∞ 𝔽.
- Ifx >
- Return
𝔽 (ℝ (x) /ℝ (y)).
6.1.6.1.6 Number::remainder (n,d )
The abstract operation Number::remainder takes argumentsn (a Number) andd (a Number) and returns a Number. It yields the remainder from an implied division of its operands wheren is the dividend andd is the divisor. It performs the following steps when called:
- Ifn is
NaN ord isNaN , returnNaN . - Ifn is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Ifd is either
+∞ 𝔽 or-∞ 𝔽, returnn. - Ifd is either
+0 𝔽 or-0 𝔽, returnNaN . - Ifn is either
+0 𝔽 or-0 𝔽, returnn. Assert :n andd arefinite and non-zero.- Letquotient be
ℝ (n) /ℝ (d). - Letq be
truncate (quotient). - Letr be
ℝ (n) - (ℝ (d) ×q). - Ifr = 0 andn <
-0 𝔽, return-0 𝔽. - Return
𝔽 (r).
In C and C++, the remainder operator accepts only integral operands; in ECMAScript, it also accepts floating-point operands.
% operator is not the same as the “remainder” operation defined by% on floating-point operations to behave in a manner analogous to that of the Java6.1.6.1.7 Number::add (x,y )
The abstract operation Number::add takes argumentsx (a Number) andy (a Number) and returns a Number. It performs addition according to the rules of
6.1.6.1.8 Number::subtract (x,y )
The abstract operation Number::subtract takes argumentsx (a Number) andy (a Number) and returns a Number. It performs subtraction, producing the difference of its operands;x is the minuend andy is the subtrahend. It performs the following steps when called:
- Return
Number::add (x,Number::unaryMinus (y)).
It is always the case thatx - y produces the same result asx + (-y).
6.1.6.1.9 Number::leftShift (x,y )
The abstract operation Number::leftShift takes argumentsx (a Number) andy (a Number) and returns an
- Letlnum be !
ToInt32 (x). - Letrnum be !
ToUint32 (y). - LetshiftCount be
ℝ (rnum)modulo 32. - Return the result of left shiftinglnum byshiftCount bits. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.10 Number::signedRightShift (x,y )
The abstract operation Number::signedRightShift takes argumentsx (a Number) andy (a Number) and returns an
- Letlnum be !
ToInt32 (x). - Letrnum be !
ToUint32 (y). - LetshiftCount be
ℝ (rnum)modulo 32. - Return the result of performing a sign-extending right shift oflnum byshiftCount bits. The most significant bit is propagated. The
mathematical value of the result is exactly representable as a 32-bit two's complement bit string.
6.1.6.1.11 Number::unsignedRightShift (x,y )
The abstract operation Number::unsignedRightShift takes argumentsx (a Number) andy (a Number) and returns an
- Letlnum be !
ToUint32 (x). - Letrnum be !
ToUint32 (y). - LetshiftCount be
ℝ (rnum)modulo 32. - Return the result of performing a zero-filling right shift oflnum byshiftCount bits. Vacated bits are filled with zero. The
mathematical value of the result is exactly representable as a 32-bit unsigned bit string.
6.1.6.1.12 Number::lessThan (x,y )
The abstract operation Number::lessThan takes argumentsx (a Number) andy (a Number) and returns a Boolean or
- Ifx is
NaN , returnundefined . - Ify is
NaN , returnundefined . - Ifx isy, return
false . - Ifx is
+0 𝔽 andy is-0 𝔽, returnfalse . - Ifx is
-0 𝔽 andy is+0 𝔽, returnfalse . - Ifx is
+∞ 𝔽, returnfalse . - Ify is
+∞ 𝔽, returntrue . - Ify is
-∞ 𝔽, returnfalse . - Ifx is
-∞ 𝔽, returntrue . Assert :x andy arefinite .- If
ℝ (x) <ℝ (y), returntrue . Otherwise, returnfalse .
6.1.6.1.13 Number::equal (x,y )
The abstract operation Number::equal takes argumentsx (a Number) andy (a Number) and returns a Boolean. It performs the following steps when called:
- Ifx is
NaN , returnfalse . - Ify is
NaN , returnfalse . - Ifx isy, return
true . - Ifx is
+0 𝔽 andy is-0 𝔽, returntrue . - Ifx is
-0 𝔽 andy is+0 𝔽, returntrue . - Return
false .
6.1.6.1.14 Number::sameValue (x,y )
The abstract operation Number::sameValue takes argumentsx (a Number) andy (a Number) and returns a Boolean. It performs the following steps when called:
- Ifx is
NaN andy isNaN , returntrue . - Ifx is
+0 𝔽 andy is-0 𝔽, returnfalse . - Ifx is
-0 𝔽 andy is+0 𝔽, returnfalse . - Ifx isy, return
true . - Return
false .
6.1.6.1.15 Number::sameValueZero (x,y )
The abstract operation Number::sameValueZero takes argumentsx (a Number) andy (a Number) and returns a Boolean. It performs the following steps when called:
- Ifx is
NaN andy isNaN , returntrue . - Ifx is
+0 𝔽 andy is-0 𝔽, returntrue . - Ifx is
-0 𝔽 andy is+0 𝔽, returntrue . - Ifx isy, return
true . - Return
false .
6.1.6.1.16 NumberBitwiseOp (op,x,y )
The abstract operation NumberBitwiseOp takes argumentsop (&,^, or|),x (a Number), andy (a Number) and returns an
- Letlnum be !
ToInt32 (x). - Letrnum be !
ToInt32 (y). - Letlbits be the 32-bit two's complement bit string representing
ℝ (lnum). - Letrbits be the 32-bit two's complement bit string representing
ℝ (rnum). - Ifop is
&, then- Letresult be the result of applying the bitwise AND operation tolbits andrbits.
- Else ifop is
^, then- Letresult be the result of applying the bitwise exclusive OR (XOR) operation tolbits andrbits.
- Else,
Assert :op is|.- Letresult be the result of applying the bitwise inclusive OR operation tolbits andrbits.
- Return the
Number value for theinteger represented by the 32-bit two's complement bit stringresult.
6.1.6.1.17 Number::bitwiseAND (x,y )
The abstract operation Number::bitwiseAND takes argumentsx (a Number) andy (a Number) and returns an
- Return
NumberBitwiseOp (&,x,y).
6.1.6.1.18 Number::bitwiseXOR (x,y )
The abstract operation Number::bitwiseXOR takes argumentsx (a Number) andy (a Number) and returns an
- Return
NumberBitwiseOp (^,x,y).
6.1.6.1.19 Number::bitwiseOR (x,y )
The abstract operation Number::bitwiseOR takes argumentsx (a Number) andy (a Number) and returns an
- Return
NumberBitwiseOp (|,x,y).
6.1.6.1.20 Number::toString (x,radix )
The abstract operation Number::toString takes argumentsx (a Number) andradix (an
- Ifx is
NaN , return"NaN" . - Ifx is either
+0 𝔽 or-0 𝔽, return"0" . - Ifx <
-0 𝔽, return thestring-concatenation of"-" andNumber::toString (-x,radix). - Ifx is
+∞ 𝔽, return"Infinity" . - Letn,k, ands be
integers such thatk ≥ 1,radixk - 1 ≤s <radixk,𝔽 (s ×radixn -k) isx, andk is as small as possible. Note thatk is the number of digits in the representation ofs using radixradix, thats is not divisible byradix, and that the least significant digit ofs is not necessarily uniquely determined by these criteria. - Ifradix ≠ 10 orn is in the
inclusive interval from -5 to 21, then- Ifn ≥k, then
- Return the
string-concatenation of:- the code units of thek digits of the representation ofs using radixradix
- n -k occurrences of the code unit 0x0030 (DIGIT ZERO)
- Return the
- Else ifn > 0, then
- Return the
string-concatenation of:- the code units of the most significantn digits of the representation ofs using radixradix
- the code unit 0x002E (FULL STOP)
- the code units of the remainingk -n digits of the representation ofs using radixradix
- Return the
- Else,
Assert :n ≤ 0.- Return the
string-concatenation of:- the code unit 0x0030 (DIGIT ZERO)
- the code unit 0x002E (FULL STOP)
- -n occurrences of the code unit 0x0030 (DIGIT ZERO)
- the code units of thek digits of the representation ofs using radixradix
- Ifn ≥k, then
- NOTE: In this case, the input will be represented using scientific E notation, such as
1.2e+3. Assert :radix is 10.- Ifn < 0, then
- LetexponentSign be the code unit 0x002D (HYPHEN-MINUS).
- Else,
- LetexponentSign be the code unit 0x002B (PLUS SIGN).
- Ifk = 1, then
- Return the
string-concatenation of:- the code unit of the single digit ofs
- the code unit 0x0065 (LATIN SMALL LETTER E)
- exponentSign
- the code units of the decimal representation of
abs (n - 1)
- Return the
- Return the
string-concatenation of:- the code unit of the most significant digit of the decimal representation ofs
- the code unit 0x002E (FULL STOP)
- the code units of the remainingk - 1 digits of the decimal representation ofs
- the code unit 0x0065 (LATIN SMALL LETTER E)
- exponentSign
- the code units of the decimal representation of
abs (n - 1)
The following observations may be useful as guidelines for implementations, but are not part of the normative requirements of this Standard:
For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step
- Letn,k, ands be
integers such thatk ≥ 1,radixk - 1 ≤s <radixk,𝔽 (s ×radixn -k) isx, andk is as small as possible. If there are multiple possibilities fors, choose the value ofs for whichs ×radixn -k is closest in value toℝ (x). If there are two such possible values ofs, choose the one that is even. Note thatk is the number of digits in the representation ofs using radixradix and thats is not divisible byradix.
Implementers of ECMAScript may find useful the paper and code written by David M. Gay for binary-to-decimal conversion of floating-point numbers:
Gay, David M. Correctly Rounded Binary-Decimal and Decimal-Binary Conversions. Numerical Analysis, Manuscript 90-10. AT&T Bell Laboratories (Murray Hill, New Jersey). 30 November 1990. Available as
http://ampl.com/REFS/abstracts.html#rounding. Associated code available as
http://netlib.sandia.gov/fp/dtoa.c and as
http://netlib.sandia.gov/fp/g_fmt.c and may also be found at the variousnetlib mirror sites.
6.1.6.2 The BigInt Type
TheBigInt type represents an
6.1.6.2.1 BigInt::unaryMinus (x )
The abstract operation BigInt::unaryMinus takes argumentx (a BigInt) and returns a BigInt. It performs the following steps when called:
- Ifx is
0 ℤ, return0 ℤ. - Return -x.
6.1.6.2.2 BigInt::bitwiseNOT (x )
The abstract operation BigInt::bitwiseNOT takes argumentx (a BigInt) and returns a BigInt. It returns the one's complement ofx. It performs the following steps when called:
- Return -x -
1 ℤ.
6.1.6.2.3 BigInt::exponentiate (base,exponent )
The abstract operation BigInt::exponentiate takes argumentsbase (a BigInt) andexponent (a BigInt) and returns either a
- Ifexponent <
0 ℤ, throw aRangeError exception. - Ifbase is
0 ℤ andexponent is0 ℤ, return1 ℤ. - Returnbase raised to the powerexponent.
6.1.6.2.4 BigInt::multiply (x,y )
The abstract operation BigInt::multiply takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Returnx ×y.
6.1.6.2.5 BigInt::divide (x,y )
The abstract operation BigInt::divide takes argumentsx (a BigInt) andy (a BigInt) and returns either a
6.1.6.2.6 BigInt::remainder (n,d )
The abstract operation BigInt::remainder takes argumentsn (a BigInt) andd (a BigInt) and returns either a
6.1.6.2.7 BigInt::add (x,y )
The abstract operation BigInt::add takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Returnx +y.
6.1.6.2.8 BigInt::subtract (x,y )
The abstract operation BigInt::subtract takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Returnx -y.
6.1.6.2.9 BigInt::leftShift (x,y )
The abstract operation BigInt::leftShift takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
6.1.6.2.10 BigInt::signedRightShift (x,y )
The abstract operation BigInt::signedRightShift takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigInt::leftShift (x, -y).
6.1.6.2.11 BigInt::unsignedRightShift (x,y )
The abstract operation BigInt::unsignedRightShift takes argumentsx (a BigInt) andy (a BigInt) and returns a
- Throw a
TypeError exception.
6.1.6.2.12 BigInt::lessThan (x,y )
The abstract operation BigInt::lessThan takes argumentsx (a BigInt) andy (a BigInt) and returns a Boolean. It performs the following steps when called:
6.1.6.2.13 BigInt::equal (x,y )
The abstract operation BigInt::equal takes argumentsx (a BigInt) andy (a BigInt) and returns a Boolean. It performs the following steps when called:
6.1.6.2.14 BinaryAnd (x,y )
The abstract operation BinaryAnd takes argumentsx (0 or 1) andy (0 or 1) and returns 0 or 1. It performs the following steps when called:
- Ifx = 1 andy = 1, return 1.
- Else, return 0.
6.1.6.2.15 BinaryOr (x,y )
The abstract operation BinaryOr takes argumentsx (0 or 1) andy (0 or 1) and returns 0 or 1. It performs the following steps when called:
- Ifx = 1 ory = 1, return 1.
- Else, return 0.
6.1.6.2.16 BinaryXor (x,y )
The abstract operation BinaryXor takes argumentsx (0 or 1) andy (0 or 1) and returns 0 or 1. It performs the following steps when called:
- Ifx = 1 andy = 0, return 1.
- Else ifx = 0 andy = 1, return 1.
- Else, return 0.
6.1.6.2.17 BigIntBitwiseOp (op,x,y )
The abstract operation BigIntBitwiseOp takes argumentsop (&,^, or|),x (a BigInt), andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Setx to
ℝ (x). - Sety to
ℝ (y). - Letresult be 0.
- Letshift be 0.
- Repeat, until (x = 0 orx = -1) and (y = 0 ory = -1),
- Ifop is
&, then - Else ifop is
|, then - Else,
- Iftmp ≠ 0, then
- Setresult toresult - 2shift.
- NOTE: This extends the sign.
- Return the
BigInt value for result.
6.1.6.2.18 BigInt::bitwiseAND (x,y )
The abstract operation BigInt::bitwiseAND takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (&,x,y).
6.1.6.2.19 BigInt::bitwiseXOR (x,y )
The abstract operation BigInt::bitwiseXOR takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (^,x,y).
6.1.6.2.20 BigInt::bitwiseOR (x,y )
The abstract operation BigInt::bitwiseOR takes argumentsx (a BigInt) andy (a BigInt) and returns a BigInt. It performs the following steps when called:
- Return
BigIntBitwiseOp (|,x,y).
6.1.6.2.21 BigInt::toString (x,radix )
The abstract operation BigInt::toString takes argumentsx (a BigInt) andradix (an
- Ifx <
0 ℤ, return thestring-concatenation of"-" andBigInt::toString (-x,radix). - Return the String value consisting of the representation ofx using radixradix.
6.1.7 The Object Type
Each instance of theObject type, also referred to simply as “an Object”, represents a collection of properties. Each property is either a data property, or an accessor property:
- Adata property associates a key value with an
ECMAScript language value and a set of Boolean attributes. - Anaccessor property associates a key value with one or two accessor functions, and a set of Boolean attributes. The accessor functions are used to store or retrieve an
ECMAScript language value that is associated with the property.
The properties of an object are uniquely identified using property keys. Aproperty key is either a String or a Symbol. All Strings and Symbols, including the empty String, are valid as property keys. Aproperty name is a property key that
Aninteger index is a
Every non-negative
Property keys are used to access properties and their values. There are two kinds of access for properties:get andset, corresponding to value retrieval and assignment, respectively. The properties accessible via get and set access includes bothown properties that are a direct part of an object andinherited properties which are provided by another associated object via a property inheritance relationship. Inherited properties may be either own or inherited properties of the associated object. Each own property of an object must each have a key value that is distinct from the key values of the other own properties of that object.
All objects are logically collections of properties, but there are multiple forms of objects that differ in their semantics for accessing and manipulating their properties. Please see
In addition, some objects are callable; these are referred to as functions or
6.1.7.1 Property Attributes
Attributes are used in this specification to define and explain the state of Object properties as described in
| Attribute Name | Types of property for which it is present | Value Domain | Default Value | Description |
|---|---|---|---|---|
| [[Value]] | an | The value retrieved by a get access of the property. | ||
| [[Writable]] | a Boolean | If | ||
| [[Get]] | an Object or | If the value | ||
| [[Set]] | an Object or | If the value | ||
| [[Enumerable]] | a Boolean | If | ||
| [[Configurable]] | a Boolean | If |
6.1.7.2 Object Internal Methods and Internal Slots
The actual semantics of objects, in ECMAScript, are specified via algorithms calledinternal methods. Each object in an ECMAScript engine is associated with a set of internal methods that defines its runtime behaviour. These internal methods are not part of the ECMAScript language. They are defined by this specification purely for expository purposes. However, each object within an implementation of ECMAScript must behave as specified by the internal methods associated with it. The exact manner in which this is accomplished is determined by the implementation.
Internal method names are polymorphic. This means that different object values may perform different algorithms when a common internal method name is invoked upon them. That actual object upon which an internal method is invoked is the “target” of the invocation. If, at runtime, the implementation of an algorithm attempts to use an internal method of an object that the object does not support, a
Internal slots correspond to internal state that is associated with objects and used by various ECMAScript specification algorithms. Internal slots are not object properties and they are not inherited. Depending upon the specific internal slot specification, such state may consist of values of any
All objects have an internal slot named[[PrivateElements]], which is a
Internal methods and internal slots are identified within this specification using names enclosed in double square brackets [[ ]].
Anordinary object is an object that satisfies all of the following criteria:
- For the internal methods listed in
Table 4 , the object uses those defined in10.1 . - If the object has a[[Call]] internal method, it uses either the one defined in
10.2.1 or the one defined in10.3.1 . - If the object has a[[Construct]] internal method, it uses either the one defined in
10.2.2 or the one defined in10.3.2 .
Anexotic object is an object that is not an
This specification recognizes different kinds of
The “Signature” column of
In addition to its parameters, an internal method always has access to the object that is the target of the method invocation.
An internal method implicitly returns a
| Internal Method | Signature | Description |
|---|---|---|
| [[GetPrototypeOf]] | ( )→ Object | Null | Determine the object that provides inherited properties for this object. A |
| [[SetPrototypeOf]] | (Object | Null)→ Boolean | Associate this object with another object that provides inherited properties. Passing |
| [[IsExtensible]] | ( )→ Boolean | Determine whether it is permitted to add additional properties to this object. |
| [[PreventExtensions]] | ( )→ Boolean | Control whether new properties may be added to this object. Returns |
| [[GetOwnProperty]] | (propertyKey)→ Undefined | | Return a |
| [[DefineOwnProperty]] | (propertyKey,PropertyDescriptor)→ Boolean | Create or alter the own property, whose key ispropertyKey, to have the state described byPropertyDescriptor. Return |
| [[HasProperty]] | (propertyKey)→ Boolean | Return a Boolean value indicating whether this object already has either an own or inherited property whose key ispropertyKey. |
| [[Get]] | (propertyKey,Receiver)→any | Return the value of the property whose key ispropertyKey from this object. If any ECMAScript code must be executed to retrieve the property value,Receiver is used as the |
| [[Set]] | (propertyKey,value,Receiver)→ Boolean | Set the value of the property whose key ispropertyKey tovalue. If any ECMAScript code must be executed to set the property value,Receiver is used as the |
| [[Delete]] | (propertyKey)→ Boolean | Remove the own property whose key ispropertyKey from this object. Return |
| [[OwnPropertyKeys]] | ( )→ | Return a |
| Internal Method | Signature | Description |
|---|---|---|
| [[Call]] | (any, a | Executes code associated with this object. Invoked via a function call expression. The arguments to the internal method are a |
| [[Construct]] | (a | Creates an object. Invoked via thenew operator or asuper call. The first argument to the internal method is asuper call. The second argument is the object to which thenew operator was initially applied. Objects that implement this internal method are called |
The semantics of the essential internal methods for
6.1.7.3 Invariants of the Essential Internal Methods
The Internal Methods of Objects of an ECMAScript engine must conform to the list of invariants specified below. Ordinary ECMAScript Objects as well as all standard
Any implementation provided
An implementation must not allow these invariants to be circumvented in any manner such as by providing alternative interfaces that implement the functionality of the essential internal methods without enforcing their invariants.
Definitions:
- Thetarget of an internal method is the object upon which the internal method is called.
- A target isnon-extensible if it has been observed to return
false from its[[IsExtensible]] internal method, ortrue from its[[PreventExtensions]] internal method. - Anon-existent property is a property that does not exist as an own property on a non-extensible target.
- All references to
SameValue are according to the definition of theSameValue algorithm.
Return value:
The value returned by any internal method must be a
- [[Type]] =
normal ,[[Target]] =empty , and[[Value]] = a value of the "normal return type" shown below for that internal method, or - [[Type]] =
throw ,[[Target]] =empty , and[[Value]] = anyECMAScript language value .
An internal method must not return a
[[GetPrototypeOf]] ( )
- The normal return type is either Object or Null.
- If target is non-extensible, and[[GetPrototypeOf]] returns a valueV, then any future calls to[[GetPrototypeOf]] should return the
SameValue asV.
An object's prototype chain should have
[[SetPrototypeOf]] (V )
- The normal return type is Boolean.
- If target is non-extensible,[[SetPrototypeOf]] must return
false , unlessV is theSameValue as the target's observed[[GetPrototypeOf]] value.
[[IsExtensible]] ( )
- The normal return type is Boolean.
- If[[IsExtensible]] returns
false , all future calls to[[IsExtensible]] on the target must returnfalse .
[[PreventExtensions]] ( )
- The normal return type is Boolean.
- If[[PreventExtensions]] returns
true , all future calls to[[IsExtensible]] on the target must returnfalse and the target is now considered non-extensible.
[[GetOwnProperty]] (P )
- The normal return type is either
Property Descriptor or Undefined. - If the Type of the return value is
Property Descriptor , the return value must be afully populated Property Descriptor . - IfP is described as a non-configurable, non-writable own
data property , all future calls to[[GetOwnProperty]] (P ) must returnProperty Descriptor whose[[Value]] isSameValue asP's[[Value]] attribute. - IfP's attributes other than[[Writable]] and[[Value]] may change over time, or if the property might be deleted, thenP's[[Configurable]] attribute must be
true . - If the[[Writable]] attribute may change from
false totrue , then the[[Configurable]] attribute must betrue . - If the target is non-extensible andP is non-existent, then all future calls to[[GetOwnProperty]] (P) on the target must describeP as non-existent (i.e.[[GetOwnProperty]] (P) must return
undefined ).
As a consequence of the third invariant, if a property is described as a
[[DefineOwnProperty]] (P,Desc )
- The normal return type is Boolean.
- [[DefineOwnProperty]] must return
false ifP has previously been observed as a non-configurable own property of the target, unless either:- P is a writable
data property . A non-configurable writabledata property can be changed into a non-configurable non-writabledata property . - All attributes ofDesc are the
SameValue asP's attributes.
- P is a writable
- [[DefineOwnProperty]] (P,Desc) must return
false if target is non-extensible andP is a non-existent own property. That is, a non-extensible target object cannot be extended with new properties.
[[HasProperty]] (P )
- The normal return type is Boolean.
- IfP was previously observed as a non-configurable own data or
accessor property of the target,[[HasProperty]] must returntrue .
[[Get]] (P,Receiver )
- The normal return type is any
ECMAScript language type . - IfP was previously observed as a non-configurable, non-writable own
data property of the target with valueV, then[[Get]] must return theSameValue asV. - IfP was previously observed as a non-configurable own
accessor property of the target whose[[Get]] attribute isundefined , the[[Get]] operation must returnundefined .
[[Set]] (P,V,Receiver )
- The normal return type is Boolean.
- IfP was previously observed as a non-configurable, non-writable own
data property of the target, then[[Set]] must returnfalse unlessV is theSameValue asP's[[Value]] attribute. - IfP was previously observed as a non-configurable own
accessor property of the target whose[[Set]] attribute isundefined , the[[Set]] operation must returnfalse .
[[Delete]] (P )
- The normal return type is Boolean.
- IfP was previously observed as a non-configurable own data or
accessor property of the target,[[Delete]] must returnfalse .
[[OwnPropertyKeys]] ( )
- The normal return type is
List . - The returned
List must not contain any duplicate entries. - The Type of each element of the returned
List is either String or Symbol. - The returned
List must contain at least the keys of all non-configurable own properties that have previously been observed. - If the target is non-extensible, the returned
List must contain only the keys of all own properties of the target that are observable using[[GetOwnProperty]].
[[Call]] ( )
- The normal return type is any
ECMAScript language type .
[[Construct]] ( )
- The normal return type is Object.
- The target must also have a[[Call]] internal method.
6.1.7.4 Well-Known Intrinsic Objects
Well-known intrinsics are built-in objects that are explicitly referenced by the algorithms of this specification and which usually have
Within this specification a reference such as %name% means the intrinsic object, associated with the current
| Intrinsic Name | Global Name | ECMAScript Language Association |
|---|---|---|
AggregateError | TheAggregateError | |
Array | The Array | |
ArrayBuffer | The ArrayBuffer | |
| The prototype of Array iterator objects ( | ||
| The prototype of async-from-sync iterator objects ( | ||
| The | ||
| The | ||
| An object that all standard built-in async iterator objects indirectly inherit from | ||
Atomics | TheAtomics object ( | |
BigInt | The BigInt | |
BigInt64Array | The BigInt64Array | |
BigUint64Array | The BigUint64Array | |
Boolean | The Boolean | |
DataView | The DataView | |
Date | The Date | |
decodeURI | ThedecodeURI function ( | |
decodeURIComponent | ThedecodeURIComponent function ( | |
encodeURI | TheencodeURI function ( | |
encodeURIComponent | TheencodeURIComponent function ( | |
Error | The Error | |
eval | Theeval function ( | |
EvalError | The EvalError | |
FinalizationRegistry | The | |
Float32Array | The Float32Array | |
Float64Array | The Float64Array | |
| The prototype of For-In iterator objects ( | ||
Function | The Function | |
| The | ||
Int8Array | The Int8Array | |
Int16Array | The Int16Array | |
Int32Array | The Int32Array | |
isFinite | TheisFinite function ( | |
isNaN | TheisNaN function ( | |
| An object that all standard built-in iterator objects indirectly inherit from | ||
JSON | TheJSON object ( | |
Map | The Map | |
| The prototype of Map iterator objects ( | ||
Math | TheMath object ( | |
Number | The Number | |
Object | The Object | |
parseFloat | TheparseFloat function ( | |
parseInt | TheparseInt function ( | |
Promise | The Promise | |
Proxy | The Proxy | |
RangeError | The RangeError | |
ReferenceError | The ReferenceError | |
Reflect | TheReflect object ( | |
RegExp | The RegExp | |
| The prototype of RegExp String Iterator objects ( | ||
Set | The Set | |
| The prototype of Set iterator objects ( | ||
SharedArrayBuffer | The SharedArrayBuffer | |
String | The String | |
| The prototype of String iterator objects ( | ||
Symbol | The Symbol | |
SyntaxError | The SyntaxError | |
| A | ||
| The super class of all typed Array | ||
TypeError | The TypeError | |
Uint8Array | The Uint8Array | |
Uint8ClampedArray | The Uint8ClampedArray | |
Uint16Array | The Uint16Array | |
Uint32Array | The Uint32Array | |
URIError | The URIError | |
WeakMap | The WeakMap | |
WeakRef | The | |
WeakSet | The WeakSet |
Additional entries in
6.2 ECMAScript Specification Types
A specification type corresponds to meta-values that are used within algorithms to describe the semantics of ECMAScript language constructs and
6.2.1 The Enum Specification Type
Enums are values which are internal to the specification and not directly observable from ECMAScript code. Enums are denoted using a
6.2.2 The List and Record Specification Types
TheList type is used to explain the evaluation of argument lists (seenew expressions, in function calls, and in other algorithms where a simple ordered list of values is needed. Values of the List type are simply ordered sequences of list elements containing the individual values. These sequences may be of any length. The elements of a list may be randomly accessed using 0-origin indices. For notational convenience an array-like syntax can be used to access List elements. For example,arguments[2] is shorthand for saying the 3rd element of the Listarguments.
When an algorithm iterates over the elements of a List without specifying an order, the order used is the order of the elements in the List.
For notational convenience within this specification, a literal syntax can be used to express a new List value. For example, « 1, 2 » defines a List value that has two elements each of which is initialized to a specific value. A new empty List can be expressed as « ».
In this specification, the phrase "thelist-concatenation ofA,B, ..." (where each argument is a possibly empty List) denotes a new List value whose elements are the concatenation of the elements (in order) of each of the arguments (in order).
TheRecord type is used to describe data aggregations within the algorithms of this specification. A Record type value consists of one or more named fields. The value of each field is an
For notational convenience within this specification, an object literal-like syntax can be used to express a Record value. For example, {[[Field1]]: 42,[[Field2]]:
In specification text and algorithms, dot notation may be used to refer to a specific field of a Record value. For example, if R is the record shown in the previous paragraph then R.[[Field2]] is shorthand for “the field of R named[[Field2]]”.
Schema for commonly used Record field combinations may be named, and that name may be used as a prefix to a literal Record value to identify the specific kind of aggregations that is being described. For example: PropertyDescriptor {[[Value]]: 42,[[Writable]]:
6.2.3 The Set and Relation Specification Types
TheSet type is used to explain a collection of unordered elements for use in the
TheRelation type is used to explain constraints on Sets. Values of the Relation type are Sets of ordered pairs of values from its value domain. For example, a Relation on events is a set of ordered pairs of events. For a RelationR and two valuesa andb in the value domain ofR,aRb is shorthand for saying the ordered pair (a,b) is a member ofR. A Relation is least with respect to some conditions when it is the smallest Relation that satisfies those conditions.
Astrict partial order is a Relation valueR that satisfies the following.
For alla,b, andc inR's domain:
- It is not the case thataRa, and
- IfaRb andbRc, thenaRc.
The two properties above are called irreflexivity and transitivity, respectively.
Astrict total order is a Relation valueR that satisfies the following.
For alla,b, andc inR's domain:
- a isb oraRb orbRa, and
- It is not the case thataRa, and
- IfaRb andbRc, thenaRc.
The three properties above are called totality, irreflexivity, and transitivity, respectively.
6.2.4 The Completion Record Specification Type
TheCompletion Record specification type is used to explain the runtime propagation of values and control flow such as the behaviour of statements (break,continue,return andthrow) that perform nonlocal transfers of control.
Completion Records have the fields defined in
| Field Name | Value | Meaning |
|---|---|---|
| [[Type]] | The type of completion that occurred. | |
| [[Value]] | any value except a | The value that was produced. |
| [[Target]] | a String or | The target label for directed control transfers. |
The following shorthand terms are sometimes used to refer to Completion Records.
- normal completion refers to any Completion Record with a[[Type]] value of
normal . - break completion refers to any Completion Record with a[[Type]] value of
break . - continue completion refers to any Completion Record with a[[Type]] value of
continue . - return completion refers to any Completion Record with a[[Type]] value of
return . - throw completion refers to any Completion Record with a[[Type]] value of
throw . - abrupt completion refers to any Completion Record with a[[Type]] value other than
normal . - anormal completion containing some type of value refers to a normal completion that has a value of that type in its[[Value]] field.
Callable objects that are defined in this specification only return a normal completion or a throw completion. Returning any other kind of Completion Record is considered an editorial error.
6.2.4.1 NormalCompletion (value )
The abstract operation NormalCompletion takes argumentvalue (any value except a
- Return
Completion Record {[[Type]]:normal ,[[Value]]:value,[[Target]]:empty }.
6.2.4.2 ThrowCompletion (value )
The abstract operation ThrowCompletion takes argumentvalue (an
- Return
Completion Record {[[Type]]:throw ,[[Value]]:value,[[Target]]:empty }.
6.2.4.3 UpdateEmpty (completionRecord,value )
The abstract operation UpdateEmpty takes argumentscompletionRecord (a
Assert : IfcompletionRecord is either areturn completion or athrow completion , thencompletionRecord.[[Value]] is notempty .- IfcompletionRecord.[[Value]] is not
empty , return ? completionRecord. - Return
Completion Record {[[Type]]:completionRecord.[[Type]],[[Value]]:value,[[Target]]:completionRecord.[[Target]] }.
6.2.5 The Reference Record Specification Type
TheReference Record type is used to explain the behaviour of such operators asdelete,typeof, the assignment operators, thesuper
A Reference Record is a resolved name or property binding; its fields are defined by
| Field Name | Value | Meaning |
|---|---|---|
| [[Base]] | an | The value or |
| [[ReferencedName]] | a String, a Symbol, or a | The name of the binding. Always a String if[[Base]] value is an |
| [[Strict]] | a Boolean | |
| [[ThisValue]] | an | If notsuper |
The following
6.2.5.1 IsPropertyReference (V )
The abstract operation IsPropertyReference takes argumentV (a
- IfV.[[Base]] is
unresolvable , returnfalse . - IfV.[[Base]] is an
Environment Record , returnfalse ; otherwise returntrue .
6.2.5.2 IsUnresolvableReference (V )
The abstract operation IsUnresolvableReference takes argumentV (a
- IfV.[[Base]] is
unresolvable , returntrue ; otherwise returnfalse .
6.2.5.3 IsSuperReference (V )
The abstract operation IsSuperReference takes argumentV (a
- IfV.[[ThisValue]] is not
empty , returntrue ; otherwise returnfalse .
6.2.5.4 IsPrivateReference (V )
The abstract operation IsPrivateReference takes argumentV (a
- IfV.[[ReferencedName]] is a
Private Name , returntrue ; otherwise returnfalse .
6.2.5.5 GetValue (V )
The abstract operation GetValue takes argumentV (a
- IfV is not a
Reference Record , returnV. - If
IsUnresolvableReference (V) istrue , throw aReferenceError exception. - If
IsPropertyReference (V) istrue , then- LetbaseObj be ?
ToObject (V.[[Base]]). - If
IsPrivateReference (V) istrue , then- Return ?
PrivateGet (baseObj,V.[[ReferencedName]]).
- Return ?
- Return ? baseObj.[[Get]](V.[[ReferencedName]],
GetThisValue (V)).
- LetbaseObj be ?
- Else,
- Letbase beV.[[Base]].
Assert :base is anEnvironment Record .- Return ? base.GetBindingValue(V.[[ReferencedName]],V.[[Strict]]) (see
9.1 ).
The object that may be created in step
6.2.5.6 PutValue (V,W )
The abstract operation PutValue takes argumentsV (a
- IfV is not a
Reference Record , throw aReferenceError exception. - If
IsUnresolvableReference (V) istrue , then- IfV.[[Strict]] is
true , throw aReferenceError exception. - LetglobalObj be
GetGlobalObject (). - Perform ?
Set (globalObj,V.[[ReferencedName]],W,false ). - Return
unused .
- IfV.[[Strict]] is
- If
IsPropertyReference (V) istrue , then- LetbaseObj be ?
ToObject (V.[[Base]]). - If
IsPrivateReference (V) istrue , then- Return ?
PrivateSet (baseObj,V.[[ReferencedName]],W).
- Return ?
- Letsucceeded be ? baseObj.[[Set]](V.[[ReferencedName]],W,
GetThisValue (V)). - Ifsucceeded is
false andV.[[Strict]] istrue , throw aTypeError exception. - Return
unused .
- LetbaseObj be ?
- Else,
- Letbase beV.[[Base]].
Assert :base is anEnvironment Record .- Return ? base.SetMutableBinding(V.[[ReferencedName]],W,V.[[Strict]]) (see
9.1 ).
The object that may be created in step
6.2.5.7 GetThisValue (V )
The abstract operation GetThisValue takes argumentV (a
Assert :IsPropertyReference (V) istrue .- If
IsSuperReference (V) istrue , returnV.[[ThisValue]]; otherwise returnV.[[Base]].
6.2.5.8 InitializeReferencedBinding (V,W )
The abstract operation InitializeReferencedBinding takes argumentsV (a
Assert :IsUnresolvableReference (V) isfalse .- Letbase beV.[[Base]].
Assert :base is anEnvironment Record .- Return ? base.InitializeBinding(V.[[ReferencedName]],W).
6.2.5.9 MakePrivateReference (baseValue,privateIdentifier )
The abstract operation MakePrivateReference takes argumentsbaseValue (an
- LetprivEnv be the
running execution context 's PrivateEnvironment. Assert :privEnv is notnull .- LetprivateName be
ResolvePrivateIdentifier (privEnv,privateIdentifier). - Return the
Reference Record {[[Base]]:baseValue,[[ReferencedName]]:privateName,[[Strict]]:true ,[[ThisValue]]:empty }.
6.2.6 The Property Descriptor Specification Type
TheProperty Descriptor type is used to explain the manipulation and reification of Object property attributes. A Property Descriptor is a
Property Descriptor values may be further classified as data Property Descriptors and accessor Property Descriptors based upon the existence or use of certain fields. A data Property Descriptor is one that includes any fields named either[[Value]] or[[Writable]]. An accessor Property Descriptor is one that includes any fields named either[[Get]] or[[Set]]. Any Property Descriptor may have fields named[[Enumerable]] and[[Configurable]]. A Property Descriptor value may not be both a data Property Descriptor and an accessor Property Descriptor; however, it may be neither (in which case it is a generic Property Descriptor). Afully populated Property Descriptor is one that is either an accessor Property Descriptor or a data Property Descriptor and that has all of the corresponding fields defined in
The following
6.2.6.1 IsAccessorDescriptor (Desc )
The abstract operation IsAccessorDescriptor takes argumentDesc (a
- IfDesc is
undefined , returnfalse . - IfDesc has a[[Get]] field, return
true . - IfDesc has a[[Set]] field, return
true . - Return
false .
6.2.6.2 IsDataDescriptor (Desc )
The abstract operation IsDataDescriptor takes argumentDesc (a
- IfDesc is
undefined , returnfalse . - IfDesc has a[[Value]] field, return
true . - IfDesc has a[[Writable]] field, return
true . - Return
false .
6.2.6.3 IsGenericDescriptor (Desc )
The abstract operation IsGenericDescriptor takes argumentDesc (a
- IfDesc is
undefined , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - If
IsDataDescriptor (Desc) istrue , returnfalse . - Return
true .
6.2.6.4 FromPropertyDescriptor (Desc )
The abstract operation FromPropertyDescriptor takes argumentDesc (a
- IfDesc is
undefined , returnundefined . - Letobj be
OrdinaryObjectCreate (%Object.prototype% ). Assert :obj is an extensibleordinary object with no own properties.- IfDesc has a[[Value]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"value" ,Desc.[[Value]]).
- Perform !
- IfDesc has a[[Writable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"writable" ,Desc.[[Writable]]).
- Perform !
- IfDesc has a[[Get]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"get" ,Desc.[[Get]]).
- Perform !
- IfDesc has a[[Set]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"set" ,Desc.[[Set]]).
- Perform !
- IfDesc has an[[Enumerable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"enumerable" ,Desc.[[Enumerable]]).
- Perform !
- IfDesc has a[[Configurable]] field, then
- Perform !
CreateDataPropertyOrThrow (obj,"configurable" ,Desc.[[Configurable]]).
- Perform !
- Returnobj.
6.2.6.5 ToPropertyDescriptor (Obj )
The abstract operation ToPropertyDescriptor takes argumentObj (an
- IfObj
is not an Object , throw aTypeError exception. - Letdesc be a new
Property Descriptor that initially has no fields. - LethasEnumerable be ?
HasProperty (Obj,"enumerable" ). - IfhasEnumerable is
true , then - LethasConfigurable be ?
HasProperty (Obj,"configurable" ). - IfhasConfigurable is
true , then - LethasValue be ?
HasProperty (Obj,"value" ). - IfhasValue is
true , then- Letvalue be ?
Get (Obj,"value" ). - Setdesc.[[Value]] tovalue.
- Letvalue be ?
- LethasWritable be ?
HasProperty (Obj,"writable" ). - IfhasWritable is
true , then - LethasGet be ?
HasProperty (Obj,"get" ). - IfhasGet is
true , then- Letgetter be ?
Get (Obj,"get" ). - If
IsCallable (getter) isfalse andgetter is notundefined , throw aTypeError exception. - Setdesc.[[Get]] togetter.
- Letgetter be ?
- LethasSet be ?
HasProperty (Obj,"set" ). - IfhasSet is
true , then- Letsetter be ?
Get (Obj,"set" ). - If
IsCallable (setter) isfalse andsetter is notundefined , throw aTypeError exception. - Setdesc.[[Set]] tosetter.
- Letsetter be ?
- Ifdesc has a[[Get]] field ordesc has a[[Set]] field, then
- Ifdesc has a[[Value]] field ordesc has a[[Writable]] field, throw a
TypeError exception.
- Ifdesc has a[[Value]] field ordesc has a[[Writable]] field, throw a
- Returndesc.
6.2.6.6 CompletePropertyDescriptor (Desc )
The abstract operation CompletePropertyDescriptor takes argumentDesc (a
- Letlike be the
Record {[[Value]]:undefined ,[[Writable]]:false ,[[Get]]:undefined ,[[Set]]:undefined ,[[Enumerable]]:false ,[[Configurable]]:false }. - If
IsGenericDescriptor (Desc) istrue orIsDataDescriptor (Desc) istrue , then- IfDesc does not have a[[Value]] field, setDesc.[[Value]] tolike.[[Value]].
- IfDesc does not have a[[Writable]] field, setDesc.[[Writable]] tolike.[[Writable]].
- Else,
- IfDesc does not have a[[Get]] field, setDesc.[[Get]] tolike.[[Get]].
- IfDesc does not have a[[Set]] field, setDesc.[[Set]] tolike.[[Set]].
- IfDesc does not have an[[Enumerable]] field, setDesc.[[Enumerable]] tolike.[[Enumerable]].
- IfDesc does not have a[[Configurable]] field, setDesc.[[Configurable]] tolike.[[Configurable]].
- Return
unused .
6.2.7 The Environment Record Specification Type
The
6.2.8 The Abstract Closure Specification Type
TheAbstract Closure specification type is used to refer to algorithm steps together with a collection of values. Abstract Closures are meta-values and are invoked using function application style such asclosure(arg1,arg2). Like
In algorithm steps that create an Abstract Closure, values are captured with the verb "capture" followed by a list of aliases. When an Abstract Closure is created, it captures the value that is associated with each alias at that time. In steps that specify the algorithm to be performed when an Abstract Closure is called, each captured value is referred to by the alias that was used to capture the value.
If an Abstract Closure returns a
Abstract Closures are created inline as part of other algorithms, shown in the following example.
- Letaddend be 41.
- Letclosure be a new
Abstract Closure with parameters (x) that capturesaddend and performs the following steps when called:- Returnx +addend.
- Letval beclosure(1).
Assert :val is 42.
6.2.9 Data Blocks
TheData Block specification type is used to describe a distinct and mutable sequence of byte-sized (8 bit) numeric values. Abyte value is an
For notational convenience within this specification, an array-like syntax can be used to access the individual bytes of a Data Block value. This notation presents a Data Block value as a 0-origined
A data block that resides in memory that can be referenced from multiple
The semantics of Shared Data Blocks is defined using
The following
6.2.9.1 CreateByteDataBlock (size )
The abstract operation CreateByteDataBlock takes argumentsize (a non-negative
- Ifsize > 253 - 1, throw a
RangeError exception. - Letdb be a new
Data Block value consisting ofsize bytes. If it is impossible to create such aData Block , throw aRangeError exception. - Set all of the bytes ofdb to 0.
- Returndb.
6.2.9.2 CreateSharedByteDataBlock (size )
The abstract operation CreateSharedByteDataBlock takes argumentsize (a non-negative
- Letdb be a new
Shared Data Block value consisting ofsize bytes. If it is impossible to create such aShared Data Block , throw aRangeError exception. - Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - Letzero be « 0 ».
- For each indexi ofdb, do
- Append
WriteSharedMemory {[[Order]]:init ,[[NoTear]]:true ,[[Block]]:db,[[ByteIndex]]:i,[[ElementSize]]: 1,[[Payload]]:zero } toeventsRecord.[[EventList]].
- Append
- Returndb.
6.2.9.3 CopyDataBlockBytes (toBlock,toIndex,fromBlock,fromIndex,count )
The abstract operation CopyDataBlockBytes takes argumentstoBlock (a
Assert :fromBlock andtoBlock are distinct values.- LetfromSize be the number of bytes infromBlock.
Assert :fromIndex +count ≤fromSize.- LettoSize be the number of bytes intoBlock.
Assert :toIndex +count ≤toSize.- Repeat, whilecount > 0,
- IffromBlock is a
Shared Data Block , then- Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - Letbytes be a
List whose sole element is a nondeterministically chosenbyte value . - NOTE: In implementations,bytes is the result of a non-atomic read instruction on the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - LetreadEvent be
ReadSharedMemory {[[Order]]:unordered ,[[NoTear]]:true ,[[Block]]:fromBlock,[[ByteIndex]]:fromIndex,[[ElementSize]]: 1 }. - AppendreadEvent toeventsRecord.[[EventList]].
- Append
Chosen Value Record {[[Event]]:readEvent,[[ChosenValue]]:bytes } toexecution.[[ChosenValues]]. - IftoBlock is a
Shared Data Block , then- Append
WriteSharedMemory {[[Order]]:unordered ,[[NoTear]]:true ,[[Block]]:toBlock,[[ByteIndex]]:toIndex,[[ElementSize]]: 1,[[Payload]]:bytes } toeventsRecord.[[EventList]].
- Append
- Else,
- SettoBlock[toIndex] tobytes[0].
- Letexecution be the[[CandidateExecution]] field of the
- Else,
Assert :toBlock is not aShared Data Block .- SettoBlock[toIndex] tofromBlock[fromIndex].
- SettoIndex totoIndex + 1.
- SetfromIndex tofromIndex + 1.
- Setcount tocount - 1.
- IffromBlock is a
- Return
unused .
6.2.10 The PrivateElement Specification Type
The PrivateElement type is a
Values of the PrivateElement type are
| Field Name | Values of the[[Kind]] field for which it is present | Value | Meaning |
|---|---|---|---|
| [[Key]] | All | a | The name of the field, method, or accessor. |
| [[Kind]] | All | The kind of the element. | |
| [[Value]] | an | The value of the field. | |
| [[Get]] | a | The getter for a private accessor. | |
| [[Set]] | a | The setter for a private accessor. |
6.2.11 The ClassFieldDefinition Record Specification Type
The ClassFieldDefinition type is a
Values of the ClassFieldDefinition type are
| Field Name | Value | Meaning |
|---|---|---|
| [[Name]] | a | The name of the field. |
| [[Initializer]] | an ECMAScript | The initializer of the field, if any. |
6.2.12 Private Names
ThePrivate Name specification type is used to describe a globally unique value (one which differs from any other Private Name, even if they are otherwise indistinguishable) which represents the key of a private class element (field, method, or accessor). Each Private Name has an associated immutable[[Description]] which
6.2.13 The ClassStaticBlockDefinition Record Specification Type
AClassStaticBlockDefinition Record is a
ClassStaticBlockDefinition Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[BodyFunction]] | an ECMAScript | The |
7 Abstract Operations
These operations are not a part of the ECMAScript language; they are defined here solely to aid the specification of the semantics of the ECMAScript language. Other, more specialized
7.1 Type Conversion
The ECMAScript language implicitly performs automatic type conversion as needed. To clarify the semantics of certain constructs it is useful to define a set of conversion
The
7.1.1 ToPrimitive (input [ ,preferredType ] )
The abstract operation ToPrimitive takes argumentinput (an
- Ifinput
is an Object , then- LetexoticToPrim be ?
GetMethod (input,@@toPrimitive ). - IfexoticToPrim is not
undefined , then- IfpreferredType is not present, then
- Lethint be
"default" .
- Lethint be
- Else ifpreferredType is
string , then- Lethint be
"string" .
- Lethint be
- Else,
Assert :preferredType isnumber .- Lethint be
"number" .
- Letresult be ?
Call (exoticToPrim,input, «hint »). - Ifresult
is not an Object , returnresult. - Throw a
TypeError exception.
- IfpreferredType is not present, then
- IfpreferredType is not present, letpreferredType be
number . - Return ?
OrdinaryToPrimitive (input,preferredType).
- LetexoticToPrim be ?
- Returninput.
When ToPrimitive is called without a hint, then it generally behaves as if the hint were
7.1.1.1 OrdinaryToPrimitive (O,hint )
The abstract operation OrdinaryToPrimitive takes argumentsO (an Object) andhint (
- Ifhint is
string , then- LetmethodNames be «
"toString" ,"valueOf" ».
- LetmethodNames be «
- Else,
- LetmethodNames be «
"valueOf" ,"toString" ».
- LetmethodNames be «
- For each elementname ofmethodNames, do
- Letmethod be ?
Get (O,name). - If
IsCallable (method) istrue , then- Letresult be ?
Call (method,O). - Ifresult
is not an Object , returnresult.
- Letresult be ?
- Letmethod be ?
- Throw a
TypeError exception.
7.1.2 ToBoolean (argument )
The abstract operation ToBoolean takes argumentargument (an
- Ifargument
is a Boolean , returnargument. - Ifargument is one of
undefined ,null ,+0 𝔽,-0 𝔽,NaN ,0 ℤ, or the empty String, returnfalse . - NOTE: This step is replaced in section
B.3.6.1 . - Return
true .
7.1.3 ToNumeric (value )
The abstract operation ToNumeric takes argumentvalue (an
- LetprimValue be ?
ToPrimitive (value,number ). - IfprimValue
is a BigInt , returnprimValue. - Return ?
ToNumber (primValue).
7.1.4 ToNumber (argument )
The abstract operation ToNumber takes argumentargument (an
- Ifargument
is a Number , returnargument. - Ifargument is either a Symbol or a BigInt, throw a
TypeError exception. - Ifargument is
undefined , returnNaN . - Ifargument is either
null orfalse , return+0 𝔽. - Ifargument is
true , return1 𝔽. - Ifargument
is a String , returnStringToNumber (argument). Assert :argumentis an Object .- LetprimValue be ?
ToPrimitive (argument,number ). Assert :primValueis not an Object .- Return ?
ToNumber (primValue).
7.1.4.1 ToNumber Applied to the String Type
The abstract operation
Syntax
All grammar symbols not explicitly defined above have the definitions used in the Lexical Grammar for numeric literals (
Some differences should be noted between the syntax of a
- A
StringNumericLiteral may include leading and/or trailing white space and/or line terminators. - A
StringNumericLiteral that is decimal may have any number of leading0digits. - A
StringNumericLiteral that is decimal may include a+or-to indicate its sign. - A
StringNumericLiteral that is empty or contains only white space is converted to+0 𝔽. Infinityand-Infinityare recognized as aStringNumericLiteral but not as aNumericLiteral .- A
StringNumericLiteral cannot include aBigIntLiteralSuffix . - A
StringNumericLiteral cannot include aNumericLiteralSeparator .
7.1.4.1.1 StringToNumber (str )
The abstract operation StringToNumber takes argumentstr (a String) and returns a Number. It performs the following steps when called:
- Lettext be
StringToCodePoints (str). - Letliteral be
ParseText (text,StringNumericLiteral ). - Ifliteral is a
List of errors, returnNaN . - Return
StringNumericValue ofliteral.
7.1.4.1.2 Runtime Semantics: StringNumericValue
The
The conversion of a
It is defined piecewise over the following productions:
- Return
+0 𝔽.
- Return
StringNumericValue ofStrNumericLiteral .
- Return
𝔽 (MV ofNonDecimalIntegerLiteral ).
- Leta be
StringNumericValue ofStrUnsignedDecimalLiteral . - Ifa is
+0 𝔽, return-0 𝔽. - Return -a.
- Return
+∞ 𝔽.
- Leta be MV of the first
DecimalDigits . - If the second
DecimalDigits is present, then- Letb be MV of the second
DecimalDigits . - Letn be the number of code points in the second
DecimalDigits .
- Letb be MV of the second
- Else,
- Letb be 0.
- Letn be 0.
- If
ExponentPart is present, lete be MV ofExponentPart . Otherwise, lete be 0. - Return
RoundMVResult ((a + (b × 10-n)) × 10e).
- Letb be MV of
DecimalDigits . - If
ExponentPart is present, lete be MV ofExponentPart . Otherwise, lete be 0. - Letn be the number of code points in
DecimalDigits . - Return
RoundMVResult (b × 10e -n).
- Leta be MV of
DecimalDigits . - If
ExponentPart is present, lete be MV ofExponentPart . Otherwise, lete be 0. - Return
RoundMVResult (a × 10e).
7.1.4.1.3 RoundMVResult (n )
The abstract operation RoundMVResult takes argumentn (a
- If the decimal representation ofn has 20 or fewer significant digits, return
𝔽 (n). - Letoption1 be the
mathematical value denoted by the result of replacing each significant digit in the decimal representation ofn after the 20th with a 0 digit. - Letoption2 be the
mathematical value denoted by the result of replacing each significant digit in the decimal representation ofn after the 20th with a 0 digit and then incrementing it at the 20th position (with carrying as necessary). - Letchosen be an
implementation-defined choice of eitheroption1 oroption2. - Return
𝔽 (chosen).
7.1.5 ToIntegerOrInfinity (argument )
The abstract operation ToIntegerOrInfinity takes argumentargument (an
7.1.6 ToInt32 (argument )
The abstract operation ToInt32 takes argumentargument (an
Given the above definition of ToInt32:
- The ToInt32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
- ToInt32(
ToUint32 (x)) is the same value as ToInt32(x) for all values ofx. (It is to preserve this latter property that+∞ 𝔽 and-∞ 𝔽 are mapped to+0 𝔽.) - ToInt32 maps
-0 𝔽 to+0 𝔽.
7.1.7 ToUint32 (argument )
The abstract operation ToUint32 takes argumentargument (an
Given the above definition of ToUint32:
- Step
5 is the only difference between ToUint32 andToInt32 . - The ToUint32 abstract operation is idempotent: if applied to a result that it produced, the second application leaves that value unchanged.
- ToUint32(
ToInt32 (x)) is the same value as ToUint32(x) for all values ofx. (It is to preserve this latter property that+∞ 𝔽 and-∞ 𝔽 are mapped to+0 𝔽.) - ToUint32 maps
-0 𝔽 to+0 𝔽.
7.1.8 ToInt16 (argument )
The abstract operation ToInt16 takes argumentargument (an
7.1.9 ToUint16 (argument )
The abstract operation ToUint16 takes argumentargument (an
7.1.10 ToInt8 (argument )
The abstract operation ToInt8 takes argumentargument (an
7.1.11 ToUint8 (argument )
The abstract operation ToUint8 takes argumentargument (an
7.1.12 ToUint8Clamp (argument )
The abstract operation ToUint8Clamp takes argumentargument (an
- Letnumber be ?
ToNumber (argument). - Ifnumber is
NaN , return+0 𝔽. - Letmv be the
extended mathematical value of number. - Letclamped be the result of
clamping mv between 0 and 255. - Letf be
floor (clamped). - Ifclamped <f + 0.5, return
𝔽 (f). - Ifclamped >f + 0.5, return
𝔽 (f + 1). - Iff is even, return
𝔽 (f). Otherwise, return𝔽 (f + 1).
Unlike most other ECMAScriptMath.round
7.1.13 ToBigInt (argument )
The abstract operation ToBigInt takes argumentargument (an
- Letprim be ?
ToPrimitive (argument,number ). - Return the value thatprim corresponds to in
Table 12 .
| Argument Type | Result |
|---|---|
| Undefined | Throw a |
| Null | Throw a |
| Boolean | Return1n ifprim is0n ifprim is |
| BigInt | Returnprim. |
| Number | Throw a |
| String |
|
| Symbol | Throw a |
7.1.14 StringToBigInt (str )
The abstract operation StringToBigInt takes argumentstr (a String) and returns a BigInt or
- Lettext be
StringToCodePoints (str). - Letliteral be
ParseText (text,StringIntegerLiteral ). - Ifliteral is a
List of errors, returnundefined . - Letmv be the MV ofliteral.
Assert :mv is aninteger .- Return
ℤ (mv).
7.1.14.1 StringIntegerLiteral Grammar
Syntax
7.1.14.2 Runtime Semantics: MV
- The MV of
StringIntegerLiteral ::: StrWhiteSpace opt - The MV of
StringIntegerLiteral ::: StrWhiteSpace opt StrIntegerLiteral StrWhiteSpace opt StrIntegerLiteral .
7.1.15 ToBigInt64 (argument )
The abstract operation ToBigInt64 takes argumentargument (an
7.1.16 ToBigUint64 (argument )
The abstract operation ToBigUint64 takes argumentargument (an
7.1.17 ToString (argument )
The abstract operation ToString takes argumentargument (an
- Ifargument
is a String , returnargument. - Ifargument
is a Symbol , throw aTypeError exception. - Ifargument is
undefined , return"undefined" . - Ifargument is
null , return"null" . - Ifargument is
true , return"true" . - Ifargument is
false , return"false" . - Ifargument
is a Number , returnNumber::toString (argument, 10). - Ifargument
is a BigInt , returnBigInt::toString (argument, 10). Assert :argumentis an Object .- LetprimValue be ?
ToPrimitive (argument,string ). Assert :primValueis not an Object .- Return ?
ToString (primValue).
7.1.18 ToObject (argument )
The abstract operation ToObject takes argumentargument (an
| Argument Type | Result |
|---|---|
| Undefined | Throw a |
| Null | Throw a |
| Boolean | Return a new Boolean object whose[[BooleanData]] internal slot is set toargument. See |
| Number | Return a new Number object whose[[NumberData]] internal slot is set toargument. See |
| String | Return a new String object whose[[StringData]] internal slot is set toargument. See |
| Symbol | Return a new Symbol object whose[[SymbolData]] internal slot is set toargument. See |
| BigInt | Return a new BigInt object whose[[BigIntData]] internal slot is set toargument. See |
| Object | Returnargument. |
7.1.19 ToPropertyKey (argument )
The abstract operation ToPropertyKey takes argumentargument (an
- Letkey be ?
ToPrimitive (argument,string ). - Ifkey
is a Symbol , then- Returnkey.
- Return !
ToString (key).
7.1.20 ToLength (argument )
The abstract operation ToLength takes argumentargument (an
- Letlen be ?
ToIntegerOrInfinity (argument). - Iflen ≤ 0, return
+0 𝔽. - Return
𝔽 (min (len, 253 - 1)).
7.1.21 CanonicalNumericIndexString (argument )
The abstract operation CanonicalNumericIndexString takes argumentargument (a String) and returns a Number or
Acanonical numeric string is any String value for which the CanonicalNumericIndexString abstract operation does not return
7.1.22 ToIndex (value )
The abstract operation ToIndex takes argumentvalue (an
- Letinteger be ?
ToIntegerOrInfinity (value). - Ifinteger is not in the
inclusive interval from 0 to 253 - 1, throw aRangeError exception. - Returninteger.
7.2 Testing and Comparison Operations
7.2.1 RequireObjectCoercible (argument )
The abstract operation RequireObjectCoercible takes argumentargument (an
| Argument Type | Result |
|---|---|
| Undefined | Throw a |
| Null | Throw a |
| Boolean | Returnargument. |
| Number | Returnargument. |
| String | Returnargument. |
| Symbol | Returnargument. |
| BigInt | Returnargument. |
| Object | Returnargument. |
7.2.2 IsArray (argument )
The abstract operation IsArray takes argumentargument (an
- Ifargument
is not an Object , returnfalse . - Ifargument is an
Array exotic object , returntrue . - Ifargument is a
Proxy exotic object , then- Perform ?
ValidateNonRevokedProxy (argument). - LetproxyTarget beargument.[[ProxyTarget]].
- Return ?
IsArray (proxyTarget).
- Perform ?
- Return
false .
7.2.3 IsCallable (argument )
The abstract operation IsCallable takes argumentargument (an
- Ifargument
is not an Object , returnfalse . - Ifargument has a[[Call]] internal method, return
true . - Return
false .
7.2.4 IsConstructor (argument )
The abstract operation IsConstructor takes argumentargument (an
- Ifargument
is not an Object , returnfalse . - Ifargument has a[[Construct]] internal method, return
true . - Return
false .
7.2.5 IsExtensible (O )
The abstract operation IsExtensible takes argumentO (an Object) and returns either a
- Return ? O.[[IsExtensible]]().
7.2.6 IsIntegralNumber (argument )
The abstract operation IsIntegralNumber takes argumentargument (an
- Ifargument
is not a Number , returnfalse . - Ifargument is not
finite , returnfalse . - If
truncate (ℝ (argument)) ≠ℝ (argument), returnfalse . - Return
true .
7.2.7 IsPropertyKey (argument )
The abstract operation IsPropertyKey takes argumentargument (an
- Ifargument
is a String , returntrue . - Ifargument
is a Symbol , returntrue . - Return
false .
7.2.8 IsRegExp (argument )
The abstract operation IsRegExp takes argumentargument (an
- Ifargument
is not an Object , returnfalse . - Letmatcher be ?
Get (argument,@@match ). - Ifmatcher is not
undefined , returnToBoolean (matcher). - Ifargument has a[[RegExpMatcher]] internal slot, return
true . - Return
false .
7.2.9 Static Semantics: IsStringWellFormedUnicode (string )
The abstract operation IsStringWellFormedUnicode takes argumentstring (a String) and returns a Boolean. It interpretsstring as a sequence of UTF-16 encoded code points, as described in
- Letlen be the length ofstring.
- Letk be 0.
- Repeat, whilek <len,
- Letcp be
CodePointAt (string,k). - Ifcp.[[IsUnpairedSurrogate]] is
true , returnfalse . - Setk tok +cp.[[CodeUnitCount]].
- Letcp be
- Return
true .
7.2.10 SameValue (x,y )
The abstract operation SameValue takes argumentsx (an
- If
Type (x) is notType (y), returnfalse . - Ifx
is a Number , then- Return
Number::sameValue (x,y).
- Return
- Return
SameValueNonNumber (x,y).
This algorithm differs from the
7.2.11 SameValueZero (x,y )
The abstract operation SameValueZero takes argumentsx (an
- If
Type (x) is notType (y), returnfalse . - Ifx
is a Number , then- Return
Number::sameValueZero (x,y).
- Return
- Return
SameValueNonNumber (x,y).
SameValueZero differs from
7.2.12 SameValueNonNumber (x,y )
The abstract operation SameValueNonNumber takes argumentsx (an
Assert :Type (x) isType (y).- Ifx is either
null orundefined , returntrue . - Ifx
is a BigInt , then- Return
BigInt::equal (x,y).
- Return
- Ifx
is a String , then- Ifx andy have the same length and the same code units in the same positions, return
true ; otherwise, returnfalse .
- Ifx andy have the same length and the same code units in the same positions, return
- Ifx
is a Boolean , then- Ifx andy are both
true or bothfalse , returntrue ; otherwise, returnfalse .
- Ifx andy are both
- NOTE: All other
ECMAScript language values are compared by identity. - Ifx isy, return
true ; otherwise, returnfalse .
7.2.13 IsLessThan (x,y,LeftFirst )
The abstract operation IsLessThan takes argumentsx (an
- IfLeftFirst is
true , then- Letpx be ?
ToPrimitive (x,number ). - Letpy be ?
ToPrimitive (y,number ).
- Letpx be ?
- Else,
- NOTE: The order of evaluation needs to be reversed to preserve left to right evaluation.
- Letpy be ?
ToPrimitive (y,number ). - Letpx be ?
ToPrimitive (x,number ).
- Ifpx
is a String andpyis a String , then- Letlx be the length ofpx.
- Letly be the length ofpy.
- For each
integer i such that 0 ≤i <min (lx,ly), in ascending order, do- Letcx be the numeric value of the code unit at indexi withinpx.
- Letcy be the numeric value of the code unit at indexi withinpy.
- Ifcx <cy, return
true . - Ifcx >cy, return
false .
- Iflx <ly, return
true . Otherwise, returnfalse .
- Else,
- Ifpx
is a BigInt andpyis a String , then- Letny be
StringToBigInt (py). - Ifny is
undefined , returnundefined . - Return
BigInt::lessThan (px,ny).
- Letny be
- Ifpx
is a String andpyis a BigInt , then- Letnx be
StringToBigInt (px). - Ifnx is
undefined , returnundefined . - Return
BigInt::lessThan (nx,py).
- Letnx be
- NOTE: Becausepx andpy are primitive values, evaluation order is not important.
- Letnx be ?
ToNumeric (px). - Letny be ?
ToNumeric (py). - If
Type (nx) isType (ny), then- Ifnx
is a Number , then- Return
Number::lessThan (nx,ny).
- Return
- Else,
Assert :nxis a BigInt .- Return
BigInt::lessThan (nx,ny).
- Ifnx
Assert :nxis a BigInt andnyis a Number , ornxis a Number andnyis a BigInt .- Ifnx orny is
NaN , returnundefined . - Ifnx is
-∞ 𝔽 orny is+∞ 𝔽, returntrue . - Ifnx is
+∞ 𝔽 orny is-∞ 𝔽, returnfalse . - If
ℝ (nx) <ℝ (ny), returntrue ; otherwise returnfalse .
- Ifpx
The comparison of Strings uses a simple lexicographic ordering on sequences of UTF-16 code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore String values that are canonically equal according to the Unicode Standard but not in the same normalization form could test as unequal. Also note that lexicographic ordering bycode unit differs from ordering bycode point for Strings containing
7.2.14 IsLooselyEqual (x,y )
The abstract operation IsLooselyEqual takes argumentsx (an== operator. It performs the following steps when called:
- If
Type (x) isType (y), then- Return
IsStrictlyEqual (x,y).
- Return
- Ifx is
null andy isundefined , returntrue . - Ifx is
undefined andy isnull , returntrue . - NOTE: This step is replaced in section
B.3.6.2 . - Ifx
is a Number andyis a String , return !IsLooselyEqual (x, !ToNumber (y)). - Ifx
is a String andyis a Number , return !IsLooselyEqual (!ToNumber (x),y). - Ifx
is a BigInt andyis a String , then- Letn be
StringToBigInt (y). - Ifn is
undefined , returnfalse . - Return !
IsLooselyEqual (x,n).
- Letn be
- Ifx
is a String andyis a BigInt , return !IsLooselyEqual (y,x). - Ifx
is a Boolean , return !IsLooselyEqual (!ToNumber (x),y). - Ify
is a Boolean , return !IsLooselyEqual (x, !ToNumber (y)). - Ifx is either a String, a Number, a BigInt, or a Symbol andy
is an Object , return !IsLooselyEqual (x, ?ToPrimitive (y)). - Ifx
is an Object andy is either a String, a Number, a BigInt, or a Symbol, return !IsLooselyEqual (?ToPrimitive (x),y). - Ifx
is a BigInt andyis a Number , or ifxis a Number andyis a BigInt , then - Return
false .
7.2.15 IsStrictlyEqual (x,y )
The abstract operation IsStrictlyEqual takes argumentsx (an=== operator. It performs the following steps when called:
- If
Type (x) is notType (y), returnfalse . - Ifx
is a Number , then- Return
Number::equal (x,y).
- Return
- Return
SameValueNonNumber (x,y).
This algorithm differs from the
7.3 Operations on Objects
7.3.1 MakeBasicObject (internalSlotsList )
The abstract operation MakeBasicObject takes argumentinternalSlotsList (a
- Letobj be a newly created object with an internal slot for each name ininternalSlotsList.
- Setobj's essential internal methods to the default
ordinary object definitions specified in10.1 . Assert : If the caller will not be overriding bothobj's[[GetPrototypeOf]] and[[SetPrototypeOf]] essential internal methods, theninternalSlotsList contains[[Prototype]].Assert : If the caller will not be overriding all ofobj's[[SetPrototypeOf]],[[IsExtensible]], and[[PreventExtensions]] essential internal methods, theninternalSlotsList contains[[Extensible]].- IfinternalSlotsList contains[[Extensible]], setobj.[[Extensible]] to
true . - Returnobj.
Within this specification,
7.3.2 Get (O,P )
The abstract operation Get takes argumentsO (an Object) andP (a
- Return ? O.[[Get]](P,O).
7.3.3 GetV (V,P )
The abstract operation GetV takes argumentsV (an
- LetO be ?
ToObject (V). - Return ? O.[[Get]](P,V).
7.3.4 Set (O,P,V,Throw )
The abstract operation Set takes argumentsO (an Object),P (a
- Letsuccess be ? O.[[Set]](P,V,O).
- Ifsuccess is
false andThrow istrue , throw aTypeError exception. - Return
unused .
7.3.5 CreateDataProperty (O,P,V )
The abstract operation CreateDataProperty takes argumentsO (an Object),P (a
- LetnewDesc be the PropertyDescriptor {[[Value]]:V,[[Writable]]:
true ,[[Enumerable]]:true ,[[Configurable]]:true }. - Return ? O.[[DefineOwnProperty]](P,newDesc).
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or ifO is not extensible,[[DefineOwnProperty]] will return
7.3.6 CreateDataPropertyOrThrow (O,P,V )
The abstract operation CreateDataPropertyOrThrow takes argumentsO (an Object),P (a
- Letsuccess be ?
CreateDataProperty (O,P,V). - Ifsuccess is
false , throw aTypeError exception. - Return
unused .
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator. Normally, the property will not already exist. If it does exist and is not configurable or ifO is not extensible,[[DefineOwnProperty]] will return
7.3.7 CreateNonEnumerableDataPropertyOrThrow (O,P,V )
The abstract operation CreateNonEnumerableDataPropertyOrThrow takes argumentsO (an Object),P (a
Assert :O is an ordinary, extensible object with no non-configurable properties.- LetnewDesc be the PropertyDescriptor {[[Value]]:V,[[Writable]]:
true ,[[Enumerable]]:false ,[[Configurable]]:true }. - Perform !
DefinePropertyOrThrow (O,P,newDesc). - Return
unused .
This abstract operation creates a property whose attributes are set to the same defaults used for properties created by the ECMAScript language assignment operator except it is not enumerable. Normally, the property will not already exist. If it does exist,
7.3.8 DefinePropertyOrThrow (O,P,desc )
The abstract operation DefinePropertyOrThrow takes argumentsO (an Object),P (a
- Letsuccess be ? O.[[DefineOwnProperty]](P,desc).
- Ifsuccess is
false , throw aTypeError exception. - Return
unused .
7.3.9 DeletePropertyOrThrow (O,P )
The abstract operation DeletePropertyOrThrow takes argumentsO (an Object) andP (a
- Letsuccess be ? O.[[Delete]](P).
- Ifsuccess is
false , throw aTypeError exception. - Return
unused .
7.3.10 GetMethod (V,P )
The abstract operation GetMethod takes argumentsV (an
- Letfunc be ?
GetV (V,P). - Iffunc is either
undefined ornull , returnundefined . - If
IsCallable (func) isfalse , throw aTypeError exception. - Returnfunc.
7.3.11 HasProperty (O,P )
The abstract operation HasProperty takes argumentsO (an Object) andP (a
- Return ? O.[[HasProperty]](P).
7.3.12 HasOwnProperty (O,P )
The abstract operation HasOwnProperty takes argumentsO (an Object) andP (a
- Letdesc be ? O.[[GetOwnProperty]](P).
- Ifdesc is
undefined , returnfalse . - Return
true .
7.3.13 Call (F,V [ ,argumentsList ] )
The abstract operation Call takes argumentsF (an
- IfargumentsList is not present, setargumentsList to a new empty
List . - If
IsCallable (F) isfalse , throw aTypeError exception. - Return ? F.[[Call]](V,argumentsList).
7.3.14 Construct (F [ ,argumentsList [ ,newTarget ] ] )
The abstract operation Construct takes argumentF (a
- IfnewTarget is not present, setnewTarget toF.
- IfargumentsList is not present, setargumentsList to a new empty
List . - Return ? F.[[Construct]](argumentsList,newTarget).
IfnewTarget is not present, this operation is equivalent to:new F(...argumentsList)
7.3.15 SetIntegrityLevel (O,level )
The abstract operation SetIntegrityLevel takes argumentsO (an Object) andlevel (
- Letstatus be ? O.[[PreventExtensions]]().
- Ifstatus is
false , returnfalse . - Letkeys be ? O.[[OwnPropertyKeys]]().
- Iflevel is
sealed , then- For each elementk ofkeys, do
- Perform ?
DefinePropertyOrThrow (O,k, PropertyDescriptor {[[Configurable]]:false }).
- Perform ?
- For each elementk ofkeys, do
- Else,
Assert :level isfrozen .- For each elementk ofkeys, do
- LetcurrentDesc be ? O.[[GetOwnProperty]](k).
- IfcurrentDesc is not
undefined , then- If
IsAccessorDescriptor (currentDesc) istrue , then- Letdesc be the PropertyDescriptor {[[Configurable]]:
false }.
- Letdesc be the PropertyDescriptor {[[Configurable]]:
- Else,
- Letdesc be the PropertyDescriptor {[[Configurable]]:
false ,[[Writable]]:false }.
- Letdesc be the PropertyDescriptor {[[Configurable]]:
- Perform ?
DefinePropertyOrThrow (O,k,desc).
- If
- Return
true .
7.3.16 TestIntegrityLevel (O,level )
The abstract operation TestIntegrityLevel takes argumentsO (an Object) andlevel (
- Letextensible be ?
IsExtensible (O). - Ifextensible is
true , returnfalse . - NOTE: If the object is extensible, none of its properties are examined.
- Letkeys be ? O.[[OwnPropertyKeys]]().
- For each elementk ofkeys, do
- LetcurrentDesc be ? O.[[GetOwnProperty]](k).
- IfcurrentDesc is not
undefined , then- IfcurrentDesc.[[Configurable]] is
true , returnfalse . - Iflevel is
frozen andIsDataDescriptor (currentDesc) istrue , then- IfcurrentDesc.[[Writable]] is
true , returnfalse .
- IfcurrentDesc.[[Writable]] is
- IfcurrentDesc.[[Configurable]] is
- Return
true .
7.3.17 CreateArrayFromList (elements )
The abstract operation CreateArrayFromList takes argumentelements (a
- Letarray be !
ArrayCreate (0). - Letn be 0.
- For each elemente ofelements, do
- Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (n)),e). - Setn ton + 1.
- Perform !
- Returnarray.
7.3.18 LengthOfArrayLike (obj )
The abstract operation LengthOfArrayLike takes argumentobj (an Object) and returns either a
Anarray-like object is any object for which this operation returns a
7.3.19 CreateListFromArrayLike (obj [ ,elementTypes ] )
The abstract operation CreateListFromArrayLike takes argumentobj (an
- IfelementTypes is not present, setelementTypes to « Undefined, Null, Boolean, String, Symbol, Number, BigInt, Object ».
- Ifobj
is not an Object , throw aTypeError exception. - Letlen be ?
LengthOfArrayLike (obj). - Letlist be a new empty
List . - Letindex be 0.
- Repeat, whileindex <len,
- Returnlist.
7.3.20 Invoke (V,P [ ,argumentsList ] )
The abstract operation Invoke takes argumentsV (an
7.3.21 OrdinaryHasInstance (C,O )
The abstract operation OrdinaryHasInstance takes argumentsC (an
- If
IsCallable (C) isfalse , returnfalse . - IfC has a[[BoundTargetFunction]] internal slot, then
- LetBC beC.[[BoundTargetFunction]].
- Return ?
InstanceofOperator (O,BC).
- IfO
is not an Object , returnfalse . - LetP be ?
Get (C,"prototype" ). - IfP
is not an Object , throw aTypeError exception. - Repeat,
- SetO to ? O.[[GetPrototypeOf]]().
- IfO is
null , returnfalse . - If
SameValue (P,O) istrue , returntrue .
7.3.22 SpeciesConstructor (O,defaultConstructor )
The abstract operation SpeciesConstructor takes argumentsO (an Object) anddefaultConstructor (a
- LetC be ?
Get (O,"constructor" ). - IfC is
undefined , returndefaultConstructor. - IfC
is not an Object , throw aTypeError exception. - LetS be ?
Get (C,@@species ). - IfS is either
undefined ornull , returndefaultConstructor. - If
IsConstructor (S) istrue , returnS. - Throw a
TypeError exception.
7.3.23 EnumerableOwnProperties (O,kind )
The abstract operation EnumerableOwnProperties takes argumentsO (an Object) andkind (
- LetownKeys be ? O.[[OwnPropertyKeys]]().
- Letresults be a new empty
List . - For each elementkey ofownKeys, do
- Ifkey
is a String , then- Letdesc be ? O.[[GetOwnProperty]](key).
- Ifdesc is not
undefined anddesc.[[Enumerable]] istrue , then- Ifkind is
key , then- Appendkey toresults.
- Else,
- Letvalue be ?
Get (O,key). - Ifkind is
value , then- Appendvalue toresults.
- Else,
Assert :kind iskey+value .- Letentry be
CreateArrayFromList («key,value »). - Appendentry toresults.
- Letvalue be ?
- Ifkind is
- Ifkey
- Returnresults.
7.3.24 GetFunctionRealm (obj )
The abstract operation GetFunctionRealm takes argumentobj (a
- Ifobj has a[[Realm]] internal slot, then
- Returnobj.[[Realm]].
- Ifobj is a
bound function exotic object , then- LetboundTargetFunction beobj.[[BoundTargetFunction]].
- Return ?
GetFunctionRealm (boundTargetFunction).
- Ifobj is a
Proxy exotic object , then- Perform ?
ValidateNonRevokedProxy (obj). - LetproxyTarget beobj.[[ProxyTarget]].
- Return ?
GetFunctionRealm (proxyTarget).
- Perform ?
- Return
the current Realm Record .
Step
7.3.25 CopyDataProperties (target,source,excludedItems )
The abstract operation CopyDataProperties takes argumentstarget (an Object),source (an
- Ifsource is either
undefined ornull , returnunused . - Letfrom be !
ToObject (source). - Letkeys be ? from.[[OwnPropertyKeys]]().
- For each elementnextKey ofkeys, do
- Letexcluded be
false . - For each elemente ofexcludedItems, do
- If
SameValue (e,nextKey) istrue , then- Setexcluded to
true .
- Setexcluded to
- If
- Ifexcluded is
false , then- Letdesc be ? from.[[GetOwnProperty]](nextKey).
- Ifdesc is not
undefined anddesc.[[Enumerable]] istrue , then- LetpropValue be ?
Get (from,nextKey). - Perform !
CreateDataPropertyOrThrow (target,nextKey,propValue).
- LetpropValue be ?
- Letexcluded be
- Return
unused .
The target passed in here is always a newly created object which is not directly accessible in case of an error being thrown.
7.3.26 PrivateElementFind (O,P )
The abstract operation PrivateElementFind takes argumentsO (an Object) andP (a
- IfO.[[PrivateElements]] contains a
PrivateElement pe such thatpe.[[Key]] isP, then- Returnpe.
- Return
empty .
7.3.27 PrivateFieldAdd (O,P,value )
The abstract operation PrivateFieldAdd takes argumentsO (an Object),P (a
- If the
host is a web browser, then- Perform ?
HostEnsureCanAddPrivateElement (O).
- Perform ?
- Letentry be
PrivateElementFind (O,P). - Ifentry is not
empty , throw aTypeError exception. - Append
PrivateElement {[[Key]]:P,[[Kind]]:field ,[[Value]]:value } toO.[[PrivateElements]]. - Return
unused .
7.3.28 PrivateMethodOrAccessorAdd (O,method )
The abstract operation PrivateMethodOrAccessorAdd takes argumentsO (an Object) andmethod (a
Assert :method.[[Kind]] is eithermethod oraccessor .- If the
host is a web browser, then- Perform ?
HostEnsureCanAddPrivateElement (O).
- Perform ?
- Letentry be
PrivateElementFind (O,method.[[Key]]). - Ifentry is not
empty , throw aTypeError exception. - Appendmethod toO.[[PrivateElements]].
- Return
unused .
The values for private methods and accessors are shared across instances. This operation does not create a new copy of the method or accessor.
7.3.29 HostEnsureCanAddPrivateElement (O )
The
An implementation of HostEnsureCanAddPrivateElement must conform to the following requirements:
- IfO is not a
host-defined exotic object , this abstract operation must returnNormalCompletion (unused ) and perform no other steps. - Any two calls of this abstract operation with the same argument must return the same kind of
Completion Record .
The default implementation of HostEnsureCanAddPrivateElement is to return
This abstract operation is only invoked by ECMAScript
7.3.30 PrivateGet (O,P )
The abstract operation PrivateGet takes argumentsO (an Object) andP (a
- Letentry be
PrivateElementFind (O,P). - Ifentry is
empty , throw aTypeError exception. - Ifentry.[[Kind]] is either
field ormethod , then- Returnentry.[[Value]].
Assert :entry.[[Kind]] isaccessor .- Ifentry.[[Get]] is
undefined , throw aTypeError exception. - Letgetter beentry.[[Get]].
- Return ?
Call (getter,O).
7.3.31 PrivateSet (O,P,value )
The abstract operation PrivateSet takes argumentsO (an Object),P (a
- Letentry be
PrivateElementFind (O,P). - Ifentry is
empty , throw aTypeError exception. - Ifentry.[[Kind]] is
field , then- Setentry.[[Value]] tovalue.
- Else ifentry.[[Kind]] is
method , then- Throw a
TypeError exception.
- Throw a
- Else,
- Return
unused .
7.3.32 DefineField (receiver,fieldRecord )
The abstract operation DefineField takes argumentsreceiver (an Object) andfieldRecord (a
- LetfieldName befieldRecord.[[Name]].
- Letinitializer befieldRecord.[[Initializer]].
- Ifinitializer is not
empty , then- LetinitValue be ?
Call (initializer,receiver).
- LetinitValue be ?
- Else,
- LetinitValue be
undefined .
- LetinitValue be
- IffieldName is a
Private Name , then- Perform ?
PrivateFieldAdd (receiver,fieldName,initValue).
- Perform ?
- Else,
Assert :IsPropertyKey (fieldName) istrue .- Perform ?
CreateDataPropertyOrThrow (receiver,fieldName,initValue).
- Return
unused .
7.3.33 InitializeInstanceElements (O,constructor )
The abstract operation InitializeInstanceElements takes argumentsO (an Object) andconstructor (an ECMAScript
- Letmethods be the value ofconstructor.[[PrivateMethods]].
- For each
PrivateElement method ofmethods, do- Perform ?
PrivateMethodOrAccessorAdd (O,method).
- Perform ?
- Letfields be the value ofconstructor.[[Fields]].
- For each elementfieldRecord offields, do
- Perform ?
DefineField (O,fieldRecord).
- Perform ?
- Return
unused .
7.3.34 AddValueToKeyedGroup (groups,key,value )
The abstract operation AddValueToKeyedGroup takes argumentsgroups (a
7.3.35 GroupBy (items,callbackfn,keyCoercion )
The abstract operation GroupBy takes argumentsitems (an
- Perform ?
RequireObjectCoercible (items). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letgroups be a new empty
List . - LetiteratorRecord be ?
GetIterator (items,sync ). - Letk be 0.
- Repeat,
- Ifk ≥ 253 - 1, then
- Leterror be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord,error).
- Leterror be
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- Returngroups.
- Letvalue benext.
- Letkey be
Completion (Call (callbackfn,undefined , «value,𝔽 (k) »)). IfAbruptCloseIterator (key,iteratorRecord).- IfkeyCoercion is
property , then- Setkey to
Completion (ToPropertyKey (key)). IfAbruptCloseIterator (key,iteratorRecord).
- Setkey to
- Else,
Assert :keyCoercion iszero .- Ifkey is
-0 𝔽, setkey to+0 𝔽.
- Perform
AddValueToKeyedGroup (groups,key,value). - Setk tok + 1.
- Ifk ≥ 253 - 1, then
7.4 Operations on Iterator Objects
See Common Iteration Interfaces (
7.4.1 Iterator Records
AnIterator Record is anext method.
Iterator Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Iterator]] | an Object | An object that conforms to theIterator orAsyncIterator interface. |
| [[NextMethod]] | an | Thenext method of the[[Iterator]] object. |
| [[Done]] | a Boolean | Whether the iterator has been closed. |
7.4.2 GetIteratorFromMethod (obj,method )
The abstract operation GetIteratorFromMethod takes argumentsobj (an
- Letiterator be ?
Call (method,obj). - Ifiterator
is not an Object , throw aTypeError exception. - LetnextMethod be ?
Get (iterator,"next" ). - LetiteratorRecord be the
Iterator Record {[[Iterator]]:iterator,[[NextMethod]]:nextMethod,[[Done]]:false }. - ReturniteratorRecord.
7.4.3 GetIterator (obj,kind )
The abstract operation GetIterator takes argumentsobj (an
- Ifkind is
async , then- Letmethod be ?
GetMethod (obj,@@asyncIterator ). - Ifmethod is
undefined , then- LetsyncMethod be ?
GetMethod (obj,@@iterator ). - IfsyncMethod is
undefined , throw aTypeError exception. - LetsyncIteratorRecord be ?
GetIteratorFromMethod (obj,syncMethod). - Return
CreateAsyncFromSyncIterator (syncIteratorRecord).
- LetsyncMethod be ?
- Letmethod be ?
- Else,
- Letmethod be ?
GetMethod (obj,@@iterator ).
- Letmethod be ?
- Ifmethod is
undefined , throw aTypeError exception. - Return ?
GetIteratorFromMethod (obj,method).
7.4.4 IteratorNext (iteratorRecord [ ,value ] )
The abstract operation IteratorNext takes argumentiteratorRecord (an
- Ifvalue is not present, then
- Letresult be ?
Call (iteratorRecord.[[NextMethod]],iteratorRecord.[[Iterator]]).
- Letresult be ?
- Else,
- Letresult be ?
Call (iteratorRecord.[[NextMethod]],iteratorRecord.[[Iterator]], «value »).
- Letresult be ?
- Ifresult
is not an Object , throw aTypeError exception. - Returnresult.
7.4.5 IteratorComplete (iterResult )
The abstract operation IteratorComplete takes argumentiterResult (an Object) and returns either a
7.4.6 IteratorValue (iterResult )
The abstract operation IteratorValue takes argumentiterResult (an Object) and returns either a
- Return ?
Get (iterResult,"value" ).
7.4.7 IteratorStep (iteratorRecord )
The abstract operation IteratorStep takes argumentiteratorRecord (an
- Letresult be ?
IteratorNext (iteratorRecord). - Letdone be ?
IteratorComplete (result). - Ifdone is
true , returnfalse . - Returnresult.
7.4.8 IteratorStepValue (iteratorRecord )
The abstract operation IteratorStepValue takes argumentiteratorRecord (an
- Letresult be
Completion (IteratorNext (iteratorRecord)). - Ifresult is a
throw completion , then- SetiteratorRecord.[[Done]] to
true . - Return ? result.
- SetiteratorRecord.[[Done]] to
- Setresult to ! result.
- Letdone be
Completion (IteratorComplete (result)). - Ifdone is a
throw completion , then- SetiteratorRecord.[[Done]] to
true . - Return ? done.
- SetiteratorRecord.[[Done]] to
- Setdone to ! done.
- Ifdone is
true , then- SetiteratorRecord.[[Done]] to
true . - Return
done .
- SetiteratorRecord.[[Done]] to
- Letvalue be
Completion (Get (result,"value" )). - Ifvalue is a
throw completion , then- SetiteratorRecord.[[Done]] to
true .
- SetiteratorRecord.[[Done]] to
- Return ? value.
7.4.9 IteratorClose (iteratorRecord,completion )
The abstract operation IteratorClose takes argumentsiteratorRecord (an
Assert :iteratorRecord.[[Iterator]]is an Object .- Letiterator beiteratorRecord.[[Iterator]].
- LetinnerResult be
Completion (GetMethod (iterator,"return" )). - IfinnerResult is a
normal completion , then- Letreturn beinnerResult.[[Value]].
- Ifreturn is
undefined , return ? completion. - SetinnerResult to
Completion (Call (return,iterator)).
- Ifcompletion is a
throw completion , return ? completion. - IfinnerResult is a
throw completion , return ? innerResult. - IfinnerResult.[[Value]]
is not an Object , throw aTypeError exception. - Return ? completion.
7.4.10 IfAbruptCloseIterator (value,iteratorRecord )
IfAbruptCloseIterator is a shorthand for a sequence of algorithm steps that use an
IfAbruptCloseIterator (value,iteratorRecord).
means the same thing as:
Assert :value is aCompletion Record .- Ifvalue is an
abrupt completion , return ?IteratorClose (iteratorRecord,value). - Else, setvalue to ! value.
7.4.11 AsyncIteratorClose (iteratorRecord,completion )
The abstract operation AsyncIteratorClose takes argumentsiteratorRecord (an
Assert :iteratorRecord.[[Iterator]]is an Object .- Letiterator beiteratorRecord.[[Iterator]].
- LetinnerResult be
Completion (GetMethod (iterator,"return" )). - IfinnerResult is a
normal completion , then- Letreturn beinnerResult.[[Value]].
- Ifreturn is
undefined , return ? completion. - SetinnerResult to
Completion (Call (return,iterator)). - IfinnerResult is a
normal completion , setinnerResult toCompletion (Await (innerResult.[[Value]])).
- Ifcompletion is a
throw completion , return ? completion. - IfinnerResult is a
throw completion , return ? innerResult. - IfinnerResult.[[Value]]
is not an Object , throw aTypeError exception. - Return ? completion.
7.4.12 CreateIterResultObject (value,done )
The abstract operation CreateIterResultObject takes argumentsvalue (an
- Letobj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"value" ,value). - Perform !
CreateDataPropertyOrThrow (obj,"done" ,done). - Returnobj.
7.4.13 CreateListIteratorRecord (list )
The abstract operation CreateListIteratorRecord takes argumentlist (anext method returns the successive elements oflist. It performs the following steps when called:
- Letclosure be a new
Abstract Closure with no parameters that captureslist and performs the following steps when called:- For each elementE oflist, do
- Perform ?
GeneratorYield (CreateIterResultObject (E,false )).
- Perform ?
- Return
NormalCompletion (undefined ).
- For each elementE oflist, do
- Letiterator be
CreateIteratorFromClosure (closure,empty ,%IteratorPrototype% ). - Return the
Iterator Record {[[Iterator]]:iterator,[[NextMethod]]: %GeneratorFunction.prototype.prototype.next%,[[Done]]:false }.
The list iterator object is never directly accessible to ECMAScript code.
7.4.14 IteratorToList (iteratorRecord )
The abstract operation IteratorToList takes argumentiteratorRecord (an
- Letvalues be a new empty
List . - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- Returnvalues.
- Appendnext tovalues.
- Letnext be ?
8 Syntax-Directed Operations
In addition to those defined in this section, specialized
8.1 Runtime Semantics: Evaluation
The
8.2 Scope Analysis
8.2.1 Static Semantics: BoundNames
The
It is defined piecewise over the following productions:
- Return a
List whose sole element is theStringValue ofIdentifier .
- Return «
"yield" ».
- Return «
"await" ».
- Return the
BoundNames ofBindingList .
- Letnames1 be the
BoundNames ofBindingList . - Letnames2 be the
BoundNames ofLexicalBinding . - Return the
list-concatenation ofnames1 andnames2.
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Letnames1 be
BoundNames ofVariableDeclarationList . - Letnames2 be
BoundNames ofVariableDeclaration . - Return the
list-concatenation ofnames1 andnames2.
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Return a new empty
List .
- Letnames1 be
BoundNames ofBindingPropertyList . - Letnames2 be
BoundNames ofBindingRestProperty . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- Return the
BoundNames ofBindingRestElement .
- Return the
BoundNames ofBindingElementList .
- Letnames1 be
BoundNames ofBindingElementList . - Letnames2 be
BoundNames ofBindingRestElement . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be
BoundNames ofBindingPropertyList . - Letnames2 be
BoundNames ofBindingProperty . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be
BoundNames ofBindingElementList . - Letnames2 be
BoundNames ofBindingElisionElement . - Return the
list-concatenation ofnames1 andnames2.
- Return
BoundNames ofBindingElement .
- Return the
BoundNames ofBindingElement .
- Return the
BoundNames ofBindingIdentifier .
- Return the
BoundNames ofBindingPattern .
- Return the
BoundNames ofForBinding .
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return a new empty
List .
- Letnames1 be
BoundNames ofFormalParameterList . - Letnames2 be
BoundNames ofFunctionRestParameter . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be
BoundNames ofFormalParameterList . - Letnames2 be
BoundNames ofFormalParameter . - Return the
list-concatenation ofnames1 andnames2.
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return the
BoundNames offormals.
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Return the
BoundNames ofBindingIdentifier .
- Return «
"*default*" ».
- Lethead be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Return the
BoundNames ofhead.
- Return the
BoundNames ofImportClause .
- Return a new empty
List .
- Letnames1 be the
BoundNames ofImportedDefaultBinding . - Letnames2 be the
BoundNames ofNameSpaceImport . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be the
BoundNames ofImportedDefaultBinding . - Letnames2 be the
BoundNames ofNamedImports . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- Letnames1 be the
BoundNames ofImportsList . - Letnames2 be the
BoundNames ofImportSpecifier . - Return the
list-concatenation ofnames1 andnames2.
- Return the
BoundNames ofImportedBinding .
- Return a new empty
List .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- LetdeclarationNames be the
BoundNames ofHoistableDeclaration . - IfdeclarationNames does not include the element
"*default*" , append"*default*" todeclarationNames. - ReturndeclarationNames.
- LetdeclarationNames be the
BoundNames ofClassDeclaration . - IfdeclarationNames does not include the element
"*default*" , append"*default*" todeclarationNames. - ReturndeclarationNames.
- Return «
"*default*" ».
8.2.2 Static Semantics: DeclarationPart
The
- Return
FunctionDeclaration .
- Return
GeneratorDeclaration .
- Return
AsyncFunctionDeclaration .
- Return
AsyncGeneratorDeclaration .
- Return
ClassDeclaration .
- Return
LexicalDeclaration .
8.2.3 Static Semantics: IsConstantDeclaration
The
- Return
IsConstantDeclaration ofLetOrConst .
- Return
false .
- Return
true .
- Return
false .
- Return
false .
- Return
false .
It is not necessary to treatexport default
8.2.4 Static Semantics: LexicallyDeclaredNames
The
- Return a new empty
List .
- Letnames1 be
LexicallyDeclaredNames ofStatementList . - Letnames2 be
LexicallyDeclaredNames ofStatementListItem . - Return the
list-concatenation ofnames1 andnames2.
- If
Statement isStatement : LabelledStatement LexicallyDeclaredNames ofLabelledStatement . - Return a new empty
List .
- Return the
BoundNames ofDeclaration .
- Return a new empty
List .
- If the first
CaseClauses is present, letnames1 be theLexicallyDeclaredNames of the firstCaseClauses . - Else, letnames1 be a new empty
List . - Letnames2 be
LexicallyDeclaredNames ofDefaultClause . - If the second
CaseClauses is present, letnames3 be theLexicallyDeclaredNames of the secondCaseClauses . - Else, letnames3 be a new empty
List . - Return the
list-concatenation ofnames1,names2, andnames3.
- Letnames1 be
LexicallyDeclaredNames ofCaseClauses . - Letnames2 be
LexicallyDeclaredNames ofCaseClause . - Return the
list-concatenation ofnames1 andnames2.
- If the
StatementList is present, return theLexicallyDeclaredNames ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theLexicallyDeclaredNames ofStatementList . - Return a new empty
List .
- Return the
LexicallyDeclaredNames ofLabelledItem .
- Return a new empty
List .
- Return
BoundNames ofFunctionDeclaration .
- Return a new empty
List .
- Return a new empty
List .
- Return the
TopLevelLexicallyDeclaredNames ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
At the top level of a
The LexicallyDeclaredNames of a
- Letnames1 be
LexicallyDeclaredNames ofModuleItemList . - Letnames2 be
LexicallyDeclaredNames ofModuleItem . - Return the
list-concatenation ofnames1 andnames2.
- Return the
BoundNames ofImportDeclaration .
- If
ExportDeclaration isexportVariableStatement , return a new emptyList . - Return the
BoundNames ofExportDeclaration .
- Return
LexicallyDeclaredNames ofStatementListItem .
At the top level of a
8.2.5 Static Semantics: LexicallyScopedDeclarations
The
- Letdeclarations1 be
LexicallyScopedDeclarations ofStatementList . - Letdeclarations2 be
LexicallyScopedDeclarations ofStatementListItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- If
Statement isStatement : LabelledStatement LexicallyScopedDeclarations ofLabelledStatement . - Return a new empty
List .
- Return a
List whose sole element isDeclarationPart ofDeclaration .
- Return a new empty
List .
- If the first
CaseClauses is present, letdeclarations1 be theLexicallyScopedDeclarations of the firstCaseClauses . - Else, letdeclarations1 be a new empty
List . - Letdeclarations2 be
LexicallyScopedDeclarations ofDefaultClause . - If the second
CaseClauses is present, letdeclarations3 be theLexicallyScopedDeclarations of the secondCaseClauses . - Else, letdeclarations3 be a new empty
List . - Return the
list-concatenation ofdeclarations1,declarations2, anddeclarations3.
- Letdeclarations1 be
LexicallyScopedDeclarations ofCaseClauses . - Letdeclarations2 be
LexicallyScopedDeclarations ofCaseClause . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- If the
StatementList is present, return theLexicallyScopedDeclarations ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theLexicallyScopedDeclarations ofStatementList . - Return a new empty
List .
- Return the
LexicallyScopedDeclarations ofLabelledItem .
- Return a new empty
List .
- Return «
FunctionDeclaration ».
- Return a new empty
List .
- Return the
TopLevelLexicallyScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return the
TopLevelLexicallyScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Letdeclarations1 be
LexicallyScopedDeclarations ofModuleItemList . - Letdeclarations2 be
LexicallyScopedDeclarations ofModuleItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return a new empty
List .
- Return a new empty
List .
- Return a
List whose sole element isDeclarationPart ofDeclaration .
- Return a
List whose sole element isDeclarationPart ofHoistableDeclaration .
- Return a
List whose sole element isClassDeclaration .
- Return a
List whose sole element is thisExportDeclaration .
8.2.6 Static Semantics: VarDeclaredNames
The
- Return a new empty
List .
- Return a new empty
List .
- Letnames1 be
VarDeclaredNames ofStatementList . - Letnames2 be
VarDeclaredNames ofStatementListItem . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- Return
BoundNames ofVariableDeclarationList .
- Letnames1 be
VarDeclaredNames of the firstStatement . - Letnames2 be
VarDeclaredNames of the secondStatement . - Return the
list-concatenation ofnames1 andnames2.
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Letnames1 be
BoundNames ofVariableDeclarationList . - Letnames2 be
VarDeclaredNames ofStatement . - Return the
list-concatenation ofnames1 andnames2.
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofStatement .
- Letnames1 be the
BoundNames ofForBinding . - Letnames2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation ofnames1 andnames2.
This section is extended by Annex
- Return the
VarDeclaredNames ofStatement .
- Return the
VarDeclaredNames ofCaseBlock .
- Return a new empty
List .
- If the first
CaseClauses is present, letnames1 be theVarDeclaredNames of the firstCaseClauses . - Else, letnames1 be a new empty
List . - Letnames2 be
VarDeclaredNames ofDefaultClause . - If the second
CaseClauses is present, letnames3 be theVarDeclaredNames of the secondCaseClauses . - Else, letnames3 be a new empty
List . - Return the
list-concatenation ofnames1,names2, andnames3.
- Letnames1 be
VarDeclaredNames ofCaseClauses . - Letnames2 be
VarDeclaredNames ofCaseClause . - Return the
list-concatenation ofnames1 andnames2.
- If the
StatementList is present, return theVarDeclaredNames ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theVarDeclaredNames ofStatementList . - Return a new empty
List .
- Return the
VarDeclaredNames ofLabelledItem .
- Return a new empty
List .
- Letnames1 be
VarDeclaredNames ofBlock . - Letnames2 be
VarDeclaredNames ofCatch . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be
VarDeclaredNames ofBlock . - Letnames2 be
VarDeclaredNames ofFinally . - Return the
list-concatenation ofnames1 andnames2.
- Letnames1 be
VarDeclaredNames ofBlock . - Letnames2 be
VarDeclaredNames ofCatch . - Letnames3 be
VarDeclaredNames ofFinally . - Return the
list-concatenation ofnames1,names2, andnames3.
- Return the
VarDeclaredNames ofBlock .
- Return a new empty
List .
- Return
TopLevelVarDeclaredNames ofStatementList .
- Return a new empty
List .
- Return the
TopLevelVarDeclaredNames ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return
TopLevelVarDeclaredNames ofStatementList .
- Letnames1 be
VarDeclaredNames ofModuleItemList . - Letnames2 be
VarDeclaredNames ofModuleItem . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- If
ExportDeclaration isexportVariableStatement , returnBoundNames ofExportDeclaration . - Return a new empty
List .
8.2.7 Static Semantics: VarScopedDeclarations
The
- Return a new empty
List .
- Return a new empty
List .
- Letdeclarations1 be
VarScopedDeclarations ofStatementList . - Letdeclarations2 be
VarScopedDeclarations ofStatementListItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return a new empty
List .
- Return «
VariableDeclaration ».
- Letdeclarations1 be
VarScopedDeclarations ofVariableDeclarationList . - Return the
list-concatenation ofdeclarations1 and «VariableDeclaration ».
- Letdeclarations1 be
VarScopedDeclarations of the firstStatement . - Letdeclarations2 be
VarScopedDeclarations of the secondStatement . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Letdeclarations1 be
VarScopedDeclarations ofVariableDeclarationList . - Letdeclarations2 be
VarScopedDeclarations ofStatement . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofStatement .
- Letdeclarations1 be «
ForBinding ». - Letdeclarations2 be
VarScopedDeclarations ofStatement . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
This section is extended by Annex
- Return the
VarScopedDeclarations ofStatement .
- Return the
VarScopedDeclarations ofCaseBlock .
- Return a new empty
List .
- If the first
CaseClauses is present, letdeclarations1 be theVarScopedDeclarations of the firstCaseClauses . - Else, letdeclarations1 be a new empty
List . - Letdeclarations2 be
VarScopedDeclarations ofDefaultClause . - If the second
CaseClauses is present, letdeclarations3 be theVarScopedDeclarations of the secondCaseClauses . - Else, letdeclarations3 be a new empty
List . - Return the
list-concatenation ofdeclarations1,declarations2, anddeclarations3.
- Letdeclarations1 be
VarScopedDeclarations ofCaseClauses . - Letdeclarations2 be
VarScopedDeclarations ofCaseClause . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- If the
StatementList is present, return theVarScopedDeclarations ofStatementList . - Return a new empty
List .
- If the
StatementList is present, return theVarScopedDeclarations ofStatementList . - Return a new empty
List .
- Return the
VarScopedDeclarations ofLabelledItem .
- Return a new empty
List .
- Letdeclarations1 be
VarScopedDeclarations ofBlock . - Letdeclarations2 be
VarScopedDeclarations ofCatch . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Letdeclarations1 be
VarScopedDeclarations ofBlock . - Letdeclarations2 be
VarScopedDeclarations ofFinally . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Letdeclarations1 be
VarScopedDeclarations ofBlock . - Letdeclarations2 be
VarScopedDeclarations ofCatch . - Letdeclarations3 be
VarScopedDeclarations ofFinally . - Return the
list-concatenation ofdeclarations1,declarations2, anddeclarations3.
- Return the
VarScopedDeclarations ofBlock .
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofStatementList .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Return a new empty
List .
- Letdeclarations1 be
VarScopedDeclarations ofModuleItemList . - Letdeclarations2 be
VarScopedDeclarations ofModuleItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return a new empty
List .
- If
ExportDeclaration isexportVariableStatement , returnVarScopedDeclarations ofVariableStatement . - Return a new empty
List .
8.2.8 Static Semantics: TopLevelLexicallyDeclaredNames
The
- Letnames1 be
TopLevelLexicallyDeclaredNames ofStatementList . - Letnames2 be
TopLevelLexicallyDeclaredNames ofStatementListItem . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- If
Declaration isDeclaration : HoistableDeclaration - Return a new empty
List .
- Return a new empty
- Return the
BoundNames ofDeclaration .
At the top level of a function, or script, function declarations are treated like var declarations rather than like lexical declarations.
8.2.9 Static Semantics: TopLevelLexicallyScopedDeclarations
The
- Letdeclarations1 be
TopLevelLexicallyScopedDeclarations ofStatementList . - Letdeclarations2 be
TopLevelLexicallyScopedDeclarations ofStatementListItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- Return a new empty
List .
- If
Declaration isDeclaration : HoistableDeclaration - Return a new empty
List .
- Return a new empty
- Return «
Declaration ».
8.2.10 Static Semantics: TopLevelVarDeclaredNames
The
- Letnames1 be
TopLevelVarDeclaredNames ofStatementList . - Letnames2 be
TopLevelVarDeclaredNames ofStatementListItem . - Return the
list-concatenation ofnames1 andnames2.
- If
Declaration isDeclaration : HoistableDeclaration - Return the
BoundNames ofHoistableDeclaration .
- Return the
- Return a new empty
List .
- If
Statement isStatement : LabelledStatement TopLevelVarDeclaredNames ofStatement . - Return
VarDeclaredNames ofStatement .
At the top level of a function or script, inner function declarations are treated like var declarations.
- Return the
TopLevelVarDeclaredNames ofLabelledItem .
- If
Statement isStatement : LabelledStatement TopLevelVarDeclaredNames ofStatement . - Return
VarDeclaredNames ofStatement .
- Return
BoundNames ofFunctionDeclaration .
8.2.11 Static Semantics: TopLevelVarScopedDeclarations
The
- Letdeclarations1 be
TopLevelVarScopedDeclarations ofStatementList . - Letdeclarations2 be
TopLevelVarScopedDeclarations ofStatementListItem . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
- If
Statement isStatement : LabelledStatement TopLevelVarScopedDeclarations ofStatement . - Return
VarScopedDeclarations ofStatement .
- If
Declaration isDeclaration : HoistableDeclaration - Letdeclaration be
DeclarationPart ofHoistableDeclaration . - Return «declaration ».
- Letdeclaration be
- Return a new empty
List .
- Return the
TopLevelVarScopedDeclarations ofLabelledItem .
- If
Statement isStatement : LabelledStatement TopLevelVarScopedDeclarations ofStatement . - Return
VarScopedDeclarations ofStatement .
- Return «
FunctionDeclaration ».
8.3 Labels
8.3.1 Static Semantics: ContainsDuplicateLabels
The
- Return
false .
- LethasDuplicates be
ContainsDuplicateLabels ofStatementList with argumentlabelSet. - IfhasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofStatementListItem with argumentlabelSet.
- LethasDuplicate be
ContainsDuplicateLabels of the firstStatement with argumentlabelSet. - IfhasDuplicate is
true , returntrue . - Return
ContainsDuplicateLabels of the secondStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
This section is extended by Annex
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
- Return
ContainsDuplicateLabels ofCaseBlock with argumentlabelSet.
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsDuplicateLabels of the firstCaseClauses with argumentlabelSet istrue , returntrue .
- If
- If
ContainsDuplicateLabels ofDefaultClause with argumentlabelSet istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsDuplicateLabels of the secondCaseClauses with argumentlabelSet.
- LethasDuplicates be
ContainsDuplicateLabels ofCaseClauses with argumentlabelSet. - IfhasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofCaseClause with argumentlabelSet.
- If the
StatementList is present, returnContainsDuplicateLabels ofStatementList with argumentlabelSet. - Return
false .
- If the
StatementList is present, returnContainsDuplicateLabels ofStatementList with argumentlabelSet. - Return
false .
- Letlabel be the
StringValue ofLabelIdentifier . - IflabelSet containslabel, return
true . - LetnewLabelSet be the
list-concatenation oflabelSet and «label ». - Return
ContainsDuplicateLabels ofLabelledItem with argumentnewLabelSet.
- Return
false .
- LethasDuplicates be
ContainsDuplicateLabels ofBlock with argumentlabelSet. - IfhasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofCatch with argumentlabelSet.
- LethasDuplicates be
ContainsDuplicateLabels ofBlock with argumentlabelSet. - IfhasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofFinally with argumentlabelSet.
- If
ContainsDuplicateLabels ofBlock with argumentlabelSet istrue , returntrue . - If
ContainsDuplicateLabels ofCatch with argumentlabelSet istrue , returntrue . - Return
ContainsDuplicateLabels ofFinally with argumentlabelSet.
- Return
ContainsDuplicateLabels ofBlock with argumentlabelSet.
- Return
false .
- Return
false .
- LethasDuplicates be
ContainsDuplicateLabels ofModuleItemList with argumentlabelSet. - IfhasDuplicates is
true , returntrue . - Return
ContainsDuplicateLabels ofModuleItem with argumentlabelSet.
- Return
false .
8.3.2 Static Semantics: ContainsUndefinedBreakTarget
The
- Return
false .
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget ofStatementList with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofStatementListItem with argumentlabelSet.
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget of the firstStatement with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget of the secondStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
This section is extended by Annex
- Return
false .
- IflabelSet does not contain the
StringValue ofLabelIdentifier , returntrue . - Return
false .
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofCaseBlock with argumentlabelSet.
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsUndefinedBreakTarget of the firstCaseClauses with argumentlabelSet istrue , returntrue .
- If
- If
ContainsUndefinedBreakTarget ofDefaultClause with argumentlabelSet istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsUndefinedBreakTarget of the secondCaseClauses with argumentlabelSet.
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget ofCaseClauses with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofCaseClause with argumentlabelSet.
- If the
StatementList is present, returnContainsUndefinedBreakTarget ofStatementList with argumentlabelSet. - Return
false .
- If the
StatementList is present, returnContainsUndefinedBreakTarget ofStatementList with argumentlabelSet. - Return
false .
- Letlabel be the
StringValue ofLabelIdentifier . - LetnewLabelSet be the
list-concatenation oflabelSet and «label ». - Return
ContainsUndefinedBreakTarget ofLabelledItem with argumentnewLabelSet.
- Return
false .
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget ofBlock with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofCatch with argumentlabelSet.
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget ofBlock with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofFinally with argumentlabelSet.
- If
ContainsUndefinedBreakTarget ofBlock with argumentlabelSet istrue , returntrue . - If
ContainsUndefinedBreakTarget ofCatch with argumentlabelSet istrue , returntrue . - Return
ContainsUndefinedBreakTarget ofFinally with argumentlabelSet.
- Return
ContainsUndefinedBreakTarget ofBlock with argumentlabelSet.
- Return
false .
- Return
false .
- LethasUndefinedLabels be
ContainsUndefinedBreakTarget ofModuleItemList with argumentlabelSet. - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedBreakTarget ofModuleItem with argumentlabelSet.
- Return
false .
8.3.3 Static Semantics: ContainsUndefinedContinueTarget
The
- Return
false .
- Return
ContainsUndefinedContinueTarget ofBlockStatement with argumentsiterationSet and « ».
- LetnewIterationSet be the
list-concatenation ofiterationSet andlabelSet. - Return
ContainsUndefinedContinueTarget ofIterationStatement with argumentsnewIterationSet and « ».
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget ofStatementList with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofStatementListItem with argumentsiterationSet and « ».
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget of the firstStatement with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget of the secondStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
This section is extended by Annex
- Return
false .
- IfiterationSet does not contain the
StringValue ofLabelIdentifier , returntrue . - Return
false .
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofCaseBlock with argumentsiterationSet and « ».
- Return
false .
- If the first
CaseClauses is present, then- If
ContainsUndefinedContinueTarget of the firstCaseClauses with argumentsiterationSet and « » istrue , returntrue .
- If
- If
ContainsUndefinedContinueTarget ofDefaultClause with argumentsiterationSet and « » istrue , returntrue . - If the second
CaseClauses is not present, returnfalse . - Return
ContainsUndefinedContinueTarget of the secondCaseClauses with argumentsiterationSet and « ».
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget ofCaseClauses with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofCaseClause with argumentsiterationSet and « ».
- If the
StatementList is present, returnContainsUndefinedContinueTarget ofStatementList with argumentsiterationSet and « ». - Return
false .
- If the
StatementList is present, returnContainsUndefinedContinueTarget ofStatementList with argumentsiterationSet and « ». - Return
false .
- Letlabel be the
StringValue ofLabelIdentifier . - LetnewLabelSet be the
list-concatenation oflabelSet and «label ». - Return
ContainsUndefinedContinueTarget ofLabelledItem with argumentsiterationSet andnewLabelSet.
- Return
false .
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget ofBlock with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofCatch with argumentsiterationSet and « ».
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget ofBlock with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofFinally with argumentsiterationSet and « ».
- If
ContainsUndefinedContinueTarget ofBlock with argumentsiterationSet and « » istrue , returntrue . - If
ContainsUndefinedContinueTarget ofCatch with argumentsiterationSet and « » istrue , returntrue . - Return
ContainsUndefinedContinueTarget ofFinally with argumentsiterationSet and « ».
- Return
ContainsUndefinedContinueTarget ofBlock with argumentsiterationSet and « ».
- Return
false .
- Return
false .
- LethasUndefinedLabels be
ContainsUndefinedContinueTarget ofModuleItemList with argumentsiterationSet and « ». - IfhasUndefinedLabels is
true , returntrue . - Return
ContainsUndefinedContinueTarget ofModuleItem with argumentsiterationSet and « ».
- Return
false .
8.4 Function Name Inference
8.4.1 Static Semantics: HasName
The
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - If
IsFunctionDefinition ofexpr isfalse , returnfalse . - Return
HasName ofexpr.
- Return
false .
- Return
true .
8.4.2 Static Semantics: IsFunctionDefinition
The
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
IsFunctionDefinition ofexpr.
- Return
false .
- Return
true .
8.4.3 Static Semantics: IsAnonymousFunctionDefinition (expr )
The abstract operation IsAnonymousFunctionDefinition takes argumentexpr (an
- If
IsFunctionDefinition ofexpr isfalse , returnfalse . - LethasName be
HasName ofexpr. - IfhasName is
true , returnfalse . - Return
true .
8.4.4 Static Semantics: IsIdentifierRef
The
- Return
true .
- Return
false .
8.4.5 Runtime Semantics: NamedEvaluation
The
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
NamedEvaluation ofexpr with argumentname.
Assert :IsAnonymousFunctionDefinition (Expression ) istrue .- Return ?
NamedEvaluation ofExpression with argumentname.
- Return
InstantiateOrdinaryFunctionExpression ofFunctionExpression with argumentname.
- Return
InstantiateGeneratorFunctionExpression ofGeneratorExpression with argumentname.
- Return
InstantiateAsyncGeneratorFunctionExpression ofAsyncGeneratorExpression with argumentname.
- Return
InstantiateAsyncFunctionExpression ofAsyncFunctionExpression with argumentname.
- Return
InstantiateArrowFunctionExpression ofArrowFunction with argumentname.
- Return
InstantiateAsyncArrowFunctionExpression ofAsyncArrowFunction with argumentname.
- Letvalue be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined andname. - Setvalue.[[SourceText]] to the
source text matched by ClassExpression . - Returnvalue.
8.5 Contains
8.5.1 Static Semantics: Contains
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of Contains:
- For each child nodechild of this
Parse Node , do- Ifchild is an instance ofsymbol, return
true . - Ifchild is an instance of a nonterminal, then
- Letcontained be the result ofchild
Contains symbol. - Ifcontained is
true , returntrue .
- Letcontained be the result ofchild
- Ifchild is an instance ofsymbol, return
- Return
false .
- Return
false .
Static semantic rules that depend upon substructure generally do not look into function definitions.
- Ifsymbol is
ClassBody , returntrue . - Ifsymbol is
ClassHeritage , then- If
ClassHeritage is present, returntrue ; otherwise returnfalse .
- If
- If
ClassHeritage is present, then- If
ClassHeritage Contains symbol istrue , returntrue .
- If
- Return the result of
ComputedPropertyContains ofClassBody with argumentsymbol.
Static semantic rules that depend upon substructure generally do not look into class bodies except for
- Return
false .
Static semantic rules that depend upon substructure generally do not look intostatic initialization blocks.
- Ifsymbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - If
ArrowParameters Contains symbol istrue , returntrue . - Return
ConciseBody Contains symbol.
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Returnformals
Contains symbol.
- Ifsymbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - Return
AsyncConciseBody Contains symbol.
- Ifsymbol is not one of
NewTarget ,SuperProperty ,SuperCall ,super, orthis, returnfalse . - Lethead be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Ifhead
Contains symbol istrue , returntrue . - Return
AsyncConciseBody Contains symbol.
Contains is used to detectnew.target,this, andsuper usage within an
- Ifsymbol is
MethodDefinition , returntrue . - Return the result of
ComputedPropertyContains ofMethodDefinition with argumentsymbol.
- Return
false .
- If
MemberExpression Contains symbol istrue , returntrue . - Return
false .
- Ifsymbol is the
ReservedWord super, returntrue . - Return
false .
- If
CallExpression Contains symbol istrue , returntrue . - Return
false .
- Return
false .
- If
OptionalChain Contains symbol istrue , returntrue . - Return
false .
8.5.2 Static Semantics: ComputedPropertyContains
The
- Return
false .
- Return the result of
ComputedPropertyName Contains symbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argumentsymbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argumentsymbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argumentsymbol.
- LetinList be
ComputedPropertyContains ofClassElementList with argumentsymbol. - IfinList is
true , returntrue . - Return the result of
ComputedPropertyContains ofClassElement with argumentsymbol.
- Return
false .
- Return
false .
- Return the result of
ComputedPropertyContains ofClassElementName with argumentsymbol.
- Return the result of
ComputedPropertyContains ofClassElementName with argumentsymbol.
8.6 Miscellaneous
These operations are used in multiple places throughout the specification.
8.6.1 Runtime Semantics: InstantiateFunctionObject
The
- Return
InstantiateOrdinaryFunctionObject ofFunctionDeclaration with argumentsenv andprivateEnv.
- Return
InstantiateGeneratorFunctionObject ofGeneratorDeclaration with argumentsenv andprivateEnv.
- Return
InstantiateAsyncGeneratorFunctionObject ofAsyncGeneratorDeclaration with argumentsenv andprivateEnv.
- Return
InstantiateAsyncFunctionObject ofAsyncFunctionDeclaration with argumentsenv andprivateEnv.
8.6.2 Runtime Semantics: BindingInitialization
The
var statements and formal parameter lists of some
It is defined piecewise over the following productions:
- Letname be
StringValue ofIdentifier . - Return ?
InitializeBoundName (name,value,environment).
- Return ?
InitializeBoundName ("yield" ,value,environment).
- Return ?
InitializeBoundName ("await" ,value,environment).
- Perform ?
RequireObjectCoercible (value). - Return ?
BindingInitialization ofObjectBindingPattern with argumentsvalue andenvironment.
- LetiteratorRecord be ?
GetIterator (value,sync ). - Letresult be
Completion (IteratorBindingInitialization ofArrayBindingPattern with argumentsiteratorRecord andenvironment). - IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,result). - Return ? result.
- Return
unused .
- Perform ?
PropertyBindingInitialization ofBindingPropertyList with argumentsvalue andenvironment. - Return
unused .
- LetexcludedNames be a new empty
List . - Return ?
RestBindingInitialization ofBindingRestProperty with argumentsvalue,environment, andexcludedNames.
- LetexcludedNames be ?
PropertyBindingInitialization ofBindingPropertyList with argumentsvalue andenvironment. - Return ?
RestBindingInitialization ofBindingRestProperty with argumentsvalue,environment, andexcludedNames.
8.6.2.1 InitializeBoundName (name,value,environment )
The abstract operation InitializeBoundName takes argumentsname (a String),value (an
- Ifenvironment is not
undefined , then- Perform ! environment.InitializeBinding(name,value).
- Return
unused .
- Else,
- Letlhs be ?
ResolveBinding (name). - Return ?
PutValue (lhs,value).
- Letlhs be ?
8.6.3 Runtime Semantics: IteratorBindingInitialization
The
When
It is defined piecewise over the following productions:
- Return
unused .
- Return ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord.
- If
Elision is present, then- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord.
- Perform ?
- Return ?
IteratorBindingInitialization ofBindingRestElement with argumentsiteratorRecord andenvironment.
- Perform ?
IteratorBindingInitialization ofBindingElementList with argumentsiteratorRecord andenvironment. - Return ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord.
- Perform ?
IteratorBindingInitialization ofBindingElementList with argumentsiteratorRecord andenvironment. - If
Elision is present, then- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord.
- Perform ?
- Return ?
IteratorBindingInitialization ofBindingRestElement with argumentsiteratorRecord andenvironment.
- Perform ?
IteratorBindingInitialization ofBindingElementList with argumentsiteratorRecord andenvironment. - Return ?
IteratorBindingInitialization ofBindingElisionElement with argumentsiteratorRecord andenvironment.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord. - Return ?
IteratorBindingInitialization ofBindingElement with argumentsiteratorRecord andenvironment.
- LetbindingId be
StringValue ofBindingIdentifier . - Letlhs be ?
ResolveBinding (bindingId,environment). - Letv be
undefined . - IfiteratorRecord.[[Done]] is
false , then- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Setv tonext.
- Letnext be ?
- If
Initializer is present andv isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Setv to ?
NamedEvaluation ofInitializer with argumentbindingId.
- Setv to ?
- Else,
- LetdefaultValue be ?
Evaluation ofInitializer . - Setv to ?
GetValue (defaultValue).
- LetdefaultValue be ?
- If
- Ifenvironment is
undefined , return ?PutValue (lhs,v). - Return ?
InitializeReferencedBinding (lhs,v).
- Letv be
undefined . - IfiteratorRecord.[[Done]] is
false , then- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Setv tonext.
- Letnext be ?
- If
Initializer is present andv isundefined , then- LetdefaultValue be ?
Evaluation ofInitializer . - Setv to ?
GetValue (defaultValue).
- LetdefaultValue be ?
- Return ?
BindingInitialization ofBindingPattern with argumentsv andenvironment.
- Letlhs be ?
ResolveBinding (StringValue ofBindingIdentifier ,environment). - LetA be !
ArrayCreate (0). - Letn be 0.
- Repeat,
- Letnext be
done . - IfiteratorRecord.[[Done]] is
false , then- Setnext to ?
IteratorStepValue (iteratorRecord).
- Setnext to ?
- Ifnext is
done , then- Ifenvironment is
undefined , return ?PutValue (lhs,A). - Return ?
InitializeReferencedBinding (lhs,A).
- Ifenvironment is
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),next). - Setn ton + 1.
- Letnext be
- LetA be !
ArrayCreate (0). - Letn be 0.
- Repeat,
- Letnext be
done . - IfiteratorRecord.[[Done]] is
false , then- Setnext to ?
IteratorStepValue (iteratorRecord).
- Setnext to ?
- Ifnext is
done , then- Return ?
BindingInitialization ofBindingPattern with argumentsA andenvironment.
- Return ?
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),next). - Setn ton + 1.
- Letnext be
- Return
unused .
- Perform ?
IteratorBindingInitialization ofFormalParameterList with argumentsiteratorRecord andenvironment. - Return ?
IteratorBindingInitialization ofFunctionRestParameter with argumentsiteratorRecord andenvironment.
- Perform ?
IteratorBindingInitialization ofFormalParameterList with argumentsiteratorRecord andenvironment. - Return ?
IteratorBindingInitialization ofFormalParameter with argumentsiteratorRecord andenvironment.
- Letv be
undefined . Assert :iteratorRecord.[[Done]] isfalse .- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Setv tonext.
- Return ?
BindingInitialization ofBindingIdentifier with argumentsv andenvironment.
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
IteratorBindingInitialization offormals with argumentsiteratorRecord andenvironment.
- Letv be
undefined . Assert :iteratorRecord.[[Done]] isfalse .- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Setv tonext.
- Return ?
BindingInitialization ofBindingIdentifier with argumentsv andenvironment.
8.6.4 Static Semantics: AssignmentTargetType
The
- If this
IdentifierReference is contained instrict mode code andStringValue ofIdentifier is either"eval" or"arguments" , returninvalid . - Return
simple .
- Return
simple .
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
AssignmentTargetType ofexpr.
- Return
invalid .
8.6.5 Static Semantics: PropName
The
- Return
StringValue ofIdentifierReference .
- Return
empty .
- Return
PropName ofPropertyName .
- Return
StringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
- Letnbr be the
NumericValue ofNumericLiteral . - Return !
ToString (nbr).
- Return
empty .
- Return
PropName ofClassElementName .
- Return
PropName ofClassElementName .
- Return
PropName ofClassElementName .
- Return
empty .
- Return
empty .
- Return
PropName ofClassElementName .
- Return
PropName ofClassElementName .
- Return
empty .
9 Executable Code and Execution Contexts
9.1 Environment Records
Environment Record is a specification type used to define the association of
Every Environment Record has an[[OuterEnv]] field, which is either
Environment Records are purely specification mechanisms and need not correspond to any specific artefact of an ECMAScript implementation. It is impossible for an ECMAScript program to directly access or manipulate such values.
9.1.1 The Environment Record Type Hierarchy
Environment Record (abstract)A
Declarative Environment Record is used to define the effect of ECMAScript language syntactic elements such asFunctionDeclaration s,VariableDeclaration s, andCatch clauses that directly associate identifier bindings withECMAScript language values .A
Function Environment Record corresponds to the invocation of an ECMAScriptfunction object , and contains bindings for the top-level declarations within that function. It may establish a newthisbinding. It also captures the state necessary to supportsupermethod invocations.A
Module Environment Record contains the bindings for the top-level declarations of aModule . It also contains the bindings that are explicitly imported by theModule . Its[[OuterEnv]] is aGlobal Environment Record .
An
Object Environment Record is used to define the effect of ECMAScript elements such asWithStatement that associate identifier bindings with the properties of some object.A
Global Environment Record is used forScript global declarations. It does not have an outer environment; its[[OuterEnv]] isnull . It may be prepopulated with identifier bindings and it includes an associatedglobal object whose properties provide some of the global environment's identifier bindings. As ECMAScript code is executed, additional properties may be added to theglobal object and the initial properties may be modified.
The
| Method | Purpose |
|---|---|
| HasBinding(N) | Determine if an |
| CreateMutableBinding(N, D) | Create a new but uninitialized mutable binding in an |
| CreateImmutableBinding(N, S) | Create a new but uninitialized immutable binding in an |
| InitializeBinding(N, V) | Set the value of an already existing but uninitialized binding in an |
| SetMutableBinding(N, V, S) | Set the value of an already existing mutable binding in an |
| GetBindingValue(N, S) | Returns the value of an already existing binding from an |
| DeleteBinding(N) | Delete a binding from an |
| HasThisBinding() | Determine if anthis binding. Return |
| HasSuperBinding() | Determine if ansuper method binding. Return |
| WithBaseObject() | If thiswith statement, return the with object. Otherwise, return |
9.1.1.1 Declarative Environment Records
EachDeclarative Environment Record is associated with an ECMAScript program scope containing variable, constant, let, class, module, import, and/or function declarations. A Declarative Environment Record binds the set of identifiers defined by the declarations contained within its scope.
The behaviour of the concrete specification methods for Declarative Environment Records is defined by the following algorithms.
9.1.1.1.1 HasBinding (N )
The HasBinding concrete method of a
- IfenvRec has a binding forN, return
true . - Return
false .
9.1.1.1.2 CreateMutableBinding (N,D )
The CreateMutableBinding concrete method of a
Assert :envRec does not already have a binding forN.- Create a mutable binding inenvRec forN and record that it is uninitialized. IfD is
true , record that the newly created binding may be deleted by a subsequent DeleteBinding call. - Return
unused .
9.1.1.1.3 CreateImmutableBinding (N,S )
The CreateImmutableBinding concrete method of a
Assert :envRec does not already have a binding forN.- Create an immutable binding inenvRec forN and record that it is uninitialized. IfS is
true , record that the newly created binding is a strict binding. - Return
unused .
9.1.1.1.4 InitializeBinding (N,V )
The InitializeBinding concrete method of a
Assert :envRec must have an uninitialized binding forN.- Set the bound value forN inenvRec toV.
Record that the binding forN inenvRec has been initialized.- Return
unused .
9.1.1.1.5 SetMutableBinding (N,V,S )
The SetMutableBinding concrete method of a
- IfenvRec does not have a binding forN, then
- IfS is
true , throw aReferenceError exception. - Perform ! envRec.CreateMutableBinding(N,
true ). - Perform ! envRec.InitializeBinding(N,V).
- Return
unused .
- IfS is
- If the binding forN inenvRec is a strict binding, setS to
true . - If the binding forN inenvRec has not yet been initialized, then
- Throw a
ReferenceError exception.
- Throw a
- Else if the binding forN inenvRec is a mutable binding, then
- Change its bound value toV.
- Else,
Assert : This is an attempt to change the value of an immutable binding.- IfS is
true , throw aTypeError exception.
- Return
unused .
An example of ECMAScript code that results in a missing binding at step
functionf() {eval("var x; x = (delete x, 0);"); }9.1.1.1.6 GetBindingValue (N,S )
The GetBindingValue concrete method of a
Assert :envRec has a binding forN.- If the binding forN inenvRec is an uninitialized binding, throw a
ReferenceError exception. - Return the value currently bound toN inenvRec.
9.1.1.1.7 DeleteBinding (N )
The DeleteBinding concrete method of a
Assert :envRec has a binding forN.- If the binding forN inenvRec cannot be deleted, return
false . - Remove the binding forN fromenvRec.
- Return
true .
9.1.1.1.8 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
false .
A regularthis binding.
9.1.1.1.9 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- Return
false .
A regularsuper binding.
9.1.1.1.10 WithBaseObject ( )
The WithBaseObject concrete method of a
- Return
undefined .
9.1.1.2 Object Environment Records
EachObject Environment Record is associated with an object called itsbinding object. An Object Environment Record binds the set of string identifier names that directly correspond to the property names of its binding object.
Object Environment Records created forwith statements (
Object Environment Records have the additional state fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[BindingObject]] | an Object | The binding object of this |
| [[IsWithEnvironment]] | a Boolean | Indicates whether thiswith statement. |
The behaviour of the concrete specification methods for Object Environment Records is defined by the following algorithms.
9.1.1.2.1 HasBinding (N )
The HasBinding concrete method of an
- LetbindingObject beenvRec.[[BindingObject]].
- LetfoundBinding be ?
HasProperty (bindingObject,N). - IffoundBinding is
false , returnfalse . - IfenvRec.[[IsWithEnvironment]] is
false , returntrue . - Letunscopables be ?
Get (bindingObject,@@unscopables ). - Ifunscopables
is an Object , then - Return
true .
9.1.1.2.2 CreateMutableBinding (N,D )
The CreateMutableBinding concrete method of an
- LetbindingObject beenvRec.[[BindingObject]].
- Perform ?
DefinePropertyOrThrow (bindingObject,N, PropertyDescriptor {[[Value]]:undefined ,[[Writable]]:true ,[[Enumerable]]:true ,[[Configurable]]:D }). - Return
unused .
NormallyenvRec will not have a binding forN but if it does, the semantics of
9.1.1.2.3 CreateImmutableBinding (N,S )
The CreateImmutableBinding concrete method of an
9.1.1.2.4 InitializeBinding (N,V )
The InitializeBinding concrete method of an
- Perform ? envRec.SetMutableBinding(N,V,
false ). - Return
unused .
In this specification, all uses of CreateMutableBinding for
9.1.1.2.5 SetMutableBinding (N,V,S )
The SetMutableBinding concrete method of an
- LetbindingObject beenvRec.[[BindingObject]].
- LetstillExists be ?
HasProperty (bindingObject,N). - IfstillExists is
false andS istrue , throw aReferenceError exception. - Perform ?
Set (bindingObject,N,V,S). - Return
unused .
9.1.1.2.6 GetBindingValue (N,S )
The GetBindingValue concrete method of an
- LetbindingObject beenvRec.[[BindingObject]].
- Letvalue be ?
HasProperty (bindingObject,N). - Ifvalue is
false , then- IfS is
false , returnundefined ; otherwise throw aReferenceError exception.
- IfS is
- Return ?
Get (bindingObject,N).
9.1.1.2.7 DeleteBinding (N )
The DeleteBinding concrete method of an
- LetbindingObject beenvRec.[[BindingObject]].
- Return ? bindingObject.[[Delete]](N).
9.1.1.2.8 HasThisBinding ( )
The HasThisBinding concrete method of an
- Return
false .
this binding.
9.1.1.2.9 HasSuperBinding ( )
The HasSuperBinding concrete method of an
- Return
false .
super binding.
9.1.1.2.10 WithBaseObject ( )
The WithBaseObject concrete method of an
- IfenvRec.[[IsWithEnvironment]] is
true , returnenvRec.[[BindingObject]]. - Otherwise, return
undefined .
9.1.1.3 Function Environment Records
AFunction Environment Record is athis binding. If a function is not ansuper, its Function Environment Record also contains the state that is used to performsuper method invocations from within the function.
Function Environment Records have the additional state fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ThisValue]] | an | This is the |
| [[ThisBindingStatus]] | If the value is | |
| [[FunctionObject]] | an ECMAScript | The |
| [[NewTarget]] | an Object or | If this |
Function Environment Records support all of the
| Method | Purpose |
|---|---|
| BindThisValue(V) | Set the[[ThisValue]] and record that it has been initialized. |
| GetThisBinding() | Return the value of thisthis binding. Throws athis binding has not been initialized. |
| GetSuperBase() | Return the object that is the base forsuper property accesses bound in this |
The behaviour of the additional concrete specification methods for Function Environment Records is defined by the following algorithms:
9.1.1.3.1 BindThisValue (V )
The BindThisValue concrete method of a
Assert :envRec.[[ThisBindingStatus]] is notlexical .- IfenvRec.[[ThisBindingStatus]] is
initialized , throw aReferenceError exception. - SetenvRec.[[ThisValue]] toV.
- SetenvRec.[[ThisBindingStatus]] to
initialized . - ReturnV.
9.1.1.3.2 HasThisBinding ( )
The HasThisBinding concrete method of a
- IfenvRec.[[ThisBindingStatus]] is
lexical , returnfalse ; otherwise, returntrue .
9.1.1.3.3 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- IfenvRec.[[ThisBindingStatus]] is
lexical , returnfalse . - IfenvRec.[[FunctionObject]].[[HomeObject]] is
undefined , returnfalse ; otherwise, returntrue .
9.1.1.3.4 GetThisBinding ( )
The GetThisBinding concrete method of a
Assert :envRec.[[ThisBindingStatus]] is notlexical .- IfenvRec.[[ThisBindingStatus]] is
uninitialized , throw aReferenceError exception. - ReturnenvRec.[[ThisValue]].
9.1.1.3.5 GetSuperBase ( )
The GetSuperBase concrete method of a
- Lethome beenvRec.[[FunctionObject]].[[HomeObject]].
- Ifhome is
undefined , returnundefined . Assert :homeis an Object .- Return ? home.[[GetPrototypeOf]]().
9.1.1.4 Global Environment Records
AGlobal Environment Record is used to represent the outer most scope that is shared by all of the ECMAScript
A Global Environment Record is logically a single record but it is specified as a composite encapsulating an
Properties may be created directly on a
Global Environment Records have the additional fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ObjectRecord]] | an | Binding object is the |
| [[GlobalThisValue]] | an Object | The value returned bythis in global scope. |
| [[DeclarativeRecord]] | a | |
| [[VarNames]] | a | The string names bound by |
| Method | Purpose |
|---|---|
| GetThisBinding() | Return the value of thisthis binding. |
| HasVarDeclaration (N) | Determines if the argument identifier has a binding in this |
| HasLexicalDeclaration (N) | Determines if the argument identifier has a binding in this |
| HasRestrictedGlobalProperty (N) | Determines if the argument is the name of a |
| CanDeclareGlobalVar (N) | Determines if a corresponding CreateGlobalVarBinding call would succeed if called for the same argumentN. |
| CanDeclareGlobalFunction (N) | Determines if a corresponding CreateGlobalFunctionBinding call would succeed if called for the same argumentN. |
| CreateGlobalVarBinding(N, D) | Used to create and initialize tovar binding in the[[ObjectRecord]] component of avar. The String valueN is the bound name. IfD is |
| CreateGlobalFunctionBinding(N, V, D) | Create and initialize a globalfunction binding in the[[ObjectRecord]] component of afunction. The String valueN is the bound name.V is the initialization value. If the Boolean argumentD is |
The behaviour of the concrete specification methods for Global Environment Records is defined by the following algorithms.
9.1.1.4.1 HasBinding (N )
The HasBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , returntrue . - LetObjRec beenvRec.[[ObjectRecord]].
- Return ? ObjRec.HasBinding(N).
9.1.1.4.2 CreateMutableBinding (N,D )
The CreateMutableBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , throw aTypeError exception. - Return ! DclRec.CreateMutableBinding(N,D).
9.1.1.4.3 CreateImmutableBinding (N,S )
The CreateImmutableBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , throw aTypeError exception. - Return ! DclRec.CreateImmutableBinding(N,S).
9.1.1.4.4 InitializeBinding (N,V )
The InitializeBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ! DclRec.InitializeBinding(N,V).
Assert : If the binding exists, it must be in theObject Environment Record .- LetObjRec beenvRec.[[ObjectRecord]].
- Return ? ObjRec.InitializeBinding(N,V).
9.1.1.4.5 SetMutableBinding (N,V,S )
The SetMutableBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ? DclRec.SetMutableBinding(N,V,S).
- LetObjRec beenvRec.[[ObjectRecord]].
- Return ? ObjRec.SetMutableBinding(N,V,S).
9.1.1.4.6 GetBindingValue (N,S )
The GetBindingValue concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ? DclRec.GetBindingValue(N,S).
- LetObjRec beenvRec.[[ObjectRecord]].
- Return ? ObjRec.GetBindingValue(N,S).
9.1.1.4.7 DeleteBinding (N )
The DeleteBinding concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- If ! DclRec.HasBinding(N) is
true , then- Return ! DclRec.DeleteBinding(N).
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LetexistingProp be ?
HasOwnProperty (globalObject,N). - IfexistingProp is
true , then- Letstatus be ? ObjRec.DeleteBinding(N).
- Ifstatus is
true andenvRec.[[VarNames]] containsN, then- RemoveN fromenvRec.[[VarNames]].
- Returnstatus.
- Return
true .
9.1.1.4.8 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
true .
this binding.
9.1.1.4.9 HasSuperBinding ( )
The HasSuperBinding concrete method of a
- Return
false .
super binding.
9.1.1.4.10 WithBaseObject ( )
The WithBaseObject concrete method of a
- Return
undefined .
9.1.1.4.11 GetThisBinding ( )
The GetThisBinding concrete method of a
- ReturnenvRec.[[GlobalThisValue]].
9.1.1.4.12 HasVarDeclaration (N )
The HasVarDeclaration concrete method of a
- LetvarDeclaredNames beenvRec.[[VarNames]].
- IfvarDeclaredNames containsN, return
true . - Return
false .
9.1.1.4.13 HasLexicalDeclaration (N )
The HasLexicalDeclaration concrete method of a
- LetDclRec beenvRec.[[DeclarativeRecord]].
- Return ! DclRec.HasBinding(N).
9.1.1.4.14 HasRestrictedGlobalProperty (N )
The HasRestrictedGlobalProperty concrete method of a
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LetexistingProp be ? globalObject.[[GetOwnProperty]](N).
- IfexistingProp is
undefined , returnfalse . - IfexistingProp.[[Configurable]] is
true , returnfalse . - Return
true .
Properties may exist upon a
9.1.1.4.15 CanDeclareGlobalVar (N )
The CanDeclareGlobalVar concrete method of a
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LethasProperty be ?
HasOwnProperty (globalObject,N). - IfhasProperty is
true , returntrue . - Return ?
IsExtensible (globalObject).
9.1.1.4.16 CanDeclareGlobalFunction (N )
The CanDeclareGlobalFunction concrete method of a
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LetexistingProp be ? globalObject.[[GetOwnProperty]](N).
- IfexistingProp is
undefined , return ?IsExtensible (globalObject). - IfexistingProp.[[Configurable]] is
true , returntrue . - If
IsDataDescriptor (existingProp) istrue andexistingProp has attribute values {[[Writable]]:true ,[[Enumerable]]:true }, returntrue . - Return
false .
9.1.1.4.17 CreateGlobalVarBinding (N,D )
The CreateGlobalVarBinding concrete method of a
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LethasProperty be ?
HasOwnProperty (globalObject,N). - Letextensible be ?
IsExtensible (globalObject). - IfhasProperty is
false andextensible istrue , then- Perform ? ObjRec.CreateMutableBinding(N,D).
- Perform ? ObjRec.InitializeBinding(N,
undefined ).
- IfenvRec.[[VarNames]] does not containN, then
- AppendN toenvRec.[[VarNames]].
- Return
unused .
9.1.1.4.18 CreateGlobalFunctionBinding (N,V,D )
The CreateGlobalFunctionBinding concrete method of a
- LetObjRec beenvRec.[[ObjectRecord]].
- LetglobalObject beObjRec.[[BindingObject]].
- LetexistingProp be ? globalObject.[[GetOwnProperty]](N).
- IfexistingProp is
undefined orexistingProp.[[Configurable]] istrue , then- Letdesc be the PropertyDescriptor {[[Value]]:V,[[Writable]]:
true ,[[Enumerable]]:true ,[[Configurable]]:D }.
- Letdesc be the PropertyDescriptor {[[Value]]:V,[[Writable]]:
- Else,
- Letdesc be the PropertyDescriptor {[[Value]]:V }.
- Perform ?
DefinePropertyOrThrow (globalObject,N,desc). - Perform ?
Set (globalObject,N,V,false ). - IfenvRec.[[VarNames]] does not containN, then
- AppendN toenvRec.[[VarNames]].
- Return
unused .
Global function declarations are always represented as own properties of the
9.1.1.5 Module Environment Records
AModule Environment Record is a
Module Environment Records support all of the
| Method | Purpose |
|---|---|
| CreateImportBinding(N, M, N2) | Create an immutable indirect binding in a |
| GetThisBinding() | Return the value of thisthis binding. |
The behaviour of the additional concrete specification methods for Module Environment Records are defined by the following algorithms:
9.1.1.5.1 GetBindingValue (N,S )
The GetBindingValue concrete method of a
Assert :S istrue .Assert :envRec has a binding forN.- If the binding forN is an indirect binding, then
- LetM andN2 be the indirection values provided when this binding forN was created.
- LettargetEnv beM.[[Environment]].
- IftargetEnv is
empty , throw aReferenceError exception. - Return ? targetEnv.GetBindingValue(N2,
true ).
- If the binding forN inenvRec is an uninitialized binding, throw a
ReferenceError exception. - Return the value currently bound toN inenvRec.
S will always be
9.1.1.5.2 DeleteBinding (N )
The DeleteBinding concrete method of a
9.1.1.5.3 HasThisBinding ( )
The HasThisBinding concrete method of a
- Return
true .
this binding.
9.1.1.5.4 GetThisBinding ( )
The GetThisBinding concrete method of a
- Return
undefined .
9.1.1.5.5 CreateImportBinding (N,M,N2 )
The CreateImportBinding concrete method of a
9.1.2 Environment Record Operations
The following
9.1.2.1 GetIdentifierReference (env,name,strict )
The abstract operation GetIdentifierReference takes argumentsenv (an
- Ifenv is
null , then- Return the
Reference Record {[[Base]]:unresolvable ,[[ReferencedName]]:name,[[Strict]]:strict,[[ThisValue]]:empty }.
- Return the
- Letexists be ? env.HasBinding(name).
- Ifexists is
true , then- Return the
Reference Record {[[Base]]:env,[[ReferencedName]]:name,[[Strict]]:strict,[[ThisValue]]:empty }.
- Return the
- Else,
- Letouter beenv.[[OuterEnv]].
- Return ?
GetIdentifierReference (outer,name,strict).
9.1.2.2 NewDeclarativeEnvironment (E )
The abstract operation NewDeclarativeEnvironment takes argumentE (an
- Letenv be a new
Declarative Environment Record containing no bindings. - Setenv.[[OuterEnv]] toE.
- Returnenv.
9.1.2.3 NewObjectEnvironment (O,W,E )
The abstract operation NewObjectEnvironment takes argumentsO (an Object),W (a Boolean), andE (an
- Letenv be a new
Object Environment Record . - Setenv.[[BindingObject]] toO.
- Setenv.[[IsWithEnvironment]] toW.
- Setenv.[[OuterEnv]] toE.
- Returnenv.
9.1.2.4 NewFunctionEnvironment (F,newTarget )
The abstract operation NewFunctionEnvironment takes argumentsF (an ECMAScript
- Letenv be a new
Function Environment Record containing no bindings. - Setenv.[[FunctionObject]] toF.
- IfF.[[ThisMode]] is
lexical , setenv.[[ThisBindingStatus]] tolexical . - Else, setenv.[[ThisBindingStatus]] to
uninitialized . - Setenv.[[NewTarget]] tonewTarget.
- Setenv.[[OuterEnv]] toF.[[Environment]].
- Returnenv.
9.1.2.5 NewGlobalEnvironment (G,thisValue )
The abstract operation NewGlobalEnvironment takes argumentsG (an Object) andthisValue (an Object) and returns a
- LetobjRec be
NewObjectEnvironment (G,false ,null ). - LetdclRec be
NewDeclarativeEnvironment (null ). - Letenv be a new
Global Environment Record . - Setenv.[[ObjectRecord]] toobjRec.
- Setenv.[[GlobalThisValue]] tothisValue.
- Setenv.[[DeclarativeRecord]] todclRec.
- Setenv.[[VarNames]] to a new empty
List . - Setenv.[[OuterEnv]] to
null . - Returnenv.
9.1.2.6 NewModuleEnvironment (E )
The abstract operation NewModuleEnvironment takes argumentE (an
- Letenv be a new
Module Environment Record containing no bindings. - Setenv.[[OuterEnv]] toE.
- Returnenv.
9.2 PrivateEnvironment Records
APrivateEnvironment Record is a specification mechanism used to track
Each
| Field Name | Value Type | Meaning |
|---|---|---|
| [[OuterPrivateEnvironment]] | a | The |
| [[Names]] | a | The |
9.2.1 PrivateEnvironment Record Operations
The following
9.2.1.1 NewPrivateEnvironment (outerPrivEnv )
The abstract operation NewPrivateEnvironment takes argumentouterPrivEnv (a
- Letnames be a new empty
List . - Return the
PrivateEnvironment Record {[[OuterPrivateEnvironment]]:outerPrivEnv,[[Names]]:names }.
9.2.1.2 ResolvePrivateIdentifier (privEnv,identifier )
The abstract operation ResolvePrivateIdentifier takes argumentsprivEnv (a
- Letnames beprivEnv.[[Names]].
- For each
Private Name pn ofnames, do- Ifpn.[[Description]] isidentifier, then
- Returnpn.
- Ifpn.[[Description]] isidentifier, then
- LetouterPrivEnv beprivEnv.[[OuterPrivateEnvironment]].
Assert :outerPrivEnv is notnull .- Return
ResolvePrivateIdentifier (outerPrivEnv,identifier).
9.3 Realms
Before it is evaluated, all ECMAScript code must be associated with arealm. Conceptually, a
A
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] | an | The |
| [[Intrinsics]] | a | The intrinsic values used by code associated with this |
| [[GlobalObject]] | an Object or | The |
| [[GlobalEnv]] | a | The global environment for this |
| [[TemplateMap]] | a | Template objects are canonicalized separately for each Once a |
| [[LoadedModules]] | a | A map from the specifier strings imported by this As mentioned in import() expression in a context where there is no |
| [[HostDefined]] | anything (default value is | Field reserved for use by |
9.3.1 CreateRealm ( )
The abstract operation CreateRealm takes no arguments and returns a
- LetrealmRec be a new
Realm Record . - Perform
CreateIntrinsics (realmRec). - SetrealmRec.[[AgentSignifier]] to
AgentSignifier (). - SetrealmRec.[[GlobalObject]] to
undefined . - SetrealmRec.[[GlobalEnv]] to
undefined . - SetrealmRec.[[TemplateMap]] to a new empty
List . - ReturnrealmRec.
9.3.2 CreateIntrinsics (realmRec )
The abstract operation CreateIntrinsics takes argumentrealmRec (a
- SetrealmRec.[[Intrinsics]] to a new
Record . - Set fields ofrealmRec.[[Intrinsics]] with the values listed in
Table 6 . The field names are the names listed in column one of the table. The value of each field is a new object value fully and recursively populated with property values as defined by the specification of each object in clauses19 through28 . All object property values are newly created object values. All values that are built-infunction objects are created by performingCreateBuiltinFunction (steps,length,name,slots,realmRec,prototype) wheresteps is the definition of that function provided by this specification,name is the initial value of the function's"name" property,length is the initial value of the function's"length" property,slots is a list of the names, if any, of the function's specified internal slots, andprototype is the specified value of the function's[[Prototype]] internal slot. The creation of the intrinsics and their properties must be ordered to avoid any dependencies upon objects that have not yet been created. - Perform
AddRestrictedFunctionProperties (realmRec.[[Intrinsics]].[[%Function.prototype% ]],realmRec). - Return
unused .
9.3.3 SetRealmGlobalObject (realmRec,globalObj,thisValue )
The abstract operation SetRealmGlobalObject takes argumentsrealmRec (a
- IfglobalObj is
undefined , then- Letintrinsics berealmRec.[[Intrinsics]].
- SetglobalObj to
OrdinaryObjectCreate (intrinsics.[[%Object.prototype% ]]).
Assert :globalObjis an Object .- IfthisValue is
undefined , setthisValue toglobalObj. - SetrealmRec.[[GlobalObject]] toglobalObj.
- LetnewGlobalEnv be
NewGlobalEnvironment (globalObj,thisValue). - SetrealmRec.[[GlobalEnv]] tonewGlobalEnv.
- Return
unused .
9.3.4 SetDefaultGlobalBindings (realmRec )
The abstract operation SetDefaultGlobalBindings takes argumentrealmRec (a
- Letglobal berealmRec.[[GlobalObject]].
- For each property of the Global Object specified in clause
19 , do- Letname be the String value of the
property name . - Letdesc be the fully populated data
Property Descriptor for the property, containing the specified attributes for the property. For properties listed in19.2 ,19.3 , or19.4 the value of the[[Value]] attribute is the corresponding intrinsic object fromrealmRec. - Perform ?
DefinePropertyOrThrow (global,name,desc).
- Letname be the String value of the
- Returnglobal.
9.4 Execution Contexts
Anexecution context is a specification device that is used to track the runtime evaluation of code by an ECMAScript implementation. At any point in time, there is at most one execution context per
Theexecution context stack is used to track execution contexts. The
An execution context contains whatever implementation specific state is necessary to track the execution progress of its associated code. Each execution context has at least the state components listed in
| Component | Purpose |
|---|---|
| code evaluation state | Any state needed to perform, suspend, and resume evaluation of the code associated with this |
| Function | If this |
| The | |
| ScriptOrModule | The |
The value of the
ECMAScript code execution contexts have the additional state components listed in
| Component | Purpose |
|---|---|
| LexicalEnvironment | Identifies the |
| VariableEnvironment | Identifies the |
| PrivateEnvironment | Identifies the |
The LexicalEnvironment and VariableEnvironment components of an execution context are always
Execution contexts representing the evaluation of Generators have the additional state components listed in
| Component | Purpose |
|---|---|
| Generator | The Generator that this |
In most situations only the
An execution context is purely a specification mechanism and need not correspond to any particular artefact of an ECMAScript implementation. It is impossible for ECMAScript code to directly access or observe an execution context.
9.4.1 GetActiveScriptOrModule ( )
The abstract operation GetActiveScriptOrModule takes no arguments and returns a
- If the
execution context stack is empty, returnnull . - Letec be the topmost
execution context on theexecution context stack whose ScriptOrModule component is notnull . - If no such
execution context exists, returnnull . Otherwise, returnec's ScriptOrModule.
9.4.2 ResolveBinding (name [ ,env ] )
The abstract operation ResolveBinding takes argumentname (a String) and optional argumentenv (an
- Ifenv is not present orenv is
undefined , then- Setenv to the
running execution context 's LexicalEnvironment.
- Setenv to the
Assert :env is anEnvironment Record .- If the
source text matched by the syntactic production that is being evaluated is contained instrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
GetIdentifierReference (env,name,strict).
The result of ResolveBinding is always a
9.4.3 GetThisEnvironment ( )
The abstract operation GetThisEnvironment takes no arguments and returns anthis. It performs the following steps when called:
- Letenv be the
running execution context 's LexicalEnvironment. - Repeat,
- Letexists beenv.HasThisBinding().
- Ifexists is
true , returnenv. - Letouter beenv.[[OuterEnv]].
Assert :outer is notnull .- Setenv toouter.
The loop in stepthis binding.
9.4.4 ResolveThisBinding ( )
The abstract operation ResolveThisBinding takes no arguments and returns either athis using the LexicalEnvironment of the
- LetenvRec be
GetThisEnvironment (). - Return ? envRec.GetThisBinding().
9.4.5 GetNewTarget ( )
The abstract operation GetNewTarget takes no arguments and returns an Object or
- LetenvRec be
GetThisEnvironment (). Assert :envRec has a[[NewTarget]] field.- ReturnenvRec.[[NewTarget]].
9.4.6 GetGlobalObject ( )
The abstract operation GetGlobalObject takes no arguments and returns an Object. It returns the
- LetcurrentRealm be
the current Realm Record . - ReturncurrentRealm.[[GlobalObject]].
9.5 Jobs and Host Operations to Enqueue Jobs
AJob is an
- At some future point in time, when there is no running context in the
agent for which the job is scheduled and thatagent 'sexecution context stack is empty, the implementation must:- Perform any
host-defined preparation steps. Invoke theJob Abstract Closure .- Perform any
host-defined cleanup steps, after which theexecution context stack must be empty.
- Perform any
- Only one
Job may be actively undergoing evaluation at any point in time in anagent . - Once evaluation of a
Job starts, it must run to completion before evaluation of any otherJob starts in anagent . - The
Abstract Closure must return anormal completion , implementing its own handling of errors.
At any particular time,scriptOrModule (a
GetActiveScriptOrModule () isscriptOrModule.- IfscriptOrModule is a
Script Record orModule Record , letec be the topmostexecution context on theexecution context stack whose ScriptOrModule component isscriptOrModule. TheRealm component ofec isscriptOrModule.[[Realm]].
At any particular time, an execution isprepared to evaluate ECMAScript code if all of the following conditions are true:
- The
execution context stack is not empty. - The
Realm component of the topmostexecution context on theexecution context stack is aRealm Record .
The specific choice of
Particular kinds of
9.5.1 JobCallback Records
AJobCallback Record is a
The WHATWG HTML specification (https://html.spec.whatwg.org/), for example, uses the
JobCallback Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Callback]] | a | The function to invoke when the |
| [[HostDefined]] | anything (default value is | Field reserved for use by |
9.5.2 HostMakeJobCallback (callback )
The
An implementation of HostMakeJobCallback must conform to the following requirements:
- It must return a
JobCallback Record whose[[Callback]] field iscallback.
The default implementation of HostMakeJobCallback performs the following steps when called:
- Return the
JobCallback Record {[[Callback]]:callback,[[HostDefined]]:empty }.
ECMAScript
This is called at the time that the callback is passed to the function that is responsible for its being eventually scheduled and run. For example,promise.then(thenAction) calls MakeJobCallback onthenAction at the time of invokingPromise.prototype.then, not at the time of scheduling the reaction
9.5.3 HostCallJobCallback (jobCallback,V,argumentsList )
The
An implementation of HostCallJobCallback must conform to the following requirements:
- It must perform and return the result of
Call (jobCallback.[[Callback]],V,argumentsList).
This requirement means that
The default implementation of HostCallJobCallback performs the following steps when called:
Assert :IsCallable (jobCallback.[[Callback]]) istrue .- Return ?
Call (jobCallback.[[Callback]],V,argumentsList).
ECMAScript
9.5.4 HostEnqueueGenericJob (job,realm )
The
An implementation of HostEnqueueGenericJob must conform to the requirements in
9.5.5 HostEnqueuePromiseJob (job,realm )
The
An implementation of HostEnqueuePromiseJob must conform to the requirements in
- Ifrealm is not
null , each timejob is invoked the implementation must performimplementation-defined steps such that execution isprepared to evaluate ECMAScript code at the time ofjob's invocation. - LetscriptOrModule be
GetActiveScriptOrModule () at the time HostEnqueuePromiseJob is invoked. Ifrealm is notnull , each timejob is invoked the implementation must performimplementation-defined steps such thatscriptOrModule is theactive script or module at the time ofjob's invocation. Jobs must run in the same order as the HostEnqueuePromiseJob invocations that scheduled them.
Therealm for
9.5.6 HostEnqueueTimeoutJob (timeoutJob,realm,milliseconds )
The
An implementation of HostEnqueueTimeoutJob must conform to the requirements in
9.6 InitializeHostDefinedRealm ( )
The abstract operation InitializeHostDefinedRealm takes no arguments and returns either a
- Letrealm be
CreateRealm (). - LetnewContext be a new
execution context . - Set the Function ofnewContext to
null . - Set the
Realm ofnewContext torealm. - Set the ScriptOrModule ofnewContext to
null . - PushnewContext onto the
execution context stack ;newContext is now therunning execution context . - If the
host requires use of anexotic object to serve asrealm'sglobal object , letglobal be such an object created in ahost-defined manner. Otherwise, letglobal beundefined , indicating that anordinary object should be created as theglobal object . - If the
host requires that thethisbinding inrealm's global scope return an object other than theglobal object , letthisValue be such an object created in ahost-defined manner. Otherwise, letthisValue beundefined , indicating thatrealm's globalthisbinding should be theglobal object . - Perform
SetRealmGlobalObject (realm,global,thisValue). - LetglobalObj be ?
SetDefaultGlobalBindings (realm). - Create any
host-defined global object properties onglobalObj. - Return
unused .
9.7 Agents
Anagent comprises a set of ECMAScript
An
Some web browsers share a single
While an
Anagent signifier is a globally-unique opaque value used to identify an
| Field Name | Value | Meaning |
|---|---|---|
| [[LittleEndian]] | a Boolean | The default value computed for theisLittleEndian parameter when it is needed by the algorithms |
| [[CanBlock]] | a Boolean | Determines whether the |
| [[Signifier]] | an | Uniquely identifies the |
| [[IsLockFree1]] | a Boolean | |
| [[IsLockFree2]] | a Boolean | |
| [[IsLockFree8]] | a Boolean | |
| [[CandidateExecution]] | a | See the |
| [[KeptAlive]] | a | Initially a new empty |
Once the values of[[Signifier]],[[IsLockFree1]], and[[IsLockFree2]] have been observed by any
The values of[[IsLockFree1]] and[[IsLockFree2]] are not necessarily determined by the hardware, but may also reflect implementation choices that can vary over time and between ECMAScript implementations.
There is no[[IsLockFree4]] field: 4-byte atomic operations are always lock-free.
In practice, if an atomic operation is implemented with any type of lock the operation is not lock-free. Lock-free does not imply wait-free: there is no upper bound on how many machine steps may be required to complete a lock-free atomic operation.
That an atomic access of sizen is lock-free does not imply anything about the (perceived) atomicity of non-atomic accesses of sizen, specifically, non-atomic accesses may still be performed as a sequence of several separate memory accesses. See
An
9.7.1 AgentSignifier ( )
The abstract operation AgentSignifier takes no arguments and returns an
- LetAR be the
Agent Record of thesurrounding agent . - ReturnAR.[[Signifier]].
9.7.2 AgentCanSuspend ( )
The abstract operation AgentCanSuspend takes no arguments and returns a Boolean. It performs the following steps when called:
- LetAR be the
Agent Record of thesurrounding agent . - ReturnAR.[[CanBlock]].
In some environments it may not be reasonable for a given
9.8 Agent Clusters
Anagent cluster is a maximal set of
Every
All
If different
All
All
An embedding may deactivate (stop forward progress) or activate (resume forward progress) an
The purpose of the preceding restriction is to avoid a situation where an
The implication of the restriction is that it will not be possible to share memory between
An embedding may terminate an
Each of the following specification values, and values transitively reachable from them, belong to exactly one agent cluster.
Prior to any evaluation of any ECMAScript code by any
All
An agent cluster is a specification mechanism and need not correspond to any particular artefact of an ECMAScript implementation.
9.9 Forward Progress
For an
An
Implementations must ensure that:
- every unblocked
agent with a dedicatedexecuting thread eventually makes forward progress - in a set of
agents that share anexecuting thread , oneagent eventually makes forward progress - an
agent does not cause anotheragent to become blocked except via explicit APIs that provide blocking.
This, along with the liveness guarantee in the
9.10 Processing Model of WeakRef and FinalizationRegistry Targets
9.10.1 Objectives
This specification does not make any guarantees that any object or symbol will be garbage collected. Objects or symbols which are not
The semantics of
- When
WeakRef.prototype.derefis called, the referent (ifundefined is not returned) is kept alive so that subsequent, synchronous accesses also return the same value. This list is reset when synchronous work is done using theClearKeptObjects abstract operation. - When an object or symbol which is registered with a
FinalizationRegistry becomes unreachable, a call of theFinalizationRegistry 's cleanup callback may eventually be made, after synchronous ECMAScript execution completes. TheFinalizationRegistry cleanup is performed with theCleanupFinalizationRegistry abstract operation.
Neither of these actions (
Some ECMAScript implementations include garbage collector implementations which run in the background, including when ECMAScript is idle. Letting the
9.10.2 Liveness
For some set of objects and/or symbolsS ahypothetical WeakRef-oblivious execution with respect toS is an execution whereby the abstract operation
At any point during evaluation, a set of objects and/or symbolsS is consideredlive if either of the following conditions is met:
- Any element inS is included in any
agent 's[[KeptAlive]]List . - There exists a valid future hypothetical WeakRef-oblivious execution with respect toS that observes the identity of any value inS.
Presence of an object or a symbol in a field, an internal slot, or a property does not imply that the value is live. For example if the value in question is never passed back to the program, then it cannot be observed.
This is the case for keys in a WeakMap, members of a WeakSet, as well as the[[WeakRefTarget]] and[[UnregisterToken]] fields of a
The above definition implies that, if a key in a WeakMap is not live, then its corresponding value is not necessarily live either.
9.10.3 Execution
At any time, if a set of objects and/or symbolsS is not
- For each elementvalue ofS, do
- For each
WeakRef ref such thatref.[[WeakRefTarget]] isvalue, do- Setref.[[WeakRefTarget]] to
empty .
- Setref.[[WeakRefTarget]] to
- For each
FinalizationRegistry fg such thatfg.[[Cells]] contains aRecord cell such thatcell.[[WeakRefTarget]] isvalue, do- Setcell.[[WeakRefTarget]] to
empty . - Optionally, perform
HostEnqueueFinalizationRegistryCleanupJob (fg).
- Setcell.[[WeakRefTarget]] to
- For each WeakMapmap such thatmap.[[WeakMapData]] contains a
Record r such thatr.[[Key]] isvalue, do- Setr.[[Key]] to
empty . - Setr.[[Value]] to
empty .
- Setr.[[Key]] to
- For each WeakSetset such thatset.[[WeakSetData]] containsvalue, do
- Replace the element ofset.[[WeakSetData]] whose value isvalue with an element whose value is
empty .
- Replace the element ofset.[[WeakSetData]] whose value isvalue with an element whose value is
- For each
Together with the definition of liveness, this clause prescribes optimizations that an implementation may apply regarding
It is possible to access an object without observing its identity. Optimizations such as dead variable elimination and scalar replacement on properties of non-escaping objects whose identity is not observed are allowed. These optimizations are thus allowed to observably empty
On the other hand, if an object's identity is observable, and that object is in the[[WeakRefTarget]] internal slot of a
Because calling
Implementations are not obligated to empty
If an implementation chooses a non-
9.10.4 Host Hooks
9.10.4.1 HostEnqueueFinalizationRegistryCleanupJob (finalizationRegistry )
The
LetcleanupJob be a new
- LetcleanupResult be
Completion (CleanupFinalizationRegistry (finalizationRegistry)). - IfcleanupResult is an
abrupt completion , perform anyhost-defined steps for reporting the error. - Return
unused .
An implementation of HostEnqueueFinalizationRegistryCleanupJob schedulescleanupJob to be performed at some future time, if possible. It must also conform to the requirements in
9.11 ClearKeptObjects ( )
The abstract operation ClearKeptObjects takes no arguments and returns
- LetagentRecord be the
surrounding agent 'sAgent Record . - SetagentRecord.[[KeptAlive]] to a new empty
List . - Return
unused .
9.12 AddToKeptObjects (value )
The abstract operation AddToKeptObjects takes argumentvalue (an Object or a Symbol) and returns
- LetagentRecord be the
surrounding agent 'sAgent Record . - Appendvalue toagentRecord.[[KeptAlive]].
- Return
unused .
9.13 CleanupFinalizationRegistry (finalizationRegistry )
The abstract operation CleanupFinalizationRegistry takes argumentfinalizationRegistry (a
Assert :finalizationRegistry has[[Cells]] and[[CleanupCallback]] internal slots.- Letcallback befinalizationRegistry.[[CleanupCallback]].
- WhilefinalizationRegistry.[[Cells]] contains a
Record cell such thatcell.[[WeakRefTarget]] isempty , an implementation may perform the following steps:- Choose any suchcell.
- Removecell fromfinalizationRegistry.[[Cells]].
- Perform ?
HostCallJobCallback (callback,undefined , «cell.[[HeldValue]] »).
- Return
unused .
9.14 CanBeHeldWeakly (v )
The abstract operation CanBeHeldWeakly takes argumentv (an
- Ifv
is an Object , returntrue . - Ifv
is a Symbol andKeyForSymbol (v) isundefined , returntrue . - Return
false .
A language value without
10 Ordinary and Exotic Objects Behaviours
10.1 Ordinary Object Internal Methods and Internal Slots
All
Every
In the following algorithm descriptions, assumeO is an
Each
10.1.1[[GetPrototypeOf]] ( )
The[[GetPrototypeOf]] internal method of an
- Return
OrdinaryGetPrototypeOf (O).
10.1.1.1 OrdinaryGetPrototypeOf (O )
The abstract operation OrdinaryGetPrototypeOf takes argumentO (an Object) and returns an Object or
- ReturnO.[[Prototype]].
10.1.2[[SetPrototypeOf]] (V )
The[[SetPrototypeOf]] internal method of an
- Return
OrdinarySetPrototypeOf (O,V).
10.1.2.1 OrdinarySetPrototypeOf (O,V )
The abstract operation OrdinarySetPrototypeOf takes argumentsO (an Object) andV (an Object or
- Letcurrent beO.[[Prototype]].
- If
SameValue (V,current) istrue , returntrue . - Letextensible beO.[[Extensible]].
- Ifextensible is
false , returnfalse . - Letp beV.
- Letdone be
false . - Repeat, whiledone is
false ,- Ifp is
null , then- Setdone to
true .
- Setdone to
- Else if
SameValue (p,O) istrue , then- Return
false .
- Return
- Else,
- Ifp.[[GetPrototypeOf]] is not the
ordinary object internal method defined in10.1.1 , setdone totrue . - Else, setp top.[[Prototype]].
- Ifp.[[GetPrototypeOf]] is not the
- Ifp is
- SetO.[[Prototype]] toV.
- Return
true .
The loop in step
10.1.3[[IsExtensible]] ( )
The[[IsExtensible]] internal method of an
- Return
OrdinaryIsExtensible (O).
10.1.3.1 OrdinaryIsExtensible (O )
The abstract operation OrdinaryIsExtensible takes argumentO (an Object) and returns a Boolean. It performs the following steps when called:
- ReturnO.[[Extensible]].
10.1.4[[PreventExtensions]] ( )
The[[PreventExtensions]] internal method of an
- Return
OrdinaryPreventExtensions (O).
10.1.4.1 OrdinaryPreventExtensions (O )
The abstract operation OrdinaryPreventExtensions takes argumentO (an Object) and returns
- SetO.[[Extensible]] to
false . - Return
true .
10.1.5[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of an
- Return
OrdinaryGetOwnProperty (O,P).
10.1.5.1 OrdinaryGetOwnProperty (O,P )
The abstract operation OrdinaryGetOwnProperty takes argumentsO (an Object) andP (a
- IfO does not have an own property with keyP, return
undefined . - LetD be a newly created
Property Descriptor with no fields. - LetX beO's own property whose key isP.
- IfX is a
data property , then- SetD.[[Value]] to the value ofX's[[Value]] attribute.
- SetD.[[Writable]] to the value ofX's[[Writable]] attribute.
- Else,
Assert :X is anaccessor property .- SetD.[[Get]] to the value ofX's[[Get]] attribute.
- SetD.[[Set]] to the value ofX's[[Set]] attribute.
- SetD.[[Enumerable]] to the value ofX's[[Enumerable]] attribute.
- SetD.[[Configurable]] to the value ofX's[[Configurable]] attribute.
- ReturnD.
10.1.6[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of an
- Return ?
OrdinaryDefineOwnProperty (O,P,Desc).
10.1.6.1 OrdinaryDefineOwnProperty (O,P,Desc )
The abstract operation OrdinaryDefineOwnProperty takes argumentsO (an Object),P (a
- Letcurrent be ? O.[[GetOwnProperty]](P).
- Letextensible be ?
IsExtensible (O). - Return
ValidateAndApplyPropertyDescriptor (O,P,extensible,Desc,current).
10.1.6.2 IsCompatiblePropertyDescriptor (Extensible,Desc,Current )
The abstract operation IsCompatiblePropertyDescriptor takes argumentsExtensible (a Boolean),Desc (a
- Return
ValidateAndApplyPropertyDescriptor (undefined ,"" ,Extensible,Desc,Current).
10.1.6.3 ValidateAndApplyPropertyDescriptor (O,P,extensible,Desc,current )
The abstract operation ValidateAndApplyPropertyDescriptor takes argumentsO (an Object or
Assert :IsPropertyKey (P) istrue .- Ifcurrent is
undefined , then- Ifextensible is
false , returnfalse . - IfO is
undefined , returntrue . - If
IsAccessorDescriptor (Desc) istrue , then- Create an own
accessor property namedP of objectO whose[[Get]],[[Set]],[[Enumerable]], and[[Configurable]] attributes are set to the value of the corresponding field inDesc ifDesc has that field, or to the attribute'sdefault value otherwise.
- Create an own
- Else,
- Create an own
data property namedP of objectO whose[[Value]],[[Writable]],[[Enumerable]], and[[Configurable]] attributes are set to the value of the corresponding field inDesc ifDesc has that field, or to the attribute'sdefault value otherwise.
- Create an own
- Return
true .
- Ifextensible is
Assert :current is afully populated Property Descriptor .- IfDesc does not have any fields, return
true . - Ifcurrent.[[Configurable]] is
false , then- IfDesc has a[[Configurable]] field andDesc.[[Configurable]] is
true , returnfalse . - IfDesc has an[[Enumerable]] field andDesc.[[Enumerable]] is notcurrent.[[Enumerable]], return
false . - If
IsGenericDescriptor (Desc) isfalse andIsAccessorDescriptor (Desc) is notIsAccessorDescriptor (current), returnfalse . - If
IsAccessorDescriptor (current) istrue , then - Else ifcurrent.[[Writable]] is
false , then- IfDesc has a[[Writable]] field andDesc.[[Writable]] is
true , returnfalse . - IfDesc has a[[Value]] field and
SameValue (Desc.[[Value]],current.[[Value]]) isfalse , returnfalse .
- IfDesc has a[[Writable]] field andDesc.[[Writable]] is
- IfDesc has a[[Configurable]] field andDesc.[[Configurable]] is
- IfO is not
undefined , then- If
IsDataDescriptor (current) istrue andIsAccessorDescriptor (Desc) istrue , then- IfDesc has a[[Configurable]] field, letconfigurable beDesc.[[Configurable]]; else letconfigurable becurrent.[[Configurable]].
- IfDesc has a[[Enumerable]] field, letenumerable beDesc.[[Enumerable]]; else letenumerable becurrent.[[Enumerable]].
- Replace the property namedP of objectO with an
accessor property whose[[Configurable]] and[[Enumerable]] attributes are set toconfigurable andenumerable, respectively, and whose[[Get]] and[[Set]] attributes are set to the value of the corresponding field inDesc ifDesc has that field, or to the attribute'sdefault value otherwise.
- Else if
IsAccessorDescriptor (current) istrue andIsDataDescriptor (Desc) istrue , then- IfDesc has a[[Configurable]] field, letconfigurable beDesc.[[Configurable]]; else letconfigurable becurrent.[[Configurable]].
- IfDesc has a[[Enumerable]] field, letenumerable beDesc.[[Enumerable]]; else letenumerable becurrent.[[Enumerable]].
- Replace the property namedP of objectO with a
data property whose[[Configurable]] and[[Enumerable]] attributes are set toconfigurable andenumerable, respectively, and whose[[Value]] and[[Writable]] attributes are set to the value of the corresponding field inDesc ifDesc has that field, or to the attribute'sdefault value otherwise.
- Else,
- For each field ofDesc, set the corresponding attribute of the property namedP of objectO to the value of the field.
- If
- Return
true .
10.1.7[[HasProperty]] (P )
The[[HasProperty]] internal method of an
- Return ?
OrdinaryHasProperty (O,P).
10.1.7.1 OrdinaryHasProperty (O,P )
The abstract operation OrdinaryHasProperty takes argumentsO (an Object) andP (a
- LethasOwn be ? O.[[GetOwnProperty]](P).
- IfhasOwn is not
undefined , returntrue . - Letparent be ? O.[[GetPrototypeOf]]().
- Ifparent is not
null , then- Return ? parent.[[HasProperty]](P).
- Return
false .
10.1.8[[Get]] (P,Receiver )
The[[Get]] internal method of an
- Return ?
OrdinaryGet (O,P,Receiver).
10.1.8.1 OrdinaryGet (O,P,Receiver )
The abstract operation OrdinaryGet takes argumentsO (an Object),P (a
- Letdesc be ? O.[[GetOwnProperty]](P).
- Ifdesc is
undefined , then- Letparent be ? O.[[GetPrototypeOf]]().
- Ifparent is
null , returnundefined . - Return ? parent.[[Get]](P,Receiver).
- If
IsDataDescriptor (desc) istrue , returndesc.[[Value]]. Assert :IsAccessorDescriptor (desc) istrue .- Letgetter bedesc.[[Get]].
- Ifgetter is
undefined , returnundefined . - Return ?
Call (getter,Receiver).
10.1.9[[Set]] (P,V,Receiver )
The[[Set]] internal method of an
- Return ?
OrdinarySet (O,P,V,Receiver).
10.1.9.1 OrdinarySet (O,P,V,Receiver )
The abstract operation OrdinarySet takes argumentsO (an Object),P (a
- LetownDesc be ? O.[[GetOwnProperty]](P).
- Return ?
OrdinarySetWithOwnDescriptor (O,P,V,Receiver,ownDesc).
10.1.9.2 OrdinarySetWithOwnDescriptor (O,P,V,Receiver,ownDesc )
The abstract operation OrdinarySetWithOwnDescriptor takes argumentsO (an Object),P (a
- IfownDesc is
undefined , then- Letparent be ? O.[[GetPrototypeOf]]().
- Ifparent is not
null , then- Return ? parent.[[Set]](P,V,Receiver).
- Else,
- SetownDesc to the PropertyDescriptor {[[Value]]:
undefined ,[[Writable]]:true ,[[Enumerable]]:true ,[[Configurable]]:true }.
- SetownDesc to the PropertyDescriptor {[[Value]]:
- If
IsDataDescriptor (ownDesc) istrue , then- IfownDesc.[[Writable]] is
false , returnfalse . - IfReceiver
is not an Object , returnfalse . - LetexistingDescriptor be ? Receiver.[[GetOwnProperty]](P).
- IfexistingDescriptor is not
undefined , then- If
IsAccessorDescriptor (existingDescriptor) istrue , returnfalse . - IfexistingDescriptor.[[Writable]] is
false , returnfalse . - LetvalueDesc be the PropertyDescriptor {[[Value]]:V }.
- Return ? Receiver.[[DefineOwnProperty]](P,valueDesc).
- If
- Else,
Assert :Receiver does not currently have a propertyP.- Return ?
CreateDataProperty (Receiver,P,V).
- IfownDesc.[[Writable]] is
Assert :IsAccessorDescriptor (ownDesc) istrue .- Letsetter beownDesc.[[Set]].
- Ifsetter is
undefined , returnfalse . - Perform ?
Call (setter,Receiver, «V »). - Return
true .
10.1.10[[Delete]] (P )
The[[Delete]] internal method of an
- Return ?
OrdinaryDelete (O,P).
10.1.10.1 OrdinaryDelete (O,P )
The abstract operation OrdinaryDelete takes argumentsO (an Object) andP (a
- Letdesc be ? O.[[GetOwnProperty]](P).
- Ifdesc is
undefined , returntrue . - Ifdesc.[[Configurable]] is
true , then- Remove the own property with nameP fromO.
- Return
true .
- Return
false .
10.1.11[[OwnPropertyKeys]] ( )
The[[OwnPropertyKeys]] internal method of an
- Return
OrdinaryOwnPropertyKeys (O).
10.1.11.1 OrdinaryOwnPropertyKeys (O )
The abstract operation OrdinaryOwnPropertyKeys takes argumentO (an Object) and returns a
- Letkeys be a new empty
List . - For each own
property key P ofO such thatP is anarray index , in ascending numeric index order, do- AppendP tokeys.
- For each own
property key P ofO such thatPis a String andP is not anarray index , in ascending chronological order of property creation, do- AppendP tokeys.
- For each own
property key P ofO such thatPis a Symbol , in ascending chronological order of property creation, do- AppendP tokeys.
- Returnkeys.
10.1.12 OrdinaryObjectCreate (proto [ ,additionalInternalSlotsList ] )
The abstract operation OrdinaryObjectCreate takes argumentproto (an Object or
- LetinternalSlotsList be «[[Prototype]],[[Extensible]] ».
- IfadditionalInternalSlotsList is present, setinternalSlotsList to the
list-concatenation ofinternalSlotsList andadditionalInternalSlotsList. - LetO be
MakeBasicObject (internalSlotsList). - SetO.[[Prototype]] toproto.
- ReturnO.
Although OrdinaryObjectCreate does little more than call
10.1.13 OrdinaryCreateFromConstructor (constructor,intrinsicDefaultProto [ ,internalSlotsList ] )
The abstract operation OrdinaryCreateFromConstructor takes argumentsconstructor (a
Assert :intrinsicDefaultProto is this specification's name of an intrinsic object. The corresponding object must be an intrinsic that is intended to be used as the[[Prototype]] value of an object.- Letproto be ?
GetPrototypeFromConstructor (constructor,intrinsicDefaultProto). - IfinternalSlotsList is present, letslotsList beinternalSlotsList.
- Else, letslotsList be a new empty
List . - Return
OrdinaryObjectCreate (proto,slotsList).
10.1.14 GetPrototypeFromConstructor (constructor,intrinsicDefaultProto )
The abstract operation GetPrototypeFromConstructor takes argumentsconstructor (a
Assert :intrinsicDefaultProto is this specification's name of an intrinsic object. The corresponding object must be an intrinsic that is intended to be used as the[[Prototype]] value of an object.- Letproto be ?
Get (constructor,"prototype" ). - Ifproto
is not an Object , then- Letrealm be ?
GetFunctionRealm (constructor). - Setproto torealm's intrinsic object namedintrinsicDefaultProto.
- Letrealm be ?
- Returnproto.
Ifconstructor does not supply a[[Prototype]] value, the default value that is used is obtained from the
10.1.15 RequireInternalSlot (O,internalSlot )
The abstract operation RequireInternalSlot takes argumentsO (an
- IfO
is not an Object , throw aTypeError exception. - IfO does not have aninternalSlot internal slot, throw a
TypeError exception. - Return
unused .
10.2 ECMAScript Function Objects
ECMAScript
In addition to[[Extensible]] and[[Prototype]], ECMAScript
| Internal Slot | Type | Description |
|---|---|---|
| [[Environment]] | an | The |
| [[PrivateEnvironment]] | a | The |
| [[FormalParameters]] | a | The root parse node of the source text that defines the function's formal parameter list. |
| [[ECMAScriptCode]] | a | The root parse node of the source text that defines the function's body. |
| [[ConstructorKind]] | Whether or not the function is a derived class | |
| [[Realm]] | a | The |
| [[ScriptOrModule]] | a | The script or module in which the function was created. |
| [[ThisMode]] | Defines howthis references are interpreted within the formal parameters and code body of the function.this refers to the | |
| [[Strict]] | a Boolean | |
| [[HomeObject]] | an Object | If the function usessuper, this is the object whose[[GetPrototypeOf]] provides the object wheresuper property lookups begin. |
| [[SourceText]] | a sequence of Unicode code points | The |
| [[Fields]] | a | If the function is a class, this is a list of |
| [[PrivateMethods]] | a | If the function is a class, this is a list representing the non-static private methods and accessors of the class. |
| [[ClassFieldInitializerName]] | a String, a Symbol, a | If the function is created as the initializer of a class field, the name to use for |
| [[IsClassConstructor]] | a Boolean | Indicates whether the function is a class |
All ECMAScript
10.2.1[[Call]] (thisArgument,argumentsList )
The[[Call]] internal method of an ECMAScript
- LetcallerContext be the
running execution context . - LetcalleeContext be
PrepareForOrdinaryCall (F,undefined ). Assert :calleeContext is now therunning execution context .- IfF.[[IsClassConstructor]] is
true , then- Leterror be a newly created
TypeError object. - NOTE:error is created incalleeContext withF's associated
Realm Record . - RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Return
ThrowCompletion (error).
- Leterror be a newly created
- Perform
OrdinaryCallBindThis (F,calleeContext,thisArgument). - Letresult be
Completion (OrdinaryCallEvaluateBody (F,argumentsList)). - RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Ifresult is a
return completion , returnresult.[[Value]]. ReturnIfAbrupt (result).- Return
undefined .
WhencalleeContext is removed from the
10.2.1.1 PrepareForOrdinaryCall (F,newTarget )
The abstract operation PrepareForOrdinaryCall takes argumentsF (an ECMAScript
- LetcallerContext be the
running execution context . - LetcalleeContext be a new
ECMAScript code execution context . - Set the Function ofcalleeContext toF.
- LetcalleeRealm beF.[[Realm]].
- Set the
Realm ofcalleeContext tocalleeRealm. - Set the ScriptOrModule ofcalleeContext toF.[[ScriptOrModule]].
- LetlocalEnv be
NewFunctionEnvironment (F,newTarget). - Set the LexicalEnvironment ofcalleeContext tolocalEnv.
- Set the VariableEnvironment ofcalleeContext tolocalEnv.
- Set the PrivateEnvironment ofcalleeContext toF.[[PrivateEnvironment]].
- IfcallerContext is not already suspended, suspendcallerContext.
- PushcalleeContext onto the
execution context stack ;calleeContext is now therunning execution context . - NOTE: Any exception objects produced after this point are associated withcalleeRealm.
- ReturncalleeContext.
10.2.1.2 OrdinaryCallBindThis (F,calleeContext,thisArgument )
The abstract operation OrdinaryCallBindThis takes argumentsF (an ECMAScript
- LetthisMode beF.[[ThisMode]].
- IfthisMode is
lexical , returnunused . - LetcalleeRealm beF.[[Realm]].
- LetlocalEnv be the LexicalEnvironment ofcalleeContext.
- IfthisMode is
strict , then- LetthisValue bethisArgument.
- Else,
- IfthisArgument is either
undefined ornull , then- LetglobalEnv becalleeRealm.[[GlobalEnv]].
Assert :globalEnv is aGlobal Environment Record .- LetthisValue beglobalEnv.[[GlobalThisValue]].
- Else,
- IfthisArgument is either
Assert :localEnv is aFunction Environment Record .Assert : The next step never returns anabrupt completion becauselocalEnv.[[ThisBindingStatus]] is notinitialized .- Perform ! localEnv.BindThisValue(thisValue).
- Return
unused .
10.2.1.3 Runtime Semantics: EvaluateBody
The
- Return ?
EvaluateFunctionBody ofFunctionBody with argumentsfunctionObject andargumentsList.
- Return ?
EvaluateConciseBody ofConciseBody with argumentsfunctionObject andargumentsList.
- Return ?
EvaluateGeneratorBody ofGeneratorBody with argumentsfunctionObject andargumentsList.
- Return ?
EvaluateAsyncGeneratorBody ofAsyncGeneratorBody with argumentsfunctionObject andargumentsList.
- Return ?
EvaluateAsyncFunctionBody ofAsyncFunctionBody with argumentsfunctionObject andargumentsList.
- Return ?
EvaluateAsyncConciseBody ofAsyncConciseBody with argumentsfunctionObject andargumentsList.
Assert :argumentsList is empty.Assert :functionObject.[[ClassFieldInitializerName]] is notempty .- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Letvalue be ?
NamedEvaluation ofInitializer with argumentfunctionObject.[[ClassFieldInitializerName]].
- Letvalue be ?
- Else,
- Letrhs be ?
Evaluation ofAssignmentExpression . - Letvalue be ?
GetValue (rhs).
- Letrhs be ?
- Return
Completion Record {[[Type]]:return ,[[Value]]:value,[[Target]]:empty }.
Even though field initializers constitute a function boundary, calling
Assert :argumentsList is empty.- Return ?
EvaluateClassStaticBlockBody ofClassStaticBlockBody with argumentfunctionObject.
10.2.1.4 OrdinaryCallEvaluateBody (F,argumentsList )
The abstract operation OrdinaryCallEvaluateBody takes argumentsF (an ECMAScript
- Return ?
EvaluateBody ofF.[[ECMAScriptCode]] with argumentsF andargumentsList.
10.2.2[[Construct]] (argumentsList,newTarget )
The[[Construct]] internal method of an ECMAScript
- LetcallerContext be the
running execution context . - Letkind beF.[[ConstructorKind]].
- Ifkind is
base , then- LetthisArgument be ?
OrdinaryCreateFromConstructor (newTarget,"%Object.prototype%" ).
- LetthisArgument be ?
- LetcalleeContext be
PrepareForOrdinaryCall (F,newTarget). Assert :calleeContext is now therunning execution context .- Ifkind is
base , then- Perform
OrdinaryCallBindThis (F,calleeContext,thisArgument). - LetinitializeResult be
Completion (InitializeInstanceElements (thisArgument,F)). - IfinitializeResult is an
abrupt completion , then- RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Return ? initializeResult.
- RemovecalleeContext from the
- Perform
- LetconstructorEnv be the LexicalEnvironment ofcalleeContext.
- Letresult be
Completion (OrdinaryCallEvaluateBody (F,argumentsList)). - RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Ifresult is a
return completion , then- Ifresult.[[Value]]
is an Object , returnresult.[[Value]]. - Ifkind is
base , returnthisArgument. - Ifresult.[[Value]] is not
undefined , throw aTypeError exception.
- Ifresult.[[Value]]
- Else,
ReturnIfAbrupt (result).
- LetthisBinding be ? constructorEnv.GetThisBinding().
Assert :thisBindingis an Object .- ReturnthisBinding.
10.2.3 OrdinaryFunctionCreate (functionPrototype,sourceText,ParameterList,Body,thisMode,env,privateEnv )
The abstract operation OrdinaryFunctionCreate takes argumentsfunctionPrototype (an Object),sourceText (a sequence of Unicode code points),ParameterList (a
- LetinternalSlotsList be the internal slots listed in
Table 30 . - LetF be
OrdinaryObjectCreate (functionPrototype,internalSlotsList). - SetF.[[Call]] to the definition specified in
10.2.1 . - SetF.[[SourceText]] tosourceText.
- SetF.[[FormalParameters]] toParameterList.
- SetF.[[ECMAScriptCode]] toBody.
- If the
source text matched by Body isstrict mode code , letStrict betrue ; else letStrict befalse . - SetF.[[Strict]] toStrict.
- IfthisMode is
lexical-this , setF.[[ThisMode]] tolexical . - Else ifStrict is
true , setF.[[ThisMode]] tostrict . - Else, setF.[[ThisMode]] to
global . - SetF.[[IsClassConstructor]] to
false . - SetF.[[Environment]] toenv.
- SetF.[[PrivateEnvironment]] toprivateEnv.
- SetF.[[ScriptOrModule]] to
GetActiveScriptOrModule (). - SetF.[[Realm]] to
the current Realm Record . - SetF.[[HomeObject]] to
undefined . - SetF.[[Fields]] to a new empty
List . - SetF.[[PrivateMethods]] to a new empty
List . - SetF.[[ClassFieldInitializerName]] to
empty . - Letlen be the
ExpectedArgumentCount ofParameterList. - Perform
SetFunctionLength (F,len). - ReturnF.
10.2.4 AddRestrictedFunctionProperties (F,realm )
The abstract operation AddRestrictedFunctionProperties takes argumentsF (a
Assert :realm.[[Intrinsics]].[[%ThrowTypeError% ]] exists and has been initialized.- Letthrower berealm.[[Intrinsics]].[[
%ThrowTypeError% ]]. - Perform !
DefinePropertyOrThrow (F,"caller" , PropertyDescriptor {[[Get]]:thrower,[[Set]]:thrower,[[Enumerable]]:false ,[[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (F,"arguments" , PropertyDescriptor {[[Get]]:thrower,[[Set]]:thrower,[[Enumerable]]:false ,[[Configurable]]:true }). - Return
unused .
10.2.4.1 %ThrowTypeError% ( )
This function is the%ThrowTypeError% intrinsic object.
It is an anonymous built-in
It performs the following steps when called:
- Throw a
TypeError exception.
The value of the[[Extensible]] internal slot of this function is
The
The
10.2.5 MakeConstructor (F [ ,writablePrototype [ ,prototype ] ] )
The abstract operation MakeConstructor takes argumentF (an ECMAScript
- IfF is an ECMAScript
function object , thenAssert :IsConstructor (F) isfalse .Assert :F is an extensible object that does not have a"prototype" own property.- SetF.[[Construct]] to the definition specified in
10.2.2 .
- Else,
- SetF.[[Construct]] to the definition specified in
10.3.2 .
- SetF.[[Construct]] to the definition specified in
- SetF.[[ConstructorKind]] to
base . - IfwritablePrototype is not present, setwritablePrototype to
true . - Ifprototype is not present, then
- Setprototype to
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
DefinePropertyOrThrow (prototype,"constructor" , PropertyDescriptor {[[Value]]:F,[[Writable]]:writablePrototype,[[Enumerable]]:false ,[[Configurable]]:true }).
- Setprototype to
- Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:writablePrototype,[[Enumerable]]:false ,[[Configurable]]:false }). - Return
unused .
10.2.6 MakeClassConstructor (F )
The abstract operation MakeClassConstructor takes argumentF (an ECMAScript
Assert :F.[[IsClassConstructor]] isfalse .- SetF.[[IsClassConstructor]] to
true . - Return
unused .
10.2.7 MakeMethod (F,homeObject )
The abstract operation MakeMethod takes argumentsF (an ECMAScript
- SetF.[[HomeObject]] tohomeObject.
- Return
unused .
10.2.8 DefineMethodProperty (homeObject,key,closure,enumerable )
The abstract operation DefineMethodProperty takes argumentshomeObject (an Object),key (a
Assert :homeObject is an ordinary, extensible object.- Ifkey is a
Private Name , then- Return
PrivateElement {[[Key]]:key,[[Kind]]:method ,[[Value]]:closure }.
- Return
- Else,
- Letdesc be the PropertyDescriptor {[[Value]]:closure,[[Writable]]:
true ,[[Enumerable]]:enumerable,[[Configurable]]:true }. - Perform ?
DefinePropertyOrThrow (homeObject,key,desc). - NOTE:
DefinePropertyOrThrow only returns anabrupt completion when attempting to define a class static method whosekey is"prototype" . - Return
unused .
- Letdesc be the PropertyDescriptor {[[Value]]:closure,[[Writable]]:
10.2.9 SetFunctionName (F,name [ ,prefix ] )
The abstract operation SetFunctionName takes argumentsF (a
Assert :F is an extensible object that does not have a"name" own property.- Ifname
is a Symbol , then- Letdescription bename's[[Description]] value.
- Ifdescription is
undefined , setname to the empty String. - Else, setname to the
string-concatenation of"[" ,description, and"]" .
- Else ifname is a
Private Name , then- Setname toname.[[Description]].
- IfF has an[[InitialName]] internal slot, then
- SetF.[[InitialName]] toname.
- Ifprefix is present, then
- Setname to the
string-concatenation ofprefix, the code unit 0x0020 (SPACE), andname. - IfF has an[[InitialName]] internal slot, then
- Optionally, setF.[[InitialName]] toname.
- Setname to the
- Perform !
DefinePropertyOrThrow (F,"name" , PropertyDescriptor {[[Value]]:name,[[Writable]]:false ,[[Enumerable]]:false ,[[Configurable]]:true }). - Return
unused .
10.2.10 SetFunctionLength (F,length )
The abstract operation SetFunctionLength takes argumentsF (a
Assert :F is an extensible object that does not have a"length" own property.- Perform !
DefinePropertyOrThrow (F,"length" , PropertyDescriptor {[[Value]]:𝔽 (length),[[Writable]]:false ,[[Enumerable]]:false ,[[Configurable]]:true }). - Return
unused .
10.2.11 FunctionDeclarationInstantiation (func,argumentsList )
The abstract operation FunctionDeclarationInstantiation takes argumentsfunc (an ECMAScript
When an
It performs the following steps when called:
- LetcalleeContext be the
running execution context . - Letcode befunc.[[ECMAScriptCode]].
- Letstrict befunc.[[Strict]].
- Letformals befunc.[[FormalParameters]].
- LetparameterNames be the
BoundNames offormals. - IfparameterNames has any duplicate entries, lethasDuplicates be
true . Otherwise, lethasDuplicates befalse . - LetsimpleParameterList be
IsSimpleParameterList offormals. - LethasParameterExpressions be
ContainsExpression offormals. - LetvarNames be the
VarDeclaredNames ofcode. - LetvarDeclarations be the
VarScopedDeclarations ofcode. - LetlexicalNames be the
LexicallyDeclaredNames ofcode. - LetfunctionNames be a new empty
List . - LetfunctionsToInitialize be a new empty
List . - For each elementd ofvarDeclarations, in reverse
List order, do- Ifd is neither a
VariableDeclaration nor aForBinding nor aBindingIdentifier , thenAssert :d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- Letfn be the sole element of the
BoundNames ofd. - IffunctionNames does not containfn, then
- Insertfn as the first element offunctionNames.
- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Insertd as the first element offunctionsToInitialize.
- Ifd is neither a
- LetargumentsObjectNeeded be
true . - Iffunc.[[ThisMode]] is
lexical , then- NOTE: Arrow functions never have an arguments object.
- SetargumentsObjectNeeded to
false .
- Else ifparameterNames contains
"arguments" , then- SetargumentsObjectNeeded to
false .
- SetargumentsObjectNeeded to
- Else ifhasParameterExpressions is
false , then- IffunctionNames contains
"arguments" orlexicalNames contains"arguments" , then- SetargumentsObjectNeeded to
false .
- SetargumentsObjectNeeded to
- IffunctionNames contains
- Ifstrict is
true orhasParameterExpressions isfalse , then- NOTE: Only a single
Environment Record is needed for the parameters, since calls toevalinstrict mode code cannot create new bindings which are visible outside of theeval. - Letenv be the LexicalEnvironment ofcalleeContext.
- NOTE: Only a single
- Else,
- NOTE: A separate
Environment Record is needed to ensure that bindings created bydirect eval calls in the formal parameter list are outside the environment where parameters are declared. - LetcalleeEnv be the LexicalEnvironment ofcalleeContext.
- Letenv be
NewDeclarativeEnvironment (calleeEnv). Assert : The VariableEnvironment ofcalleeContext iscalleeEnv.- Set the LexicalEnvironment ofcalleeContext toenv.
- NOTE: A separate
- For each StringparamName ofparameterNames, do
- LetalreadyDeclared be ! env.HasBinding(paramName).
- NOTE:
Early errors ensure that duplicate parameter names can only occur innon-strict functions that do not have parameter default values or rest parameters. - IfalreadyDeclared is
false , then- Perform ! env.CreateMutableBinding(paramName,
false ). - IfhasDuplicates is
true , then- Perform ! env.InitializeBinding(paramName,
undefined ).
- Perform ! env.InitializeBinding(paramName,
- Perform ! env.CreateMutableBinding(paramName,
- IfargumentsObjectNeeded is
true , then- Ifstrict is
true orsimpleParameterList isfalse , then- Letao be
CreateUnmappedArgumentsObject (argumentsList).
- Letao be
- Else,
- NOTE: A mapped argument object is only provided for
non-strict functions that don't have a rest parameter, any parameter default value initializers, or any destructured parameters. - Letao be
CreateMappedArgumentsObject (func,formals,argumentsList,env).
- NOTE: A mapped argument object is only provided for
- Ifstrict is
true , then- Perform ! env.CreateImmutableBinding(
"arguments" ,false ). - NOTE: In
strict mode code early errors prevent attempting to assign to this binding, so its mutability is not observable.
- Perform ! env.CreateImmutableBinding(
- Else,
- Perform ! env.CreateMutableBinding(
"arguments" ,false ).
- Perform ! env.CreateMutableBinding(
- Perform ! env.InitializeBinding(
"arguments" ,ao). - LetparameterBindings be the
list-concatenation ofparameterNames and «"arguments" ».
- Ifstrict is
- Else,
- LetparameterBindings beparameterNames.
- LetiteratorRecord be
CreateListIteratorRecord (argumentsList). - IfhasDuplicates is
true , then- Perform ?
IteratorBindingInitialization offormals with argumentsiteratorRecord andundefined .
- Perform ?
- Else,
- Perform ?
IteratorBindingInitialization offormals with argumentsiteratorRecord andenv.
- Perform ?
- IfhasParameterExpressions is
false , then- NOTE: Only a single
Environment Record is needed for the parameters and top-level vars. - LetinstantiatedVarNames be a copy of the
List parameterBindings. - For each elementn ofvarNames, do
- IfinstantiatedVarNames does not containn, then
- Appendn toinstantiatedVarNames.
- Perform ! env.CreateMutableBinding(n,
false ). - Perform ! env.InitializeBinding(n,
undefined ).
- IfinstantiatedVarNames does not containn, then
- LetvarEnv beenv.
- NOTE: Only a single
- Else,
- NOTE: A separate
Environment Record is needed to ensure that closures created by expressions in the formal parameter list do not have visibility of declarations in the function body. - LetvarEnv be
NewDeclarativeEnvironment (env). - Set the VariableEnvironment ofcalleeContext tovarEnv.
- LetinstantiatedVarNames be a new empty
List . - For each elementn ofvarNames, do
- IfinstantiatedVarNames does not containn, then
- Appendn toinstantiatedVarNames.
- Perform ! varEnv.CreateMutableBinding(n,
false ). - IfparameterBindings does not containn, or iffunctionNames containsn, then
- LetinitialValue be
undefined .
- LetinitialValue be
- Else,
- LetinitialValue be ! env.GetBindingValue(n,
false ).
- LetinitialValue be ! env.GetBindingValue(n,
- Perform ! varEnv.InitializeBinding(n,initialValue).
- NOTE: A var with the same name as a formal parameter initially has the same value as the corresponding initialized parameter.
- IfinstantiatedVarNames does not containn, then
- NOTE: A separate
- NOTE: Annex
B.3.2.1 adds additional steps at this point. - Ifstrict is
false , then- LetlexEnv be
NewDeclarativeEnvironment (varEnv). - NOTE:
Non-strict functions use a separateEnvironment Record for top-level lexical declarations so that adirect eval can determine whether any var scoped declarations introduced by the eval code conflict with pre-existing top-level lexically scoped declarations. This is not needed forstrict functions because a strictdirect eval always places all declarations into a newEnvironment Record .
- LetlexEnv be
- Else,
- LetlexEnv bevarEnv.
- Set the LexicalEnvironment ofcalleeContext tolexEnv.
- LetlexDeclarations be the
LexicallyScopedDeclarations ofcode. - For each elementd oflexDeclarations, do
- NOTE: A lexically declared name cannot be the same as a function/generator declaration, formal parameter, or a var name. Lexically declared names are only instantiated here but not initialized.
- For each elementdn of the
BoundNames ofd, do- If
IsConstantDeclaration ofd istrue , then- Perform ! lexEnv.CreateImmutableBinding(dn,
true ).
- Perform ! lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform ! lexEnv.CreateMutableBinding(dn,
false ).
- Perform ! lexEnv.CreateMutableBinding(dn,
- If
- LetprivateEnv be the PrivateEnvironment ofcalleeContext.
- For each
Parse Node f offunctionsToInitialize, do- Letfn be the sole element of the
BoundNames off. - Letfo be
InstantiateFunctionObject off with argumentslexEnv andprivateEnv. - Perform ! varEnv.SetMutableBinding(fn,fo,
false ).
- Letfn be the sole element of the
- Return
unused .
10.3 Built-in Function Objects
A built-in
In addition to the internal slots required of every
- [[Realm]], a
Realm Record that represents therealm in which the function was created. - [[InitialName]], a String that is the initial name of the function. It is used by
20.2.3.5 .
The initial value of a built-in
A built-in
A built-in
An implementation may provide additional built-in
10.3.1[[Call]] (thisArgument,argumentsList )
The[[Call]] internal method of a built-in
- Return ?
BuiltinCallOrConstruct (F,thisArgument,argumentsList,undefined ).
10.3.2[[Construct]] (argumentsList,newTarget )
The[[Construct]] internal method of a built-in
- Return ?
BuiltinCallOrConstruct (F,uninitialized ,argumentsList,newTarget).
10.3.3 BuiltinCallOrConstruct (F,thisArgument,argumentsList,newTarget )
The abstract operation BuiltinCallOrConstruct takes argumentsF (a built-in
- LetcallerContext be the
running execution context . - IfcallerContext is not already suspended, suspendcallerContext.
- LetcalleeContext be a new
execution context . - Set the Function ofcalleeContext toF.
- LetcalleeRealm beF.[[Realm]].
- Set the
Realm ofcalleeContext tocalleeRealm. - Set the ScriptOrModule ofcalleeContext to
null . - Perform any necessary
implementation-defined initialization ofcalleeContext. - PushcalleeContext onto the
execution context stack ;calleeContext is now therunning execution context . - Letresult be the
Completion Record that isthe result of evaluatingF in a manner that conforms to the specification ofF. IfthisArgument isuninitialized , thethis value is uninitialized; otherwise,thisArgument provides thethis value.argumentsList provides the named parameters.newTarget provides the NewTarget value. - NOTE: IfF is defined in this document, “the specification ofF” is the behaviour specified for it via algorithm steps or other means.
- RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Return ? result.
WhencalleeContext is removed from the
10.3.4 CreateBuiltinFunction (behaviour,length,name,additionalInternalSlotsList [ ,realm [ ,prototype [ ,prefix ] ] ] )
The abstract operation CreateBuiltinFunction takes argumentsbehaviour (an
- Ifrealm is not present, setrealm to
the current Realm Record . - Ifprototype is not present, setprototype torealm.[[Intrinsics]].[[
%Function.prototype% ]]. - LetinternalSlotsList be a
List containing the names of all the internal slots that10.3 requires for the built-infunction object that is about to be created. - Append tointernalSlotsList the elements ofadditionalInternalSlotsList.
- Letfunc be a new built-in
function object that, when called, performs the action described bybehaviour using the provided arguments as the values of the corresponding parameters specified bybehaviour. The newfunction object has internal slots whose names are the elements ofinternalSlotsList, and an[[InitialName]] internal slot. - Setfunc.[[Prototype]] toprototype.
- Setfunc.[[Extensible]] to
true . - Setfunc.[[Realm]] torealm.
- Setfunc.[[InitialName]] to
null . - Perform
SetFunctionLength (func,length). - Ifprefix is not present, then
- Perform
SetFunctionName (func,name).
- Perform
- Else,
- Perform
SetFunctionName (func,name,prefix).
- Perform
- Returnfunc.
Each built-in function defined in this specification is created by calling the CreateBuiltinFunction abstract operation.
10.4 Built-in Exotic Object Internal Methods and Slots
This specification defines several kinds of built-in
10.4.1 Bound Function Exotic Objects
A
An object is abound function exotic object if its[[Call]] and (if applicable)[[Construct]] internal methods use the following implementations, and its other essential internal methods use the definitions found in
| Internal Slot | Type | Description |
|---|---|---|
| [[BoundTargetFunction]] | a callable Object | The wrapped |
| [[BoundThis]] | an | The value that is always passed as the |
| [[BoundArguments]] | a | A list of values whose elements are used as the first arguments to any call to the wrapped function. |
10.4.1.1[[Call]] (thisArgument,argumentsList )
The[[Call]] internal method of a
- Lettarget beF.[[BoundTargetFunction]].
- LetboundThis beF.[[BoundThis]].
- LetboundArgs beF.[[BoundArguments]].
- Letargs be the
list-concatenation ofboundArgs andargumentsList. - Return ?
Call (target,boundThis,args).
10.4.1.2[[Construct]] (argumentsList,newTarget )
The[[Construct]] internal method of a
- Lettarget beF.[[BoundTargetFunction]].
Assert :IsConstructor (target) istrue .- LetboundArgs beF.[[BoundArguments]].
- Letargs be the
list-concatenation ofboundArgs andargumentsList. - If
SameValue (F,newTarget) istrue , setnewTarget totarget. - Return ?
Construct (target,args,newTarget).
10.4.1.3 BoundFunctionCreate (targetFunction,boundThis,boundArgs )
The abstract operation BoundFunctionCreate takes argumentstargetFunction (a
- Letproto be ? targetFunction.[[GetPrototypeOf]]().
- LetinternalSlotsList be the
list-concatenation of «[[Prototype]],[[Extensible]] » and the internal slots listed inTable 31 . - Letobj be
MakeBasicObject (internalSlotsList). - Setobj.[[Prototype]] toproto.
- Setobj.[[Call]] as described in
10.4.1.1 . - If
IsConstructor (targetFunction) istrue , then- Setobj.[[Construct]] as described in
10.4.1.2 .
- Setobj.[[Construct]] as described in
- Setobj.[[BoundTargetFunction]] totargetFunction.
- Setobj.[[BoundThis]] toboundThis.
- Setobj.[[BoundArguments]] toboundArgs.
- Returnobj.
10.4.2 Array Exotic Objects
An Array is an
An object is anArray exotic object (or simply, an Array) if its[[DefineOwnProperty]] internal method uses the following implementation, and its other essential internal methods use the definitions found in
10.4.2.1[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of an
- IfP is
"length" , then- Return ?
ArraySetLength (A,Desc).
- Return ?
- Else ifP is an
array index , then- LetlengthDesc be
OrdinaryGetOwnProperty (A,"length" ). Assert :IsDataDescriptor (lengthDesc) istrue .Assert :lengthDesc.[[Configurable]] isfalse .- Letlength belengthDesc.[[Value]].
Assert :length is a non-negativeintegral Number .- Letindex be !
ToUint32 (P). - Ifindex ≥length andlengthDesc.[[Writable]] is
false , returnfalse . - Letsucceeded be !
OrdinaryDefineOwnProperty (A,P,Desc). - Ifsucceeded is
false , returnfalse . - Ifindex ≥length, then
- SetlengthDesc.[[Value]] toindex +
1 𝔽. - Setsucceeded to !
OrdinaryDefineOwnProperty (A,"length" ,lengthDesc). Assert :succeeded istrue .
- SetlengthDesc.[[Value]] toindex +
- Return
true .
- LetlengthDesc be
- Return ?
OrdinaryDefineOwnProperty (A,P,Desc).
10.4.2.2 ArrayCreate (length [ ,proto ] )
The abstract operation ArrayCreate takes argumentlength (a non-negative
- Iflength > 232 - 1, throw a
RangeError exception. - Ifproto is not present, setproto to
%Array.prototype% . - LetA be
MakeBasicObject («[[Prototype]],[[Extensible]] »). - SetA.[[Prototype]] toproto.
- SetA.[[DefineOwnProperty]] as specified in
10.4.2.1 . - Perform !
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor {[[Value]]:𝔽 (length),[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnA.
10.4.2.3 ArraySpeciesCreate (originalArray,length )
The abstract operation ArraySpeciesCreate takes argumentsoriginalArray (an Object) andlength (a non-negative
- LetisArray be ?
IsArray (originalArray). - IfisArray is
false , return ?ArrayCreate (length). - LetC be ?
Get (originalArray,"constructor" ). - If
IsConstructor (C) istrue , then- LetthisRealm be
the current Realm Record . - LetrealmC be ?
GetFunctionRealm (C). - IfthisRealm andrealmC are not the same
Realm Record , then
- LetthisRealm be
- IfC
is an Object , then - IfC is
undefined , return ?ArrayCreate (length). - If
IsConstructor (C) isfalse , throw aTypeError exception. - Return ?
Construct (C, «𝔽 (length) »).
IforiginalArray was created using the standard built-in ArrayArray.prototype methods that now are defined using ArraySpeciesCreate.
10.4.2.4 ArraySetLength (A,Desc )
The abstract operation ArraySetLength takes argumentsA (an Array) andDesc (a
- IfDesc does not have a[[Value]] field, then
- Return !
OrdinaryDefineOwnProperty (A,"length" ,Desc).
- Return !
- LetnewLenDesc be a copy ofDesc.
- LetnewLen be ?
ToUint32 (Desc.[[Value]]). - LetnumberLen be ?
ToNumber (Desc.[[Value]]). - If
SameValueZero (newLen,numberLen) isfalse , throw aRangeError exception. - SetnewLenDesc.[[Value]] tonewLen.
- LetoldLenDesc be
OrdinaryGetOwnProperty (A,"length" ). Assert :IsDataDescriptor (oldLenDesc) istrue .Assert :oldLenDesc.[[Configurable]] isfalse .- LetoldLen beoldLenDesc.[[Value]].
- IfnewLen ≥oldLen, then
- Return !
OrdinaryDefineOwnProperty (A,"length" ,newLenDesc).
- Return !
- IfoldLenDesc.[[Writable]] is
false , returnfalse . - IfnewLenDesc does not have a[[Writable]] field ornewLenDesc.[[Writable]] is
true , then- LetnewWritable be
true .
- LetnewWritable be
- Else,
- NOTE: Setting the[[Writable]] attribute to
false is deferred in case any elements cannot be deleted. - LetnewWritable be
false . - SetnewLenDesc.[[Writable]] to
true .
- NOTE: Setting the[[Writable]] attribute to
- Letsucceeded be !
OrdinaryDefineOwnProperty (A,"length" ,newLenDesc). - Ifsucceeded is
false , returnfalse . - For each own
property key P ofA such thatP is anarray index and !ToUint32 (P) ≥newLen, in descending numeric index order, do- LetdeleteSucceeded be ! A.[[Delete]](P).
- IfdeleteSucceeded is
false , then- SetnewLenDesc.[[Value]] to !
ToUint32 (P) +1 𝔽. - IfnewWritable is
false , setnewLenDesc.[[Writable]] tofalse . - Perform !
OrdinaryDefineOwnProperty (A,"length" ,newLenDesc). - Return
false .
- SetnewLenDesc.[[Value]] to !
- IfnewWritable is
false , then- Setsucceeded to !
OrdinaryDefineOwnProperty (A,"length" , PropertyDescriptor {[[Writable]]:false }). Assert :succeeded istrue .
- Setsucceeded to !
- Return
true .
10.4.3 String Exotic Objects
A String object is an
An object is aString exotic object (or simply, a String object) if its[[GetOwnProperty]],[[DefineOwnProperty]], and[[OwnPropertyKeys]] internal methods use the following implementations, and its other essential internal methods use the definitions found in
10.4.3.1[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of a
- Letdesc be
OrdinaryGetOwnProperty (S,P). - Ifdesc is not
undefined , returndesc. - Return
StringGetOwnProperty (S,P).
10.4.3.2[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of a
- LetstringDesc be
StringGetOwnProperty (S,P). - IfstringDesc is not
undefined , then- Letextensible beS.[[Extensible]].
- Return
IsCompatiblePropertyDescriptor (extensible,Desc,stringDesc).
- Return !
OrdinaryDefineOwnProperty (S,P,Desc).
10.4.3.3[[OwnPropertyKeys]] ( )
The[[OwnPropertyKeys]] internal method of a
- Letkeys be a new empty
List . - Letstr beO.[[StringData]].
Assert :stris a String .- Letlen be the length ofstr.
- For each
integer i such that 0 ≤i <len, in ascending order, do - For each own
property key P ofO such thatP is anarray index and !ToIntegerOrInfinity (P) ≥len, in ascending numeric index order, do- AppendP tokeys.
- For each own
property key P ofO such thatPis a String andP is not anarray index , in ascending chronological order of property creation, do- AppendP tokeys.
- For each own
property key P ofO such thatPis a Symbol , in ascending chronological order of property creation, do- AppendP tokeys.
- Returnkeys.
10.4.3.4 StringCreate (value,prototype )
The abstract operation StringCreate takes argumentsvalue (a String) andprototype (an Object) and returns a
- LetS be
MakeBasicObject («[[Prototype]],[[Extensible]],[[StringData]] »). - SetS.[[Prototype]] toprototype.
- SetS.[[StringData]] tovalue.
- SetS.[[GetOwnProperty]] as specified in
10.4.3.1 . - SetS.[[DefineOwnProperty]] as specified in
10.4.3.2 . - SetS.[[OwnPropertyKeys]] as specified in
10.4.3.3 . - Letlength be the length ofvalue.
- Perform !
DefinePropertyOrThrow (S,"length" , PropertyDescriptor {[[Value]]:𝔽 (length),[[Writable]]:false ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnS.
10.4.3.5 StringGetOwnProperty (S,P )
The abstract operation StringGetOwnProperty takes argumentsS (an Object that has a[[StringData]] internal slot) andP (a
- IfP
is not a String , returnundefined . - Letindex be
CanonicalNumericIndexString (P). - Ifindex is
undefined , returnundefined . - If
IsIntegralNumber (index) isfalse , returnundefined . - Ifindex is
-0 𝔽, returnundefined . - Letstr beS.[[StringData]].
Assert :stris a String .- Letlen be the length ofstr.
- If
ℝ (index) < 0 orlen ≤ℝ (index), returnundefined . - LetresultStr be the
substring ofstr fromℝ (index) toℝ (index) + 1. - Return the PropertyDescriptor {[[Value]]:resultStr,[[Writable]]:
false ,[[Enumerable]]:true ,[[Configurable]]:false }.
10.4.4 Arguments Exotic Objects
Most ECMAScript functions make an arguments object available to their code. Depending upon the characteristics of the function definition, its arguments object is either an
An object is anarguments exotic object if its internal methods use the following implementations, with the ones not specified here using those found in
While
Object.prototype.toString (
The
The ParameterMap object and its property values are used as a device for specifying the arguments object correspondence to argument bindings. The ParameterMap object and the objects that are the values of its properties are not directly observable from ECMAScript code. An ECMAScript implementation does not need to actually create or use such objects to implement the specified semantics.
Ordinary arguments objects define a non-configurable
ECMAScript implementations of
10.4.4.1[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of an
- Letdesc be
OrdinaryGetOwnProperty (args,P). - Ifdesc is
undefined , returnundefined . - Letmap beargs.[[ParameterMap]].
- LetisMapped be !
HasOwnProperty (map,P). - IfisMapped is
true , then- Setdesc.[[Value]] to !
Get (map,P).
- Setdesc.[[Value]] to !
- Returndesc.
10.4.4.2[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of an
- Letmap beargs.[[ParameterMap]].
- LetisMapped be !
HasOwnProperty (map,P). - LetnewArgDesc beDesc.
- IfisMapped is
true andIsDataDescriptor (Desc) istrue , then- IfDesc does not have a[[Value]] field,Desc has a[[Writable]] field, andDesc.[[Writable]] is
false , then- SetnewArgDesc to a copy ofDesc.
- SetnewArgDesc.[[Value]] to !
Get (map,P).
- IfDesc does not have a[[Value]] field,Desc has a[[Writable]] field, andDesc.[[Writable]] is
- Letallowed be !
OrdinaryDefineOwnProperty (args,P,newArgDesc). - Ifallowed is
false , returnfalse . - IfisMapped is
true , then- If
IsAccessorDescriptor (Desc) istrue , then- Perform ! map.[[Delete]](P).
- Else,
- If
- Return
true .
10.4.4.3[[Get]] (P,Receiver )
The[[Get]] internal method of an
- Letmap beargs.[[ParameterMap]].
- LetisMapped be !
HasOwnProperty (map,P). - IfisMapped is
false , then- Return ?
OrdinaryGet (args,P,Receiver).
- Return ?
- Else,
10.4.4.4[[Set]] (P,V,Receiver )
The[[Set]] internal method of an
- If
SameValue (args,Receiver) isfalse , then- LetisMapped be
false .
- LetisMapped be
- Else,
- Letmap beargs.[[ParameterMap]].
- LetisMapped be !
HasOwnProperty (map,P).
- IfisMapped is
true , then - Return ?
OrdinarySet (args,P,V,Receiver).
10.4.4.5[[Delete]] (P )
The[[Delete]] internal method of an
- Letmap beargs.[[ParameterMap]].
- LetisMapped be !
HasOwnProperty (map,P). - Letresult be ?
OrdinaryDelete (args,P). - Ifresult is
true andisMapped istrue , then- Perform ! map.[[Delete]](P).
- Returnresult.
10.4.4.6 CreateUnmappedArgumentsObject (argumentsList )
The abstract operation CreateUnmappedArgumentsObject takes argumentargumentsList (a
- Letlen be the number of elements inargumentsList.
- Letobj be
OrdinaryObjectCreate (%Object.prototype% , «[[ParameterMap]] »). - Setobj.[[ParameterMap]] to
undefined . - Perform !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor {[[Value]]:𝔽 (len),[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:true }). - Letindex be 0.
- Repeat, whileindex <len,
- Letval beargumentsList[index].
- Perform !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)),val). - Setindex toindex + 1.
- Perform !
DefinePropertyOrThrow (obj,@@iterator , PropertyDescriptor {[[Value]]: %Array.prototype.values%,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor {[[Get]]:%ThrowTypeError% ,[[Set]]:%ThrowTypeError% ,[[Enumerable]]:false ,[[Configurable]]:false }). - Returnobj.
10.4.4.7 CreateMappedArgumentsObject (func,formals,argumentsList,env )
The abstract operation CreateMappedArgumentsObject takes argumentsfunc (an Object),formals (a
Assert :formals does not contain a rest parameter, any binding patterns, or any initializers. It may contain duplicate identifiers.- Letlen be the number of elements inargumentsList.
- Letobj be
MakeBasicObject («[[Prototype]],[[Extensible]],[[ParameterMap]] »). - Setobj.[[GetOwnProperty]] as specified in
10.4.4.1 . - Setobj.[[DefineOwnProperty]] as specified in
10.4.4.2 . - Setobj.[[Get]] as specified in
10.4.4.3 . - Setobj.[[Set]] as specified in
10.4.4.4 . - Setobj.[[Delete]] as specified in
10.4.4.5 . - Setobj.[[Prototype]] to
%Object.prototype% . - Letmap be
OrdinaryObjectCreate (null ). - Setobj.[[ParameterMap]] tomap.
- LetparameterNames be the
BoundNames offormals. - LetnumberOfParameters be the number of elements inparameterNames.
- Letindex be 0.
- Repeat, whileindex <len,
- Letval beargumentsList[index].
- Perform !
CreateDataPropertyOrThrow (obj, !ToString (𝔽 (index)),val). - Setindex toindex + 1.
- Perform !
DefinePropertyOrThrow (obj,"length" , PropertyDescriptor {[[Value]]:𝔽 (len),[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:true }). - LetmappedNames be a new empty
List . - Setindex tonumberOfParameters - 1.
- Repeat, whileindex ≥ 0,
- Letname beparameterNames[index].
- IfmappedNames does not containname, then
- Appendname tomappedNames.
- Ifindex <len, then
- Letg be
MakeArgGetter (name,env). - Letp be
MakeArgSetter (name,env). - Perform ! map.[[DefineOwnProperty]](!
ToString (𝔽 (index)), PropertyDescriptor {[[Set]]:p,[[Get]]:g,[[Enumerable]]:false ,[[Configurable]]:true }).
- Letg be
- Setindex toindex - 1.
- Perform !
DefinePropertyOrThrow (obj,@@iterator , PropertyDescriptor {[[Value]]: %Array.prototype.values%,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:true }). - Perform !
DefinePropertyOrThrow (obj,"callee" , PropertyDescriptor {[[Value]]:func,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:true }). - Returnobj.
10.4.4.7.1 MakeArgGetter (name,env )
The abstract operation MakeArgGetter takes argumentsname (a String) andenv (an
- LetgetterClosure be a new
Abstract Closure with no parameters that capturesname andenv and performs the following steps when called:- Returnenv.GetBindingValue(name,
false ).
- Returnenv.GetBindingValue(name,
- Letgetter be
CreateBuiltinFunction (getterClosure, 0,"" , « »). - NOTE:getter is never directly accessible to ECMAScript code.
- Returngetter.
10.4.4.7.2 MakeArgSetter (name,env )
The abstract operation MakeArgSetter takes argumentsname (a String) andenv (an
- LetsetterClosure be a new
Abstract Closure with parameters (value) that capturesname andenv and performs the following steps when called:- Return ! env.SetMutableBinding(name,value,
false ).
- Return ! env.SetMutableBinding(name,value,
- Letsetter be
CreateBuiltinFunction (setterClosure, 1,"" , « »). - NOTE:setter is never directly accessible to ECMAScript code.
- Returnsetter.
10.4.5 TypedArray Exotic Objects
A
An object is aTypedArray if its[[GetOwnProperty]],[[HasProperty]],[[DefineOwnProperty]],[[Get]],[[Set]],[[Delete]], and[[OwnPropertyKeys]] internal methods use the definitions in this section, and its other essential internal methods use the definitions found in
10.4.5.1[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , then- Letvalue be
TypedArrayGetElement (O,numericIndex). - Ifvalue is
undefined , returnundefined . - Return the PropertyDescriptor {[[Value]]:value,[[Writable]]:
true ,[[Enumerable]]:true ,[[Configurable]]:true }.
- Letvalue be
- LetnumericIndex be
- Return
OrdinaryGetOwnProperty (O,P).
10.4.5.2[[HasProperty]] (P )
The[[HasProperty]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , returnIsValidIntegerIndex (O,numericIndex).
- LetnumericIndex be
- Return ?
OrdinaryHasProperty (O,P).
10.4.5.3[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , then- If
IsValidIntegerIndex (O,numericIndex) isfalse , returnfalse . - IfDesc has a[[Configurable]] field andDesc.[[Configurable]] is
false , returnfalse . - IfDesc has an[[Enumerable]] field andDesc.[[Enumerable]] is
false , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - IfDesc has a[[Writable]] field andDesc.[[Writable]] is
false , returnfalse . - IfDesc has a[[Value]] field, perform ?
TypedArraySetElement (O,numericIndex,Desc.[[Value]]). - Return
true .
- If
- LetnumericIndex be
- Return !
OrdinaryDefineOwnProperty (O,P,Desc).
10.4.5.4[[Get]] (P,Receiver )
The[[Get]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , then- Return
TypedArrayGetElement (O,numericIndex).
- Return
- LetnumericIndex be
- Return ?
OrdinaryGet (O,P,Receiver).
10.4.5.5[[Set]] (P,V,Receiver )
The[[Set]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , then- If
SameValue (O,Receiver) istrue , then- Perform ?
TypedArraySetElement (O,numericIndex,V). - Return
true .
- Perform ?
- If
IsValidIntegerIndex (O,numericIndex) isfalse , returntrue .
- If
- LetnumericIndex be
- Return ?
OrdinarySet (O,P,V,Receiver).
10.4.5.6[[Delete]] (P )
The[[Delete]] internal method of a
- IfP
is a String , then- LetnumericIndex be
CanonicalNumericIndexString (P). - IfnumericIndex is not
undefined , then- If
IsValidIntegerIndex (O,numericIndex) isfalse , returntrue ; else returnfalse .
- If
- LetnumericIndex be
- Return !
OrdinaryDelete (O,P).
10.4.5.7[[OwnPropertyKeys]] ( )
The[[OwnPropertyKeys]] internal method of a
- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Letkeys be a new empty
List . - If
IsTypedArrayOutOfBounds (taRecord) isfalse , then- Letlength be
TypedArrayLength (taRecord). - For each
integer i such that 0 ≤i <length, in ascending order, do
- Letlength be
- For each own
property key P ofO such thatPis a String andP is not aninteger index , in ascending chronological order of property creation, do- AppendP tokeys.
- For each own
property key P ofO such thatPis a Symbol , in ascending chronological order of property creation, do- AppendP tokeys.
- Returnkeys.
10.4.5.8 TypedArray With Buffer Witness Records
AnTypedArray With Buffer Witness Record is a
TypedArray With Buffer Witness Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Object]] | a | The |
| [[CachedBufferByteLength]] | a non-negative | The byte length of the object's[[ViewedArrayBuffer]] when the |
10.4.5.9 MakeTypedArrayWithBufferWitnessRecord (obj,order )
The abstract operation MakeTypedArrayWithBufferWitnessRecord takes argumentsobj (a
- Letbuffer beobj.[[ViewedArrayBuffer]].
- If
IsDetachedBuffer (buffer) istrue , then- LetbyteLength be
detached .
- LetbyteLength be
- Else,
- LetbyteLength be
ArrayBufferByteLength (buffer,order).
- LetbyteLength be
- Return the
TypedArray With Buffer Witness Record {[[Object]]:obj,[[CachedBufferByteLength]]:byteLength }.
10.4.5.10 TypedArrayCreate (prototype )
The abstract operation TypedArrayCreate takes argumentprototype (an Object) and returns a
- LetinternalSlotsList be «[[Prototype]],[[Extensible]],[[ViewedArrayBuffer]],[[TypedArrayName]],[[ContentType]],[[ByteLength]],[[ByteOffset]],[[ArrayLength]] ».
- LetA be
MakeBasicObject (internalSlotsList). - SetA.[[GetOwnProperty]] as specified in
10.4.5.1 . - SetA.[[HasProperty]] as specified in
10.4.5.2 . - SetA.[[DefineOwnProperty]] as specified in
10.4.5.3 . - SetA.[[Get]] as specified in
10.4.5.4 . - SetA.[[Set]] as specified in
10.4.5.5 . - SetA.[[Delete]] as specified in
10.4.5.6 . - SetA.[[OwnPropertyKeys]] as specified in
10.4.5.7 . - SetA.[[Prototype]] toprototype.
- ReturnA.
10.4.5.11 TypedArrayByteLength (taRecord )
The abstract operation TypedArrayByteLength takes argumenttaRecord (a
- If
IsTypedArrayOutOfBounds (taRecord) istrue , return 0. - Letlength be
TypedArrayLength (taRecord). - Iflength = 0, return 0.
- LetO betaRecord.[[Object]].
- IfO.[[ByteLength]] is not
auto , returnO.[[ByteLength]]. - LetelementSize be
TypedArrayElementSize (O). - Returnlength ×elementSize.
10.4.5.12 TypedArrayLength (taRecord )
The abstract operation TypedArrayLength takes argumenttaRecord (a
Assert :IsTypedArrayOutOfBounds (taRecord) isfalse .- LetO betaRecord.[[Object]].
- IfO.[[ArrayLength]] is not
auto , returnO.[[ArrayLength]]. Assert :IsFixedLengthArrayBuffer (O.[[ViewedArrayBuffer]]) isfalse .- LetbyteOffset beO.[[ByteOffset]].
- LetelementSize be
TypedArrayElementSize (O). - LetbyteLength betaRecord.[[CachedBufferByteLength]].
Assert :byteLength is notdetached .- Return
floor ((byteLength -byteOffset) /elementSize).
10.4.5.13 IsTypedArrayOutOfBounds (taRecord )
The abstract operation IsTypedArrayOutOfBounds takes argumenttaRecord (a
- LetO betaRecord.[[Object]].
- LetbufferByteLength betaRecord.[[CachedBufferByteLength]].
Assert :IsDetachedBuffer (O.[[ViewedArrayBuffer]]) istrue if and only ifbufferByteLength isdetached .- IfbufferByteLength is
detached , returntrue . - LetbyteOffsetStart beO.[[ByteOffset]].
- IfO.[[ArrayLength]] is
auto , then- LetbyteOffsetEnd bebufferByteLength.
- Else,
- LetelementSize be
TypedArrayElementSize (O). - LetbyteOffsetEnd bebyteOffsetStart +O.[[ArrayLength]] ×elementSize.
- LetelementSize be
- IfbyteOffsetStart >bufferByteLength orbyteOffsetEnd >bufferByteLength, return
true . - NOTE: 0-length
TypedArrays are not considered out-of-bounds. - Return
false .
10.4.5.14 IsValidIntegerIndex (O,index )
The abstract operation IsValidIntegerIndex takes argumentsO (a
- If
IsDetachedBuffer (O.[[ViewedArrayBuffer]]) istrue , returnfalse . - If
IsIntegralNumber (index) isfalse , returnfalse . - Ifindex is
-0 𝔽, returnfalse . - LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,unordered ). - NOTE: Bounds checking is not a synchronizing operation whenO's backing buffer is a
growable SharedArrayBuffer . - If
IsTypedArrayOutOfBounds (taRecord) istrue , returnfalse . - Letlength be
TypedArrayLength (taRecord). - If
ℝ (index) < 0 orℝ (index) ≥length, returnfalse . - Return
true .
10.4.5.15 TypedArrayGetElement (O,index )
The abstract operation TypedArrayGetElement takes argumentsO (a
- If
IsValidIntegerIndex (O,index) isfalse , returnundefined . - Letoffset beO.[[ByteOffset]].
- LetelementSize be
TypedArrayElementSize (O). - LetbyteIndexInBuffer be (
ℝ (index) ×elementSize) +offset. - LetelementType be
TypedArrayElementType (O). - Return
GetValueFromBuffer (O.[[ViewedArrayBuffer]],byteIndexInBuffer,elementType,true ,unordered ).
10.4.5.16 TypedArraySetElement (O,index,value )
The abstract operation TypedArraySetElement takes argumentsO (a
- IfO.[[ContentType]] is
bigint , letnumValue be ?ToBigInt (value). - Otherwise, letnumValue be ?
ToNumber (value). - If
IsValidIntegerIndex (O,index) istrue , then- Letoffset beO.[[ByteOffset]].
- LetelementSize be
TypedArrayElementSize (O). - LetbyteIndexInBuffer be (
ℝ (index) ×elementSize) +offset. - LetelementType be
TypedArrayElementType (O). - Perform
SetValueInBuffer (O.[[ViewedArrayBuffer]],byteIndexInBuffer,elementType,numValue,true ,unordered ).
- Return
unused .
This operation always appears to succeed, but it has no effect when attempting to write past the end of a
10.4.5.17 IsArrayBufferViewOutOfBounds (O )
The abstract operation IsArrayBufferViewOutOfBounds takes argumentO (a
- IfO has a[[DataView]] internal slot, then
- LetviewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - Return
IsViewOutOfBounds (viewRecord).
- LetviewRecord be
- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Return
IsTypedArrayOutOfBounds (taRecord).
10.4.6 Module Namespace Exotic Objects
Aexport * export items. Each String-valued own
An object is amodule namespace exotic object if its[[GetPrototypeOf]],[[SetPrototypeOf]],[[IsExtensible]],[[PreventExtensions]],[[GetOwnProperty]],[[DefineOwnProperty]],[[HasProperty]],[[Get]],[[Set]],[[Delete]], and[[OwnPropertyKeys]] internal methods use the definitions in this section, and its other essential internal methods use the definitions found in
| Internal Slot | Type | Description |
|---|---|---|
| [[Module]] | a | The |
| [[Exports]] | a | A |
10.4.6.1[[GetPrototypeOf]] ( )
The[[GetPrototypeOf]] internal method of a
- Return
null .
10.4.6.2[[SetPrototypeOf]] (V )
The[[SetPrototypeOf]] internal method of a
- Return !
SetImmutablePrototype (O,V).
10.4.6.3[[IsExtensible]] ( )
The[[IsExtensible]] internal method of a
- Return
false .
10.4.6.4[[PreventExtensions]] ( )
The[[PreventExtensions]] internal method of a
- Return
true .
10.4.6.5[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of a
- IfP
is a Symbol , returnOrdinaryGetOwnProperty (O,P). - Letexports beO.[[Exports]].
- Ifexports does not containP, return
undefined . - Letvalue be ? O.[[Get]](P,O).
- Return PropertyDescriptor {[[Value]]:value,[[Writable]]:
true ,[[Enumerable]]:true ,[[Configurable]]:false }.
10.4.6.6[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of a
- IfP
is a Symbol , return !OrdinaryDefineOwnProperty (O,P,Desc). - Letcurrent be ? O.[[GetOwnProperty]](P).
- Ifcurrent is
undefined , returnfalse . - IfDesc has a[[Configurable]] field andDesc.[[Configurable]] is
true , returnfalse . - IfDesc has an[[Enumerable]] field andDesc.[[Enumerable]] is
false , returnfalse . - If
IsAccessorDescriptor (Desc) istrue , returnfalse . - IfDesc has a[[Writable]] field andDesc.[[Writable]] is
false , returnfalse . - IfDesc has a[[Value]] field, return
SameValue (Desc.[[Value]],current.[[Value]]). - Return
true .
10.4.6.7[[HasProperty]] (P )
The[[HasProperty]] internal method of a
- IfP
is a Symbol , return !OrdinaryHasProperty (O,P). - Letexports beO.[[Exports]].
- Ifexports containsP, return
true . - Return
false .
10.4.6.8[[Get]] (P,Receiver )
The[[Get]] internal method of a
- IfP
is a Symbol , then- Return !
OrdinaryGet (O,P,Receiver).
- Return !
- Letexports beO.[[Exports]].
- Ifexports does not containP, return
undefined . - Letm beO.[[Module]].
- Letbinding bem.ResolveExport(P).
Assert :binding is aResolvedBinding Record .- LettargetModule bebinding.[[Module]].
Assert :targetModule is notundefined .- Ifbinding.[[BindingName]] is
namespace , then- Return
GetModuleNamespace (targetModule).
- Return
- LettargetEnv betargetModule.[[Environment]].
- IftargetEnv is
empty , throw aReferenceError exception. - Return ? targetEnv.GetBindingValue(binding.[[BindingName]],
true ).
ResolveExport is side-effect free. Each time this operation is called with a specificexportName,resolveSet pair as arguments it must return the same result. An implementation might choose to pre-compute or cache the ResolveExport results for the[[Exports]] of each
10.4.6.9[[Set]] (P,V,Receiver )
The[[Set]] internal method of a
- Return
false .
10.4.6.10[[Delete]] (P )
The[[Delete]] internal method of a
- IfP
is a Symbol , then- Return !
OrdinaryDelete (O,P).
- Return !
- Letexports beO.[[Exports]].
- Ifexports containsP, return
false . - Return
true .
10.4.6.11[[OwnPropertyKeys]] ( )
The[[OwnPropertyKeys]] internal method of a
- Letexports beO.[[Exports]].
- LetsymbolKeys be
OrdinaryOwnPropertyKeys (O). - Return the
list-concatenation ofexports andsymbolKeys.
10.4.6.12 ModuleNamespaceCreate (module,exports )
The abstract operation ModuleNamespaceCreate takes argumentsmodule (a
Assert :module.[[Namespace]] isempty .- LetinternalSlotsList be the internal slots listed in
Table 33 . - LetM be
MakeBasicObject (internalSlotsList). - SetM's essential internal methods to the definitions specified in
10.4.6 . - SetM.[[Module]] tomodule.
- LetsortedExports be a
List whose elements are the elements ofexports ordered as if an Array of the same values had been sorted using %Array.prototype.sort% usingundefined ascomparefn. - SetM.[[Exports]] tosortedExports.
- Create own properties ofM corresponding to the definitions in
28.3 . - Setmodule.[[Namespace]] toM.
- ReturnM.
10.4.7 Immutable Prototype Exotic Objects
An
An object is animmutable prototype exotic object if its[[SetPrototypeOf]] internal method uses the following implementation. (Its other essential internal methods may use any implementation, depending on the specific
Unlike other
10.4.7.1[[SetPrototypeOf]] (V )
The[[SetPrototypeOf]] internal method of an
- Return ?
SetImmutablePrototype (O,V).
10.4.7.2 SetImmutablePrototype (O,V )
The abstract operation SetImmutablePrototype takes argumentsO (an Object) andV (an Object or
- Letcurrent be ? O.[[GetPrototypeOf]]().
- If
SameValue (V,current) istrue , returntrue . - Return
false .
10.5 Proxy Object Internal Methods and Internal Slots
A Proxy object is an
An object is aProxy exotic object if its essential internal methods (including[[Call]] and[[Construct]], if applicable) use the definitions in this section. These internal methods are installed in
| Internal Method | Handler Method |
|---|---|
| [[GetPrototypeOf]] | getPrototypeOf |
| [[SetPrototypeOf]] | setPrototypeOf |
| [[IsExtensible]] | isExtensible |
| [[PreventExtensions]] | preventExtensions |
| [[GetOwnProperty]] | getOwnPropertyDescriptor |
| [[DefineOwnProperty]] | defineProperty |
| [[HasProperty]] | has |
| [[Get]] | get |
| [[Set]] | set |
| [[Delete]] | deleteProperty |
| [[OwnPropertyKeys]] | ownKeys |
| [[Call]] | apply |
| [[Construct]] | construct |
When a handler method is called to provide the implementation of a Proxy object internal method, the handler method is passed the proxy's target object as a parameter. A proxy's handler object does not necessarily have a method corresponding to every essential internal method. Invoking an internal method on the proxy results in the invocation of the corresponding internal method on the proxy's target object if the handler object does not have a method corresponding to the internal trap.
The[[ProxyHandler]] and[[ProxyTarget]] internal slots of a Proxy object are always initialized when the object is created and typically may not be modified. Some Proxy objects are created in a manner that permits them to be subsequentlyrevoked. When a proxy is revoked, its[[ProxyHandler]] and[[ProxyTarget]] internal slots are set to
Because Proxy objects permit the implementation of internal methods to be provided by arbitrary ECMAScript code, it is possible to define a Proxy object whose handler methods violates the invariants defined in
In the following algorithm descriptions, assumeO is an ECMAScript Proxy object,P is a
10.5.1[[GetPrototypeOf]] ( )
The[[GetPrototypeOf]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"getPrototypeOf" ). - Iftrap is
undefined , then- Return ? target.[[GetPrototypeOf]]().
- LethandlerProto be ?
Call (trap,handler, «target »). - IfhandlerProto
is not an Object andhandlerProto is notnull , throw aTypeError exception. - LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
true , returnhandlerProto. - LettargetProto be ? target.[[GetPrototypeOf]]().
- If
SameValue (handlerProto,targetProto) isfalse , throw aTypeError exception. - ReturnhandlerProto.
[[GetPrototypeOf]] for Proxy objects enforces the following invariants:
- The result of[[GetPrototypeOf]] must be either an Object or
null . - If the target object is not extensible,[[GetPrototypeOf]] applied to the Proxy object must return the same value as[[GetPrototypeOf]] applied to the Proxy object's target object.
10.5.2[[SetPrototypeOf]] (V )
The[[SetPrototypeOf]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"setPrototypeOf" ). - Iftrap is
undefined , then- Return ? target.[[SetPrototypeOf]](V).
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target,V »)). - IfbooleanTrapResult is
false , returnfalse . - LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
true , returntrue . - LettargetProto be ? target.[[GetPrototypeOf]]().
- If
SameValue (V,targetProto) isfalse , throw aTypeError exception. - Return
true .
[[SetPrototypeOf]] for Proxy objects enforces the following invariants:
- The result of[[SetPrototypeOf]]
is a Boolean value. - If the target object is not extensible, the argument value must be the same as the result of[[GetPrototypeOf]] applied to target object.
10.5.3[[IsExtensible]] ( )
The[[IsExtensible]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"isExtensible" ). - Iftrap is
undefined , then- Return ?
IsExtensible (target).
- Return ?
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target »)). - LettargetResult be ?
IsExtensible (target). - IfbooleanTrapResult is nottargetResult, throw a
TypeError exception. - ReturnbooleanTrapResult.
[[IsExtensible]] for Proxy objects enforces the following invariants:
- The result of[[IsExtensible]]
is a Boolean value. - [[IsExtensible]] applied to the Proxy object must return the same value as[[IsExtensible]] applied to the Proxy object's target object with the same argument.
10.5.4[[PreventExtensions]] ( )
The[[PreventExtensions]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"preventExtensions" ). - Iftrap is
undefined , then- Return ? target.[[PreventExtensions]]().
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target »)). - IfbooleanTrapResult is
true , then- LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
true , throw aTypeError exception.
- LetextensibleTarget be ?
- ReturnbooleanTrapResult.
[[PreventExtensions]] for Proxy objects enforces the following invariants:
- The result of[[PreventExtensions]]
is a Boolean value. - [[PreventExtensions]] applied to the Proxy object only returns
true if[[IsExtensible]] applied to the Proxy object's target object isfalse .
10.5.5[[GetOwnProperty]] (P )
The[[GetOwnProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"getOwnPropertyDescriptor" ). - Iftrap is
undefined , then- Return ? target.[[GetOwnProperty]](P).
- LettrapResultObj be ?
Call (trap,handler, «target,P »). - IftrapResultObj
is not an Object andtrapResultObj is notundefined , throw aTypeError exception. - LettargetDesc be ? target.[[GetOwnProperty]](P).
- IftrapResultObj is
undefined , then- IftargetDesc is
undefined , returnundefined . - IftargetDesc.[[Configurable]] is
false , throw aTypeError exception. - LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
false , throw aTypeError exception. - Return
undefined .
- IftargetDesc is
- LetextensibleTarget be ?
IsExtensible (target). - LetresultDesc be ?
ToPropertyDescriptor (trapResultObj). - Perform
CompletePropertyDescriptor (resultDesc). - Letvalid be
IsCompatiblePropertyDescriptor (extensibleTarget,resultDesc,targetDesc). - Ifvalid is
false , throw aTypeError exception. - IfresultDesc.[[Configurable]] is
false , then- IftargetDesc is
undefined ortargetDesc.[[Configurable]] istrue , then- Throw a
TypeError exception.
- Throw a
- IfresultDesc has a[[Writable]] field andresultDesc.[[Writable]] is
false , thenAssert :targetDesc has a[[Writable]] field.- IftargetDesc.[[Writable]] is
true , throw aTypeError exception.
- IftargetDesc is
- ReturnresultDesc.
[[GetOwnProperty]] for Proxy objects enforces the following invariants:
- The result of[[GetOwnProperty]] must be either an Object or
undefined . - A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as non-existent, if it exists as an own property of a non-extensible target object.
- A property cannot be reported as existent, if it does not exist as an own property of the target object and the target object is not extensible.
- A property cannot be reported as non-configurable, unless it exists as a non-configurable own property of the target object.
- A property cannot be reported as both non-configurable and non-writable, unless it exists as a non-configurable, non-writable own property of the target object.
10.5.6[[DefineOwnProperty]] (P,Desc )
The[[DefineOwnProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"defineProperty" ). - Iftrap is
undefined , then- Return ? target.[[DefineOwnProperty]](P,Desc).
- LetdescObj be
FromPropertyDescriptor (Desc). - LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target,P,descObj »)). - IfbooleanTrapResult is
false , returnfalse . - LettargetDesc be ? target.[[GetOwnProperty]](P).
- LetextensibleTarget be ?
IsExtensible (target). - IfDesc has a[[Configurable]] field andDesc.[[Configurable]] is
false , then- LetsettingConfigFalse be
true .
- LetsettingConfigFalse be
- Else,
- LetsettingConfigFalse be
false .
- LetsettingConfigFalse be
- IftargetDesc is
undefined , then- IfextensibleTarget is
false , throw aTypeError exception. - IfsettingConfigFalse is
true , throw aTypeError exception.
- IfextensibleTarget is
- Else,
- If
IsCompatiblePropertyDescriptor (extensibleTarget,Desc,targetDesc) isfalse , throw aTypeError exception. - IfsettingConfigFalse is
true andtargetDesc.[[Configurable]] istrue , throw aTypeError exception. - If
IsDataDescriptor (targetDesc) istrue ,targetDesc.[[Configurable]] isfalse , andtargetDesc.[[Writable]] istrue , then- IfDesc has a[[Writable]] field andDesc.[[Writable]] is
false , throw aTypeError exception.
- IfDesc has a[[Writable]] field andDesc.[[Writable]] is
- If
- Return
true .
[[DefineOwnProperty]] for Proxy objects enforces the following invariants:
- The result of[[DefineOwnProperty]]
is a Boolean value. - A property cannot be added, if the target object is not extensible.
- A property cannot be non-configurable, unless there exists a corresponding non-configurable own property of the target object.
- A non-configurable property cannot be non-writable, unless there exists a corresponding non-configurable, non-writable own property of the target object.
- If a property has a corresponding target object property then applying the
Property Descriptor of the property to the target object using[[DefineOwnProperty]] will not throw an exception.
10.5.7[[HasProperty]] (P )
The[[HasProperty]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"has" ). - Iftrap is
undefined , then- Return ? target.[[HasProperty]](P).
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target,P »)). - IfbooleanTrapResult is
false , then- LettargetDesc be ? target.[[GetOwnProperty]](P).
- IftargetDesc is not
undefined , then- IftargetDesc.[[Configurable]] is
false , throw aTypeError exception. - LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
false , throw aTypeError exception.
- IftargetDesc.[[Configurable]] is
- ReturnbooleanTrapResult.
[[HasProperty]] for Proxy objects enforces the following invariants:
- The result of[[HasProperty]]
is a Boolean value. - A property cannot be reported as non-existent, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as non-existent, if it exists as an own property of the target object and the target object is not extensible.
10.5.8[[Get]] (P,Receiver )
The[[Get]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"get" ). - Iftrap is
undefined , then- Return ? target.[[Get]](P,Receiver).
- LettrapResult be ?
Call (trap,handler, «target,P,Receiver »). - LettargetDesc be ? target.[[GetOwnProperty]](P).
- IftargetDesc is not
undefined andtargetDesc.[[Configurable]] isfalse , then- If
IsDataDescriptor (targetDesc) istrue andtargetDesc.[[Writable]] isfalse , then- If
SameValue (trapResult,targetDesc.[[Value]]) isfalse , throw aTypeError exception.
- If
- If
IsAccessorDescriptor (targetDesc) istrue andtargetDesc.[[Get]] isundefined , then- IftrapResult is not
undefined , throw aTypeError exception.
- IftrapResult is not
- If
- ReturntrapResult.
[[Get]] for Proxy objects enforces the following invariants:
- The value reported for a property must be the same as the value of the corresponding target object property if the target object property is a non-writable, non-configurable own
data property . - The value reported for a property must be
undefined if the corresponding target object property is a non-configurable ownaccessor property that hasundefined as its[[Get]] attribute.
10.5.9[[Set]] (P,V,Receiver )
The[[Set]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"set" ). - Iftrap is
undefined , then- Return ? target.[[Set]](P,V,Receiver).
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target,P,V,Receiver »)). - IfbooleanTrapResult is
false , returnfalse . - LettargetDesc be ? target.[[GetOwnProperty]](P).
- IftargetDesc is not
undefined andtargetDesc.[[Configurable]] isfalse , then- If
IsDataDescriptor (targetDesc) istrue andtargetDesc.[[Writable]] isfalse , then- If
SameValue (V,targetDesc.[[Value]]) isfalse , throw aTypeError exception.
- If
- If
IsAccessorDescriptor (targetDesc) istrue , then- IftargetDesc.[[Set]] is
undefined , throw aTypeError exception.
- IftargetDesc.[[Set]] is
- If
- Return
true .
[[Set]] for Proxy objects enforces the following invariants:
- The result of[[Set]]
is a Boolean value. - Cannot change the value of a property to be different from the value of the corresponding target object property if the corresponding target object property is a non-writable, non-configurable own
data property . - Cannot set the value of a property if the corresponding target object property is a non-configurable own
accessor property that hasundefined as its[[Set]] attribute.
10.5.10[[Delete]] (P )
The[[Delete]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"deleteProperty" ). - Iftrap is
undefined , then- Return ? target.[[Delete]](P).
- LetbooleanTrapResult be
ToBoolean (?Call (trap,handler, «target,P »)). - IfbooleanTrapResult is
false , returnfalse . - LettargetDesc be ? target.[[GetOwnProperty]](P).
- IftargetDesc is
undefined , returntrue . - IftargetDesc.[[Configurable]] is
false , throw aTypeError exception. - LetextensibleTarget be ?
IsExtensible (target). - IfextensibleTarget is
false , throw aTypeError exception. - Return
true .
[[Delete]] for Proxy objects enforces the following invariants:
- The result of[[Delete]]
is a Boolean value. - A property cannot be reported as deleted, if it exists as a non-configurable own property of the target object.
- A property cannot be reported as deleted, if it exists as an own property of the target object and the target object is non-extensible.
10.5.11[[OwnPropertyKeys]] ( )
The[[OwnPropertyKeys]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"ownKeys" ). - Iftrap is
undefined , then- Return ? target.[[OwnPropertyKeys]]().
- LettrapResultArray be ?
Call (trap,handler, «target »). - LettrapResult be ?
CreateListFromArrayLike (trapResultArray, « String, Symbol »). - IftrapResult contains any duplicate entries, throw a
TypeError exception. - LetextensibleTarget be ?
IsExtensible (target). - LettargetKeys be ? target.[[OwnPropertyKeys]]().
Assert :targetKeys is aList ofproperty keys .Assert :targetKeys contains no duplicate entries.- LettargetConfigurableKeys be a new empty
List . - LettargetNonconfigurableKeys be a new empty
List . - For each elementkey oftargetKeys, do
- Letdesc be ? target.[[GetOwnProperty]](key).
- Ifdesc is not
undefined anddesc.[[Configurable]] isfalse , then- Appendkey totargetNonconfigurableKeys.
- Else,
- Appendkey totargetConfigurableKeys.
- IfextensibleTarget is
true andtargetNonconfigurableKeys is empty, then- ReturntrapResult.
- LetuncheckedResultKeys be a
List whose elements are the elements oftrapResult. - For each elementkey oftargetNonconfigurableKeys, do
- IfuncheckedResultKeys does not containkey, throw a
TypeError exception. - Removekey fromuncheckedResultKeys.
- IfuncheckedResultKeys does not containkey, throw a
- IfextensibleTarget is
true , returntrapResult. - For each elementkey oftargetConfigurableKeys, do
- IfuncheckedResultKeys does not containkey, throw a
TypeError exception. - Removekey fromuncheckedResultKeys.
- IfuncheckedResultKeys does not containkey, throw a
- IfuncheckedResultKeys is not empty, throw a
TypeError exception. - ReturntrapResult.
[[OwnPropertyKeys]] for Proxy objects enforces the following invariants:
- The result of[[OwnPropertyKeys]] is a
List . - The returned
List contains no duplicate entries. - The Type of each result
List element is either String or Symbol. - The result
List must contain the keys of all non-configurable own properties of the target object. - If the target object is not extensible, then the result
List must contain all the keys of the own properties of the target object and no other values.
10.5.12[[Call]] (thisArgument,argumentsList )
The[[Call]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"apply" ). - Iftrap is
undefined , then- Return ?
Call (target,thisArgument,argumentsList).
- Return ?
- LetargArray be
CreateArrayFromList (argumentsList). - Return ?
Call (trap,handler, «target,thisArgument,argArray »).
A
10.5.13[[Construct]] (argumentsList,newTarget )
The[[Construct]] internal method of a
- Perform ?
ValidateNonRevokedProxy (O). - Lettarget beO.[[ProxyTarget]].
Assert :IsConstructor (target) istrue .- Lethandler beO.[[ProxyHandler]].
Assert :handleris an Object .- Lettrap be ?
GetMethod (handler,"construct" ). - Iftrap is
undefined , then- Return ?
Construct (target,argumentsList,newTarget).
- Return ?
- LetargArray be
CreateArrayFromList (argumentsList). - LetnewObj be ?
Call (trap,handler, «target,argArray,newTarget »). - IfnewObj
is not an Object , throw aTypeError exception. - ReturnnewObj.
A
[[Construct]] for Proxy objects enforces the following invariants:
- The result of[[Construct]] must be an Object.
10.5.14 ValidateNonRevokedProxy (proxy )
The abstract operation ValidateNonRevokedProxy takes argumentproxy (a
- Ifproxy.[[ProxyTarget]] is
null , throw aTypeError exception. Assert :proxy.[[ProxyHandler]] is notnull .- Return
unused .
10.5.15 ProxyCreate (target,handler )
The abstract operation ProxyCreate takes argumentstarget (an
- Iftarget
is not an Object , throw aTypeError exception. - Ifhandler
is not an Object , throw aTypeError exception. - LetP be
MakeBasicObject («[[ProxyHandler]],[[ProxyTarget]] »). - SetP's essential internal methods, except for[[Call]] and[[Construct]], to the definitions specified in
10.5 . - If
IsCallable (target) istrue , then- SetP.[[Call]] as specified in
10.5.12 . - If
IsConstructor (target) istrue , then- SetP.[[Construct]] as specified in
10.5.13 .
- SetP.[[Construct]] as specified in
- SetP.[[Call]] as specified in
- SetP.[[ProxyTarget]] totarget.
- SetP.[[ProxyHandler]] tohandler.
- ReturnP.
11 ECMAScript Language: Source Text
11.1 Source Text
Syntax
ECMAScript source text is a sequence of Unicode code points. All Unicode code point values from U+0000 to U+10FFFF, including surrogate code points, may occur in ECMAScript source text where permitted by the ECMAScript grammars. The actual encodings used to store and interchange ECMAScript source text is not relevant to this specification. Regardless of the external source text encoding, a conforming ECMAScript implementation processes the source text as if it was an equivalent sequence of
The components of a combining character sequence are treated as individual Unicode code points even though a user might think of the whole sequence as a single character.
In string literals, regular expression literals, template literals and identifiers, any Unicode code point may also be expressed using Unicode escape sequences that explicitly express a code point's numeric value. Within a comment, such an escape sequence is effectively ignored as part of the comment.
ECMAScript differs from the Java programming language in the behaviour of Unicode escape sequences. In a Java program, if the Unicode escape sequence\u000A, for example, occurs within a single-line comment, it is interpreted as a line terminator (Unicode code point U+000A is LINE FEED (LF)) and therefore the next code point is not part of the comment. Similarly, if the Unicode escape sequence\u000A occurs within a string literal in a Java program, it is likewise interpreted as a line terminator, which is not allowed within a string literal—one must write\n instead of\u000A to cause a LINE FEED (LF) to be part of the String value of a string literal. In an ECMAScript program, a Unicode escape sequence occurring within a comment is never interpreted and therefore cannot contribute to termination of the comment. Similarly, a Unicode escape sequence occurring within a string literal in an ECMAScript program always contributes to the literal and is never interpreted as a line terminator or as a code point that might terminate the string literal.
11.1.1 Static Semantics: UTF16EncodeCodePoint (cp )
The abstract operation UTF16EncodeCodePoint takes argumentcp (a Unicode code point) and returns a String. It performs the following steps when called:
Assert : 0 ≤cp ≤ 0x10FFFF.- Ifcp ≤ 0xFFFF, return the String value consisting of the code unit whose numeric value iscp.
- Letcu1 be the code unit whose numeric value is
floor ((cp - 0x10000) / 0x400) + 0xD800. - Letcu2 be the code unit whose numeric value is ((cp - 0x10000)
modulo 0x400) + 0xDC00. - Return the
string-concatenation ofcu1 andcu2.
11.1.2 Static Semantics: CodePointsToString (text )
The abstract operation CodePointsToString takes argumenttext (a sequence of Unicode code points) and returns a String. It convertstext into a String value, as described in
- Letresult be the empty String.
- For each code pointcp oftext, do
- Setresult to the
string-concatenation ofresult andUTF16EncodeCodePoint (cp).
- Setresult to the
- Returnresult.
11.1.3 Static Semantics: UTF16SurrogatePairToCodePoint (lead,trail )
The abstract operation UTF16SurrogatePairToCodePoint takes argumentslead (a code unit) andtrail (a code unit) and returns a code point. Two code units that form a UTF-16
Assert :lead is aleading surrogate andtrail is atrailing surrogate .- Letcp be (lead - 0xD800) × 0x400 + (trail - 0xDC00) + 0x10000.
- Return the code pointcp.
11.1.4 Static Semantics: CodePointAt (string,position )
The abstract operation CodePointAt takes argumentsstring (a String) andposition (a non-negative
- Letsize be the length ofstring.
Assert :position ≥ 0 andposition <size.- Letfirst be the code unit at indexposition withinstring.
- Letcp be the code point whose numeric value is the numeric value offirst.
- Iffirst is neither a
leading surrogate nor atrailing surrogate , then- Return the
Record {[[CodePoint]]:cp,[[CodeUnitCount]]: 1,[[IsUnpairedSurrogate]]:false }.
- Return the
- Iffirst is a
trailing surrogate orposition + 1 =size, then- Return the
Record {[[CodePoint]]:cp,[[CodeUnitCount]]: 1,[[IsUnpairedSurrogate]]:true }.
- Return the
- Letsecond be the code unit at indexposition + 1 withinstring.
- Ifsecond is not a
trailing surrogate , then- Return the
Record {[[CodePoint]]:cp,[[CodeUnitCount]]: 1,[[IsUnpairedSurrogate]]:true }.
- Return the
- Setcp to
UTF16SurrogatePairToCodePoint (first,second). - Return the
Record {[[CodePoint]]:cp,[[CodeUnitCount]]: 2,[[IsUnpairedSurrogate]]:false }.
11.1.5 Static Semantics: StringToCodePoints (string )
The abstract operation StringToCodePoints takes argumentstring (a String) and returns a
- LetcodePoints be a new empty
List . - Letsize be the length ofstring.
- Letposition be 0.
- Repeat, whileposition <size,
- Letcp be
CodePointAt (string,position). - Appendcp.[[CodePoint]] tocodePoints.
- Setposition toposition +cp.[[CodeUnitCount]].
- Letcp be
- ReturncodePoints.
11.1.6 Static Semantics: ParseText (sourceText,goalSymbol )
The abstract operation ParseText takes argumentssourceText (a sequence of Unicode code points) andgoalSymbol (a nonterminal in one of the ECMAScript grammars) and returns a
- Attempt to parsesourceText usinggoalSymbol as the
goal symbol , and analyse the parse result for anyearly error conditions. Parsing andearly error detection may be interleaved in animplementation-defined manner. - If the parse succeeded and no
early errors were found, return theParse Node (an instance ofgoalSymbol) at the root of the parse tree resulting from the parse. - Otherwise, return a
List of one or moreSyntaxError objects representing the parsing errors and/orearly errors . If more than one parsing error orearly error is present, the number and ordering of error objects in the list isimplementation-defined , but at least one must be present.
Consider a text that has an
See also clause
11.2 Types of Source Code
There are four types of ECMAScript code:
- Global code is source text that is treated as an ECMAScript
Script . The global code of a particularScript does not include any source text that is parsed as part of aFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression . - Eval code is the source text supplied to the built-in
evalfunction. More precisely, if the parameter to the built-inevalfunctionis a String , it is treated as an ECMAScriptScript . The eval code for a particular invocation ofevalis the global code portion of thatScript . Function code is source text that is parsed to supply the value of the[[ECMAScriptCode]] and[[FormalParameters]] internal slots (see
10.2 ) of an ECMAScriptfunction object . The function code of a particular ECMAScript function does not include any source text that is parsed as the function code of a nestedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression .In addition, if the source text referred to above is parsed as:
- the
FormalParameters andFunctionBody of aFunctionDeclaration orFunctionExpression , - the
FormalParameters andGeneratorBody of aGeneratorDeclaration orGeneratorExpression , - the
FormalParameters andAsyncFunctionBody of anAsyncFunctionDeclaration orAsyncFunctionExpression , or - the
FormalParameters andAsyncGeneratorBody of anAsyncGeneratorDeclaration orAsyncGeneratorExpression ,
then the
source text matched by theBindingIdentifier (if any) of that declaration or expression is also included in the function code of the corresponding function.- the
- Module code is source text that is code that is provided as a
ModuleBody . It is the code that is directly evaluated when a module is initialized. The module code of a particular module does not include any source text that is parsed as part of a nestedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction ,AsyncArrowFunction ,ClassDeclaration , orClassExpression .
Function code is generally provided as the bodies of Function Definitions (
The practical effect of including the
11.2.1 Directive Prologues and the Use Strict Directive
ADirective Prologue is the longest sequence of
AUse Strict Directive is an"use strict" or'use strict'. A
A
The
11.2.2 Strict Mode Code
An ECMAScript syntactic unit may be processed using either unrestricted or strict mode syntax and semantics (
Global code is strict mode code if it begins with aDirective Prologue that contains aUse Strict Directive .Module code is always strict mode code.- All parts of a
ClassDeclaration or aClassExpression are strict mode code. Eval code is strict mode code if it begins with aDirective Prologue that contains aUse Strict Directive or if the call toevalis adirect eval that is contained in strict mode code.Function code is strict mode code if the associatedFunctionDeclaration ,FunctionExpression ,GeneratorDeclaration ,GeneratorExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,MethodDefinition ,ArrowFunction , orAsyncArrowFunction is contained in strict mode code or if the code that produces the value of the function's[[ECMAScriptCode]] internal slot begins with aDirective Prologue that contains aUse Strict Directive .Function code that is supplied as the arguments to the built-in Function, Generator, AsyncFunction, and AsyncGeneratorconstructors is strict mode code if the last argumentis a String that when processed is aFunctionBody that begins with aDirective Prologue that contains aUse Strict Directive .
ECMAScript code that is not strict mode code is callednon-strict code.
11.2.3 Non-ECMAScript Functions
An ECMAScript implementation may support the evaluation of function
12 ECMAScript Language: Lexical Grammar
The source text of an ECMAScript
There are several situations where the identification of lexical input elements is sensitive to the syntactic grammar context that is consuming the input elements. This requires multiple
The use of multiple lexical goals ensures that there are no lexical ambiguities that would affect automatic semicolon insertion. For example, there are no syntactic grammar contexts where both a leading division or division-assignment, and a leading
a = b/hi/g.exec(c).map(d);where the first non-whitespace, non-comment code point after a
a = b / hi / g.exec(c).map(d);Syntax
12.1 Unicode Format-Control Characters
The Unicode format-control characters (i.e., the characters in category “Cf” in the Unicode Character Database such as LEFT-TO-RIGHT MARK or RIGHT-TO-LEFT MARK) are control codes used to control the formatting of a range of text in the absence of higher-level protocols for this (such as mark-up languages).
It is useful to allow format-control characters in source text to facilitate editing and display. All format control characters may be used within comments, and within string literals, template literals, and regular expression literals.
U+200C (ZERO WIDTH NON-JOINER) and U+200D (ZERO WIDTH JOINER) are format-control characters that are used to make necessary distinctions when forming words or phrases in certain languages. In
U+FEFF (ZERO WIDTH NO-BREAK SPACE) is a format-control character used primarily at the start of a text to mark it as Unicode and to allow detection of the text's encoding and byte order. <ZWNBSP> characters intended for this purpose can sometimes also appear after the start of a text, for example as a result of concatenating files. In
The special treatment of certain format-control characters outside of comments, string literals, and regular expression literals is summarized in
| Code Point | Name | Abbreviation | Usage |
|---|---|---|---|
U+200C | ZERO WIDTH NON-JOINER | <ZWNJ> | |
U+200D | ZERO WIDTH JOINER | <ZWJ> | |
U+FEFF | ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
12.2 White Space
White space code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other, but are otherwise insignificant. White space code points may occur between any two tokens and at the start or end of input. White space code points may occur within a
The ECMAScript white space code points are listed in
| Code Points | Name | Abbreviation |
|---|---|---|
U+0009 | CHARACTER TABULATION | <TAB> |
U+000B | LINE TABULATION | <VT> |
U+000C | FORM FEED (FF) | <FF> |
U+FEFF | ZERO WIDTH NO-BREAK SPACE | <ZWNBSP> |
| any code point in general category “Space_Separator” | <USP> |
U+0020 (SPACE) and U+00A0 (NO-BREAK SPACE) code points are part of <USP>.
Other than for the code points listed in
Syntax
12.3 Line Terminators
Like white space code points, line terminator code points are used to improve source text readability and to separate tokens (indivisible lexical units) from each other. However, unlike white space code points, line terminators have some influence over the behaviour of the syntactic grammar. In general, line terminators may occur between any two tokens, but there are a few places where they are forbidden by the syntactic grammar. Line terminators also affect the process of automatic semicolon insertion (
A line terminator can occur within a
Line terminators are included in the set of white space code points that are matched by the\s class in regular expressions.
The ECMAScript line terminator code points are listed in
| Code Point | Unicode Name | Abbreviation |
|---|---|---|
U+000A | LINE FEED (LF) | <LF> |
U+000D | CARRIAGE RETURN (CR) | <CR> |
U+2028 | LINE SEPARATOR | <LS> |
U+2029 | PARAGRAPH SEPARATOR | <PS> |
Only the Unicode code points in
Syntax
12.4 Comments
Comments can be either single or multi-line. Multi-line comments cannot nest.
Because a single-line comment can contain any Unicode code point except a// marker to the end of the line. However, the
Comments behave like white space and are discarded except that, if a
Syntax
A number of productions in this section are given alternative definitions in section
12.5 Hashbang Comments
Hashbang Comments are location-sensitive and like other types of comments are discarded from the stream of input elements for the syntactic grammar.
Syntax
12.6 Tokens
Syntax
The
12.7 Names and Keywords
This standard specifies specific code point additions: U+0024 (DOLLAR SIGN) and U+005F (LOW LINE) are permitted anywhere in an
Syntax
The definitions of the nonterminal
The nonterminal_ via
The sets of code points with Unicode properties “ID_Start” and “ID_Continue” include, respectively, the code points with Unicode properties “Other_ID_Start” and “Other_ID_Continue”.
12.7.1 Identifier Names
Unicode escape sequences are permitted in an\ preceding the\
Two
12.7.1.1 Static Semantics: Early Errors
- It is a Syntax Error if
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierStartChar lexical grammar production.
- It is a Syntax Error if
IdentifierCodePoint ofUnicodeEscapeSequence is not some Unicode code point matched by theIdentifierPartChar lexical grammar production.
12.7.1.2 Static Semantics: IdentifierCodePoints
The
- Letcp be
IdentifierCodePoint ofIdentifierStart . - Return «cp ».
- Letcps be
IdentifierCodePoints of the derivedIdentifierName . - Letcp be
IdentifierCodePoint ofIdentifierPart . - Return the
list-concatenation ofcps and «cp ».
12.7.1.3 Static Semantics: IdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the MV of
Hex4Digits .
- Return the code point whose numeric value is the MV of
CodePoint .
12.7.2 Keywords and Reserved Words
Akeyword is a token that matchesfixed width font, in some syntactic production. The keywords of ECMAScript includeif,while,async,await, and many others.
Areserved word is anif andwhile are reserved words.await is reserved only inside async functions and modules.async is not reserved; it can be used as a variable name or statement label without restriction.
This specification uses a combination of grammatical productions andawait andyield, are unconditionally reserved. Exceptions forawait andyield are specified in
Those that are always allowed as identifiers, and are not keywords, such as
Math,window,toString, and_;Those that are never allowed as identifiers, namely the
ReservedWord s listed below exceptawaitandyield;Those that are contextually allowed as identifiers, namely
awaitandyield;Those that are contextually disallowed as identifiers, in
strict mode code :let,static,implements,interface,package,private,protected, andpublic;Those that are always allowed as identifiers, but also appear as keywords within certain syntactic productions, at places where
Identifier is not allowed:as,async,from,get,meta,of,set, andtarget.
The termconditional keyword, orcontextual keyword, is sometimes used to refer to the keywords that fall in the last three categories, and thus can be used as identifiers in some contexts and as keywords in others.
Syntax
Per\
An\els\u{65}. The
enum is not currently used as a keyword in this specification. It is afuture reserved word, set aside for use as a keyword in future language extensions.
Similarly,implements,interface,package,private,protected, andpublic are future reserved words in
12.8 Punctuators
Syntax
12.9 Literals
12.9.1 Null Literals
Syntax
12.9.2 Boolean Literals
Syntax
12.9.3 Numeric Literals
Syntax
The
For example:3in is an error and not the two input elements3 andin.
12.9.3.1 Static Semantics: Early Errors
- It is a Syntax Error if the
source text matched by this production isstrict mode code .
12.9.3.2 Static Semantics: MV
A numeric literal stands for a value of the
- The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n), wheren is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - The MV of
DecimalLiteral :: DecimalIntegerLiteral . ExponentPart DecimalIntegerLiteral × 10e, wheree is the MV ofExponentPart . - The MV of
DecimalLiteral :: DecimalIntegerLiteral . DecimalDigits ExponentPart DecimalIntegerLiteral plus (the MV ofDecimalDigits × 10-n)) × 10e, wheren is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator ande is the MV ofExponentPart . - The MV of
DecimalLiteral :: . DecimalDigits DecimalDigits × 10-n, wheren is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - The MV of
DecimalLiteral :: . DecimalDigits ExponentPart DecimalDigits × 10e -n, wheren is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator , ande is the MV ofExponentPart . - The MV of
DecimalLiteral :: DecimalIntegerLiteral ExponentPart DecimalIntegerLiteral × 10e, wheree is the MV ofExponentPart . - The MV of
DecimalIntegerLiteral :: 0 - The MV of
DecimalIntegerLiteral :: NonZeroDigit NumericLiteralSeparator opt DecimalDigits NonZeroDigit × 10n) plus the MV ofDecimalDigits , wheren is the number of code points inDecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - The MV of
DecimalDigits :: DecimalDigits DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . - The MV of
DecimalDigits :: DecimalDigits NumericLiteralSeparator DecimalDigit DecimalDigits × 10) plus the MV ofDecimalDigit . - The MV of
ExponentPart :: ExponentIndicator SignedInteger SignedInteger . - The MV of
SignedInteger :: - DecimalDigits DecimalDigits . - The MV of
DecimalDigit :: 0 HexDigit :: 0 OctalDigit :: 0 LegacyOctalEscapeSequence :: 0 BinaryDigit :: 0 - The MV of
DecimalDigit :: 1 NonZeroDigit :: 1 HexDigit :: 1 OctalDigit :: 1 BinaryDigit :: 1 - The MV of
DecimalDigit :: 2 NonZeroDigit :: 2 HexDigit :: 2 OctalDigit :: 2 - The MV of
DecimalDigit :: 3 NonZeroDigit :: 3 HexDigit :: 3 OctalDigit :: 3 - The MV of
DecimalDigit :: 4 NonZeroDigit :: 4 HexDigit :: 4 OctalDigit :: 4 - The MV of
DecimalDigit :: 5 NonZeroDigit :: 5 HexDigit :: 5 OctalDigit :: 5 - The MV of
DecimalDigit :: 6 NonZeroDigit :: 6 HexDigit :: 6 OctalDigit :: 6 - The MV of
DecimalDigit :: 7 NonZeroDigit :: 7 HexDigit :: 7 OctalDigit :: 7 - The MV of
DecimalDigit :: 8 NonZeroDigit :: 8 NonOctalDigit :: 8 HexDigit :: 8 - The MV of
DecimalDigit :: 9 NonZeroDigit :: 9 NonOctalDigit :: 9 HexDigit :: 9 - The MV of
HexDigit :: a HexDigit :: A - The MV of
HexDigit :: b HexDigit :: B - The MV of
HexDigit :: c HexDigit :: C - The MV of
HexDigit :: d HexDigit :: D - The MV of
HexDigit :: e HexDigit :: E - The MV of
HexDigit :: f HexDigit :: F - The MV of
BinaryDigits :: BinaryDigits BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . - The MV of
BinaryDigits :: BinaryDigits NumericLiteralSeparator BinaryDigit BinaryDigits × 2) plus the MV ofBinaryDigit . - The MV of
OctalDigits :: OctalDigits OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . - The MV of
OctalDigits :: OctalDigits NumericLiteralSeparator OctalDigit OctalDigits × 8) plus the MV ofOctalDigit . - The MV of
LegacyOctalIntegerLiteral :: LegacyOctalIntegerLiteral OctalDigit LegacyOctalIntegerLiteral times 8) plus the MV ofOctalDigit . - The MV of
NonOctalDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral NonOctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofNonOctalDigit . - The MV of
NonOctalDecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral DecimalDigit NonOctalDecimalIntegerLiteral times 10) plus the MV ofDecimalDigit . - The MV of
LegacyOctalLikeDecimalIntegerLiteral :: LegacyOctalLikeDecimalIntegerLiteral OctalDigit LegacyOctalLikeDecimalIntegerLiteral times 10) plus the MV ofOctalDigit . - The MV of
HexDigits :: HexDigits HexDigit HexDigits × 16) plus the MV ofHexDigit . - The MV of
HexDigits :: HexDigits NumericLiteralSeparator HexDigit HexDigits × 16) plus the MV ofHexDigit .
12.9.3.3 Static Semantics: NumericValue
The
- Return
RoundMVResult (MV ofDecimalLiteral ).
- Return
𝔽 (MV ofNonDecimalIntegerLiteral ).
- Return
𝔽 (MV ofLegacyOctalIntegerLiteral ).
- Return the
BigInt value for the MV ofNonDecimalIntegerLiteral .
- Return
0 ℤ.
- Return the
BigInt value for the MV ofNonZeroDigit .
- Letn be the number of code points in
DecimalDigits , excluding all occurrences ofNumericLiteralSeparator . - Letmv be (the MV of
NonZeroDigit × 10n) plus the MV ofDecimalDigits . - Return
ℤ (mv).
12.9.4 String Literals
A string literal is 0 or more Unicode code points enclosed in single or double quotes. Unicode code points may also be represented by an escape sequence. All code points may appear literally in a string literal except for the closing quote code points, U+005C (REVERSE SOLIDUS), U+000D (CARRIAGE RETURN), and U+000A (LINE FEED). Any code points may appear in the form of an escape sequence. String literals evaluate to ECMAScript String values. When generating these String values Unicode code points are UTF-16 encoded as defined in
Syntax
The definition of the nonterminal
<LF> and <CR> cannot appear in a string literal, except as part of a\n or\u000A.
12.9.4.1 Static Semantics: Early Errors
- It is a Syntax Error if the
source text matched by this production isstrict mode code .
It is possible for string literals to precede a
functioninvalid() {"\7";"use strict"; }12.9.4.2 Static Semantics: SV
The
A string literal stands for a value of the
- The SV of
StringLiteral :: " " - The SV of
StringLiteral :: ' ' - The SV of
DoubleStringCharacters :: DoubleStringCharacter DoubleStringCharacters string-concatenation of the SV ofDoubleStringCharacter and the SV ofDoubleStringCharacters . - The SV of
SingleStringCharacters :: SingleStringCharacter SingleStringCharacters string-concatenation of the SV ofSingleStringCharacter and the SV ofSingleStringCharacters . - The SV of
DoubleStringCharacter :: SourceCharacter but not one of " or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . - The SV of
DoubleStringCharacter :: <LS> - The SV of
DoubleStringCharacter :: <PS> - The SV of
DoubleStringCharacter :: LineContinuation - The SV of
SingleStringCharacter :: SourceCharacter but not one of ' or\ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . - The SV of
SingleStringCharacter :: <LS> - The SV of
SingleStringCharacter :: <PS> - The SV of
SingleStringCharacter :: LineContinuation - The SV of
EscapeSequence :: 0 - The SV of
CharacterEscapeSequence :: SingleEscapeCharacter SingleEscapeCharacter according toTable 38 .
| Escape Sequence | Code Unit Value | Unicode Character Name | Symbol |
|---|---|---|---|
\b | 0x0008 | BACKSPACE | <BS> |
\t | 0x0009 | CHARACTER TABULATION | <HT> |
\n | 0x000A | LINE FEED (LF) | <LF> |
\v | 0x000B | LINE TABULATION | <VT> |
\f | 0x000C | FORM FEED (FF) | <FF> |
\r | 0x000D | CARRIAGE RETURN (CR) | <CR> |
\" | 0x0022 | QUOTATION MARK | " |
\' | 0x0027 | APOSTROPHE | ' |
\\ | 0x005C | REVERSE SOLIDUS | \ |
- The SV of
NonEscapeCharacter :: SourceCharacter but not one of EscapeCharacter orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . - The SV of
EscapeSequence :: LegacyOctalEscapeSequence LegacyOctalEscapeSequence . - The SV of
NonOctalDecimalEscapeSequence :: 8 - The SV of
NonOctalDecimalEscapeSequence :: 9 - The SV of
HexEscapeSequence :: x HexDigit HexDigit HexEscapeSequence . - The SV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit Hex4Digits . - The SV of
UnicodeEscapeSequence :: u{ CodePoint } UTF16EncodeCodePoint on the MV ofCodePoint . - The SV of
TemplateEscapeSequence :: 0
12.9.4.3 Static Semantics: MV
- The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit ZeroToThree ) plus the MV ofOctalDigit . - The MV of
LegacyOctalEscapeSequence :: FourToSeven OctalDigit FourToSeven ) plus the MV ofOctalDigit . - The MV of
LegacyOctalEscapeSequence :: ZeroToThree OctalDigit OctalDigit ZeroToThree ) plus (8 times the MV of the firstOctalDigit ) plus the MV of the secondOctalDigit . - The MV of
ZeroToThree :: 0 - The MV of
ZeroToThree :: 1 - The MV of
ZeroToThree :: 2 - The MV of
ZeroToThree :: 3 - The MV of
FourToSeven :: 4 - The MV of
FourToSeven :: 5 - The MV of
FourToSeven :: 6 - The MV of
FourToSeven :: 7 - The MV of
HexEscapeSequence :: x HexDigit HexDigit HexDigit ) plus the MV of the secondHexDigit . - The MV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit HexDigit ) plus (0x100 × the MV of the secondHexDigit ) plus (0x10 × the MV of the thirdHexDigit ) plus the MV of the fourthHexDigit .
12.9.5 Regular Expression Literals
A regular expression literal is an input element that is converted to a RegExp object (see=== to each other even if the two literals' contents are identical. A RegExp object may also be created at runtime bynew RegExp or calling the RegExp
The productions below describe the syntax for a regular expression literal and are used by the input element scanner to find the end of the regular expression literal. The source text comprising the
An implementation may extend the ECMAScript Regular Expression grammar defined in
Syntax
Regular expression literals may not be empty; instead of representing an empty regular expression literal, the code unit sequence// starts a single-line comment. To specify an empty regular expression, use:/(?:)/.
12.9.5.1 Static Semantics: BodyText
The
- Return the source text that was recognized as
RegularExpressionBody .
12.9.5.2 Static Semantics: FlagText
The
- Return the source text that was recognized as
RegularExpressionFlags .
12.9.6 Template Literal Lexical Components
Syntax
12.9.6.1 Static Semantics: TV
The
- The TV of
NoSubstitutionTemplate :: ` ` - The TV of
TemplateHead :: ` ${ - The TV of
TemplateMiddle :: } ${ - The TV of
TemplateTail :: } ` - The TV of
TemplateCharacters :: TemplateCharacter TemplateCharacters undefined if the TV ofTemplateCharacter isundefined or the TV ofTemplateCharacters isundefined . Otherwise, it is thestring-concatenation of the TV ofTemplateCharacter and the TV ofTemplateCharacters . - The TV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . - The TV of
TemplateCharacter :: $ - The TV of
TemplateCharacter :: \ TemplateEscapeSequence SV ofTemplateEscapeSequence . - The TV of
TemplateCharacter :: \ NotEscapeSequence undefined . - The TV of
TemplateCharacter :: LineTerminatorSequence TRV ofLineTerminatorSequence . - The TV of
LineContinuation :: \ LineTerminatorSequence
12.9.6.2 Static Semantics: TRV
The
- The TRV of
NoSubstitutionTemplate :: ` ` - The TRV of
TemplateHead :: ` ${ - The TRV of
TemplateMiddle :: } ${ - The TRV of
TemplateTail :: } ` - The TRV of
TemplateCharacters :: TemplateCharacter TemplateCharacters string-concatenation of the TRV ofTemplateCharacter and the TRV ofTemplateCharacters . - The TRV of
TemplateCharacter :: SourceCharacter but not one of ` or\ or$ orLineTerminator UTF16EncodeCodePoint on the code point matched bySourceCharacter . - The TRV of
TemplateCharacter :: $ - The TRV of
TemplateCharacter :: \ TemplateEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofTemplateEscapeSequence . - The TRV of
TemplateCharacter :: \ NotEscapeSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofNotEscapeSequence . - The TRV of
TemplateEscapeSequence :: 0 - The TRV of
NotEscapeSequence :: 0 DecimalDigit string-concatenation of the code unit 0x0030 (DIGIT ZERO) and the TRV ofDecimalDigit . - The TRV of
NotEscapeSequence :: x [lookahead ∉ HexDigit ] - The TRV of
NotEscapeSequence :: x HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X) and the TRV ofHexDigit . - The TRV of
NotEscapeSequence :: u [lookahead ∉ HexDigit ][lookahead ≠ { ] - The TRV of
NotEscapeSequence :: u HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHexDigit . - The TRV of
NotEscapeSequence :: u HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . - The TRV of
NotEscapeSequence :: u HexDigit HexDigit HexDigit [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the TRV of the firstHexDigit , the TRV of the secondHexDigit , and the TRV of the thirdHexDigit . - The TRV of
NotEscapeSequence :: u { [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the code unit 0x007B (LEFT CURLY BRACKET). - The TRV of
NotEscapeSequence :: u { NotCodePoint [lookahead ∉ HexDigit ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofNotCodePoint . - The TRV of
NotEscapeSequence :: u { CodePoint [lookahead ∉ HexDigit ][lookahead ≠ } ]string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), and the TRV ofCodePoint . - The TRV of
DecimalDigit :: one of 0 1 2 3 4 5 6 7 8 9 UTF16EncodeCodePoint on the single code point matched by this production. - The TRV of
CharacterEscapeSequence :: NonEscapeCharacter SV ofNonEscapeCharacter . - The TRV of
SingleEscapeCharacter :: one of ' " \ b f n r t v UTF16EncodeCodePoint on the single code point matched by this production. - The TRV of
HexEscapeSequence :: x HexDigit HexDigit string-concatenation of the code unit 0x0078 (LATIN SMALL LETTER X), the TRV of the firstHexDigit , and the TRV of the secondHexDigit . - The TRV of
UnicodeEscapeSequence :: u Hex4Digits string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U) and the TRV ofHex4Digits . - The TRV of
UnicodeEscapeSequence :: u{ CodePoint } string-concatenation of the code unit 0x0075 (LATIN SMALL LETTER U), the code unit 0x007B (LEFT CURLY BRACKET), the TRV ofCodePoint , and the code unit 0x007D (RIGHT CURLY BRACKET). - The TRV of
Hex4Digits :: HexDigit HexDigit HexDigit HexDigit string-concatenation of the TRV of the firstHexDigit , the TRV of the secondHexDigit , the TRV of the thirdHexDigit , and the TRV of the fourthHexDigit . - The TRV of
HexDigits :: HexDigits HexDigit string-concatenation of the TRV ofHexDigits and the TRV ofHexDigit . - The TRV of
HexDigit :: one of 0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F UTF16EncodeCodePoint on the single code point matched by this production. - The TRV of
LineContinuation :: \ LineTerminatorSequence string-concatenation of the code unit 0x005C (REVERSE SOLIDUS) and the TRV ofLineTerminatorSequence . - The TRV of
LineTerminatorSequence :: <LF> - The TRV of
LineTerminatorSequence :: <CR> - The TRV of
LineTerminatorSequence :: <LS> - The TRV of
LineTerminatorSequence :: <PS> - The TRV of
LineTerminatorSequence :: <CR> <LF>
12.10 Automatic Semicolon Insertion
Most ECMAScript statements and declarations must be terminated with a semicolon. Such semicolons may always appear explicitly in the source text. For convenience, however, such semicolons may be omitted from the source text in certain situations. These situations are described by saying that semicolons are automatically inserted into the source code token stream in those situations.
12.10.1 Rules of Automatic Semicolon Insertion
In the following rules, “token” means the actual recognized lexical token determined using the current lexical
There are three basic rules of semicolon insertion:
When, as the source text is parsed from left to right, a token (called theoffending token) is encountered that is not allowed by any production of the grammar, then a semicolon is automatically inserted before the offending token if one or more of the following conditions is true:
- The offending token is separated from the previous token by at least one
LineTerminator . - The offending token is
}. - The previous token is
)and the inserted semicolon would then be parsed as the terminating semicolon of a do-while statement (14.7.2 ).
- The offending token is separated from the previous token by at least one
- When, as the source text is parsed from left to right, the end of the input stream of tokens is encountered and the parser is unable to parse the input token stream as a single instance of the goal nonterminal, then a semicolon is automatically inserted at the end of the input stream.
- When, as the source text is parsed from left to right, a token is encountered that is allowed by some production of the grammar, but the production is arestricted production and the token would be the first token for a terminal or nonterminal immediately following the annotation “[no
LineTerminator here]” within the restricted production (and therefore such a token is called a restricted token), and the restricted token is separated from the previous token by at least oneLineTerminator , then a semicolon is automatically inserted before the restricted token.
However, there is an additional overriding condition on the preceding rules: a semicolon is never inserted automatically if the semicolon would then be parsed as an empty statement or if that semicolon would become one of the two semicolons in the header of afor statement (see
The following are the only restricted productions in the grammar:
The practical effect of these restricted productions is as follows:
- When a
++or--token is encountered where the parser would treat it as a postfix operator, and at least oneLineTerminator occurred between the preceding token and the++or--token, then a semicolon is automatically inserted before the++or--token. - When a
continue,break,return,throw, oryieldtoken is encountered and aLineTerminator is encountered before the next token, a semicolon is automatically inserted after thecontinue,break,return,throw, oryieldtoken. - When arrow function parameter(s) are followed by a
LineTerminator before a=>token, a semicolon is automatically inserted and the punctuator causes a syntax error. - When an
asynctoken is followed by aLineTerminator before afunctionorIdentifierName or(token, a semicolon is automatically inserted and theasynctoken is not treated as part of the same expression or class element as the following tokens. - When an
asynctoken is followed by aLineTerminator before a*token, a semicolon is automatically inserted and the punctuator causes a syntax error.
The resulting practical advice to ECMAScript programmers is:
- A postfix
++or--operator should be on the same line as its operand. - An
Expression in areturnorthrowstatement or anAssignmentExpression in ayieldexpression should start on the same line as thereturn,throw, oryieldtoken. - A
LabelIdentifier in abreakorcontinuestatement should be on the same line as thebreakorcontinuetoken. - The end of an arrow function's parameter(s) and its
=>should be on the same line. - The
asynctoken preceding an asynchronous function or method should be on the same line as the immediately following token.
12.10.2 Examples of Automatic Semicolon Insertion
This section is non-normative.The source
{12 }3is not a valid sentence in the ECMAScript grammar, even with the automatic semicolon insertion rules. In contrast, the source
{12 }3is also not a valid ECMAScript sentence, but is transformed by automatic semicolon insertion into the following:
{1;2 ;}3;which is a valid ECMAScript sentence.
The source
for (a; b)is not a valid ECMAScript sentence and is not altered by automatic semicolon insertion because the semicolon is needed for the header of afor statement. Automatic semicolon insertion never inserts one of the two semicolons in the header of afor statement.
The source
returna + bis transformed by automatic semicolon insertion into the following:
return;a + b;The expressiona + b is not treated as a value to be returned by thereturn statement, because areturn.
The source
a = b++cis transformed by automatic semicolon insertion into the following:
a = b;++c;The token++ is not treated as a postfix operator applying to the variableb, because ab and++.
The source
if (a > b)else c = dis not a valid ECMAScript sentence and is not altered by automatic semicolon insertion before theelse token, even though no production of the grammar applies at that point, because an automatically inserted semicolon would then be parsed as an empty statement.
The source
a = b + c(d + e).print()isnot transformed by automatic semicolon insertion, because the parenthesized expression that begins the second line can be interpreted as an argument list for a function call:
a = b +c(d + e).print()In the circumstance that an assignment statement must begin with a left parenthesis, it is a good idea for the programmer to provide an explicit semicolon at the end of the preceding statement rather than to rely on automatic semicolon insertion.
12.10.3 Interesting Cases of Automatic Semicolon Insertion
This section is non-normative.ECMAScript programs can be written in a style with very few semicolons by relying on automatic semicolon insertion. As described above, semicolons are not inserted at every newline, and automatic semicolon insertion can depend on multiple tokens across line terminators.
As new syntactic features are added to ECMAScript, additional grammar productions could be added that cause lines relying on automatic semicolon insertion preceding them to change grammar productions when parsed.
For the purposes of this section, a case of automatic semicolon insertion is considered interesting if it is a place where a semicolon may or may not be inserted, depending on the source text which precedes it. The rest of this section describes a number of interesting cases of automatic semicolon insertion in this version of ECMAScript.
12.10.3.1 Interesting Cases of Automatic Semicolon Insertion in Statement Lists
In a
- An opening parenthesis (
(). Without a semicolon, the two lines together are treated as aCallExpression . - An opening square bracket (
[). Without a semicolon, the two lines together are treated as property access, rather than anArrayLiteral orArrayAssignmentPattern . - A template literal (
`). Without a semicolon, the two lines together are interpreted as a tagged Template (13.3.11 ), with the previous expression as theMemberExpression . - Unary
+or-. Without a semicolon, the two lines together are interpreted as a usage of the corresponding binary operator. - A RegExp literal. Without a semicolon, the two lines together may be parsed instead as the
/MultiplicativeOperator , for example if the RegExp has flags.
12.10.3.2 Cases of Automatic Semicolon Insertion and “[noLineTerminator here]”
This section is non-normative.ECMAScript contains grammar productions which include “[no
The rest of this section describes a number of productions using “[no
12.10.3.2.1 List of Grammar Productions with Optional Operands and “[noLineTerminator here]”
UpdateExpression .ContinueStatement .BreakStatement .ReturnStatement .YieldExpression .- Async Function Definitions (
15.8 ) with relation to Function Definitions (15.2 )
13 ECMAScript Language: Expressions
13.1 Identifiers
Syntax
yield andawait are permitted as
letawait0;13.1.1 Static Semantics: Early Errors
- It is a Syntax Error if the
source text matched by this production is contained instrict mode code and theStringValue ofIdentifier is either"arguments" or"eval" .
- It is a Syntax Error if the
source text matched by this production is contained instrict mode code .
- It is a Syntax Error if the
goal symbol of the syntactic grammar isModule .
- It is a Syntax Error if this production has a[Yield] parameter.
- It is a Syntax Error if this production has an[Await] parameter.
- It is a Syntax Error if this production has a[Yield] parameter and
StringValue ofIdentifier is"yield" . - It is a Syntax Error if this production has an[Await] parameter and
StringValue ofIdentifier is"await" .
- It is a Syntax Error if this phrase is contained in
strict mode code and theStringValue ofIdentifierName is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" ,"static" , or"yield" . - It is a Syntax Error if the
goal symbol of the syntactic grammar isModule and theStringValue ofIdentifierName is"await" . - It is a Syntax Error if the
StringValue ofIdentifierName is theStringValue of anyReservedWord except foryieldorawait.
13.1.2 Static Semantics: StringValue
The
- LetidTextUnescaped be
IdentifierCodePoints ofIdentifierName . - Return
CodePointsToString (idTextUnescaped).
- Return
"yield" .
- Return
"await" .
- Return the
StringValue ofIdentifierName .
- Return the
string-concatenation of 0x0023 (NUMBER SIGN) and theStringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
13.1.3 Runtime Semantics: Evaluation
- Return ?
ResolveBinding (StringValue ofIdentifier ).
- Return ?
ResolveBinding ("yield" ).
- Return ?
ResolveBinding ("await" ).
The result of evaluating an
Inyield may be used as an identifier. Evaluating theyield as if it was an
13.2 Primary Expression
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.2.1 Thethis Keyword
13.2.1.1 Runtime Semantics: Evaluation
- Return ?
ResolveThisBinding ().
13.2.2 Identifier Reference
See
13.2.3 Literals
Syntax
13.2.3.1 Runtime Semantics: Evaluation
- Return
null .
- If
BooleanLiteral is the tokenfalse, returnfalse . - If
BooleanLiteral is the tokentrue, returntrue .
- Return the
NumericValue ofNumericLiteral as defined in12.9.3 .
- Return the
SV ofStringLiteral as defined in12.9.4.2 .
13.2.4 Array Initializer
An
Array elements may be elided at the beginning, middle or end of the element list. Whenever a comma in the element list is not preceded by an
Syntax
13.2.4.1 Runtime Semantics: ArrayAccumulation
The
- Return ?
ArrayAccumulation ofElision with argumentsarray and (nextIndex + 1).
- If
Elision is present, then- SetnextIndex to ?
ArrayAccumulation ofElision with argumentsarray andnextIndex.
- SetnextIndex to ?
- LetinitResult be ?
Evaluation ofAssignmentExpression . - LetinitValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)),initValue). - ReturnnextIndex + 1.
- If
Elision is present, then- SetnextIndex to ?
ArrayAccumulation ofElision with argumentsarray andnextIndex.
- SetnextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with argumentsarray andnextIndex.
- SetnextIndex to ?
ArrayAccumulation ofElementList with argumentsarray andnextIndex. - If
Elision is present, then- SetnextIndex to ?
ArrayAccumulation ofElision with argumentsarray andnextIndex.
- SetnextIndex to ?
- LetinitResult be ?
Evaluation ofAssignmentExpression . - LetinitValue be ?
GetValue (initResult). - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)),initValue). - ReturnnextIndex + 1.
- SetnextIndex to ?
ArrayAccumulation ofElementList with argumentsarray andnextIndex. - If
Elision is present, then- SetnextIndex to ?
ArrayAccumulation ofElision with argumentsarray andnextIndex.
- SetnextIndex to ?
- Return ?
ArrayAccumulation ofSpreadElement with argumentsarray andnextIndex.
- LetspreadRef be ?
Evaluation ofAssignmentExpression . - LetspreadObj be ?
GetValue (spreadRef). - LetiteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returnnextIndex. - Perform !
CreateDataPropertyOrThrow (array, !ToString (𝔽 (nextIndex)),next). - SetnextIndex tonextIndex + 1.
- Letnext be ?
13.2.4.2 Runtime Semantics: Evaluation
- Letarray be !
ArrayCreate (0). - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with argumentsarray and 0.
- Perform ?
- Returnarray.
- Letarray be !
ArrayCreate (0). - Perform ?
ArrayAccumulation ofElementList with argumentsarray and 0. - Returnarray.
- Letarray be !
ArrayCreate (0). - LetnextIndex be ?
ArrayAccumulation ofElementList with argumentsarray and 0. - If
Elision is present, then- Perform ?
ArrayAccumulation ofElision with argumentsarray andnextIndex.
- Perform ?
- Returnarray.
13.2.5 Object Initializer
An object initializer is an expression describing the initialization of an Object, written in a form resembling a literal. It is a list of zero or more pairs of
Syntax
In certain contexts,
13.2.5.1 Static Semantics: Early Errors
- It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . - It is a Syntax Error if
PrivateBoundIdentifiers ofMethodDefinition is not empty.
In addition to describing an actual object initializer the
- It is a Syntax Error if any source text is matched by this production.
This production exists so that
- It is a Syntax Error if
PropertyNameList ofPropertyDefinitionList contains any duplicate entries for"__proto__" and at least two of those entries were obtained from productions of the formPropertyDefinition : PropertyName : AssignmentExpression ObjectLiteral is contained within aScript that is being parsed for JSON.parse (see step4 ofJSON.parse ).
The
13.2.5.2 Static Semantics: IsComputedPropertyKey
The
- Return
false .
- Return
true .
13.2.5.3 Static Semantics: PropertyNameList
The
- LetpropName be
PropName ofPropertyDefinition . - IfpropName is
empty , return a new emptyList . - Return «propName ».
- Letlist be
PropertyNameList ofPropertyDefinitionList . - LetpropName be
PropName ofPropertyDefinition . - IfpropName is
empty , returnlist. - Return the
list-concatenation oflist and «propName ».
13.2.5.4 Runtime Semantics: Evaluation
- Letobj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argumentobj. - Returnobj.
- Return
StringValue ofIdentifierName .
- Return the
SV ofStringLiteral .
- Letnbr be the
NumericValue ofNumericLiteral . - Return !
ToString (nbr).
- LetexprValue be ?
Evaluation ofAssignmentExpression . - LetpropName be ?
GetValue (exprValue). - Return ?
ToPropertyKey (propName).
13.2.5.5 Runtime Semantics: PropertyDefinitionEvaluation
The
- Perform ?
PropertyDefinitionEvaluation ofPropertyDefinitionList with argumentobject. - Perform ?
PropertyDefinitionEvaluation ofPropertyDefinition with argumentobject. - Return
unused .
- LetexprValue be ?
Evaluation ofAssignmentExpression . - LetfromValue be ?
GetValue (exprValue). - LetexcludedNames be a new empty
List . - Perform ?
CopyDataProperties (object,fromValue,excludedNames). - Return
unused .
- LetpropName be
StringValue ofIdentifierReference . - LetexprValue be ?
Evaluation ofIdentifierReference . - LetpropValue be ?
GetValue (exprValue). Assert :object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object,propName,propValue). - Return
unused .
- LetpropKey be ?
Evaluation ofPropertyName . - If this
PropertyDefinition is contained within aScript that is being evaluated for JSON.parse (see step7 ofJSON.parse ), then- LetisProtoSetter be
false .
- LetisProtoSetter be
- Else ifpropKey is
"__proto__" andIsComputedPropertyKey ofPropertyName isfalse , then- LetisProtoSetter be
true .
- LetisProtoSetter be
- Else,
- LetisProtoSetter be
false .
- LetisProtoSetter be
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andisProtoSetter isfalse , then- LetpropValue be ?
NamedEvaluation ofAssignmentExpression with argumentpropKey.
- LetpropValue be ?
- Else,
- LetexprValueRef be ?
Evaluation ofAssignmentExpression . - LetpropValue be ?
GetValue (exprValueRef).
- LetexprValueRef be ?
- IfisProtoSetter is
true , then- IfpropValue
is an Object orpropValue isnull , then- Perform ! object.[[SetPrototypeOf]](propValue).
- Return
unused .
- IfpropValue
Assert :object is an ordinary, extensible object with no non-configurable properties.- Perform !
CreateDataPropertyOrThrow (object,propKey,propValue). - Return
unused .
- Perform ?
MethodDefinitionEvaluation ofMethodDefinition with argumentsobject andtrue . - Return
unused .
13.2.6 Function Defining Expressions
See
See
See
13.2.7 Regular Expression Literals
Syntax
See
13.2.7.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsValidRegularExpressionLiteral (RegularExpressionLiteral ) isfalse .
13.2.7.2 Static Semantics: IsValidRegularExpressionLiteral (literal )
The abstract operation IsValidRegularExpressionLiteral takes argumentliteral (a
- Letflags be
FlagText ofliteral. - Ifflags contains any code points other than
d,g,i,m,s,u,v, ory, or ifflags contains any code point more than once, returnfalse . - Ifflags contains
u, letu betrue ; else letu befalse . - Ifflags contains
v, letv betrue ; else letv befalse . - LetpatternText be
BodyText ofliteral. - Ifu is
false andv isfalse , then- LetstringValue be
CodePointsToString (patternText). - SetpatternText to the sequence of code points resulting from interpreting each of the 16-bit elements ofstringValue as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- LetstringValue be
- LetparseResult be
ParsePattern (patternText,u,v). - IfparseResult is a
Parse Node , returntrue ; else returnfalse .
13.2.7.3 Runtime Semantics: Evaluation
- Letpattern be
CodePointsToString (BodyText ofRegularExpressionLiteral ). - Letflags be
CodePointsToString (FlagText ofRegularExpressionLiteral ). - Return !
RegExpCreate (pattern,flags).
13.2.8 Template Literals
Syntax
13.2.8.1 Static Semantics: Early Errors
- It is a Syntax Error if the[Tagged] parameter was not set and
NoSubstitutionTemplate Contains NotEscapeSequence .
- It is a Syntax Error if the number of elements in the result of
TemplateStrings ofTemplateLiteral with argumentfalse is greater than or equal to 232.
- It is a Syntax Error if the[Tagged] parameter was not set and
TemplateHead Contains NotEscapeSequence .
- It is a Syntax Error if the[Tagged] parameter was not set and
TemplateTail Contains NotEscapeSequence .
- It is a Syntax Error if the[Tagged] parameter was not set and
TemplateMiddle Contains NotEscapeSequence .
13.2.8.2 Static Semantics: TemplateStrings
The
- Return «
TemplateString (NoSubstitutionTemplate ,raw) ».
- Lethead be «
TemplateString (TemplateHead ,raw) ». - Lettail be
TemplateStrings ofTemplateSpans with argumentraw. - Return the
list-concatenation ofhead andtail.
- Return «
TemplateString (TemplateTail ,raw) ».
- Letmiddle be
TemplateStrings ofTemplateMiddleList with argumentraw. - Lettail be «
TemplateString (TemplateTail ,raw) ». - Return the
list-concatenation ofmiddle andtail.
- Return «
TemplateString (TemplateMiddle ,raw) ».
- Letfront be
TemplateStrings ofTemplateMiddleList with argumentraw. - Letlast be «
TemplateString (TemplateMiddle ,raw) ». - Return the
list-concatenation offront andlast.
13.2.8.3 Static Semantics: TemplateString (templateToken,raw )
The abstract operation TemplateString takes argumentstemplateToken (a
This operation returns
13.2.8.4 GetTemplateObject (templateLiteral )
The abstract operation GetTemplateObject takes argumenttemplateLiteral (a
- Letrealm be
the current Realm Record . - LettemplateRegistry berealm.[[TemplateMap]].
- For each elemente oftemplateRegistry, do
- Ife.[[Site]] is
the same Parse Node astemplateLiteral, then- Returne.[[Array]].
- Ife.[[Site]] is
- LetrawStrings be
TemplateStrings oftemplateLiteral with argumenttrue . Assert :rawStrings is aList of Strings.- LetcookedStrings be
TemplateStrings oftemplateLiteral with argumentfalse . - Letcount be the number of elements in the
List cookedStrings. Assert :count ≤ 232 - 1.- Lettemplate be !
ArrayCreate (count). - LetrawObj be !
ArrayCreate (count). - Letindex be 0.
- Repeat, whileindex <count,
- Letprop be !
ToString (𝔽 (index)). - LetcookedValue becookedStrings[index].
- Perform !
DefinePropertyOrThrow (template,prop, PropertyDescriptor {[[Value]]:cookedValue,[[Writable]]:false ,[[Enumerable]]:true ,[[Configurable]]:false }). - LetrawValue be the String valuerawStrings[index].
- Perform !
DefinePropertyOrThrow (rawObj,prop, PropertyDescriptor {[[Value]]:rawValue,[[Writable]]:false ,[[Enumerable]]:true ,[[Configurable]]:false }). - Setindex toindex + 1.
- Letprop be !
- Perform !
SetIntegrityLevel (rawObj,frozen ). - Perform !
DefinePropertyOrThrow (template,"raw" , PropertyDescriptor {[[Value]]:rawObj,[[Writable]]:false ,[[Enumerable]]:false ,[[Configurable]]:false }). - Perform !
SetIntegrityLevel (template,frozen ). - Append the
Record {[[Site]]:templateLiteral,[[Array]]:template } torealm.[[TemplateMap]]. - Returntemplate.
The creation of a template object cannot result in an
Each
Future editions of this specification may define additional non-enumerable properties of template objects.
13.2.8.5 Runtime Semantics: SubstitutionEvaluation
The
- Return a new empty
List .
- Return ?
SubstitutionEvaluation ofTemplateMiddleList .
- LetsubRef be ?
Evaluation ofExpression . - Letsub be ?
GetValue (subRef). - Return «sub ».
- Letpreceding be ?
SubstitutionEvaluation ofTemplateMiddleList . - LetnextRef be ?
Evaluation ofExpression . - Letnext be ?
GetValue (nextRef). - Return the
list-concatenation ofpreceding and «next ».
13.2.8.6 Runtime Semantics: Evaluation
- Return the
TV ofNoSubstitutionTemplate as defined in12.9.6 .
- Lethead be the
TV ofTemplateHead as defined in12.9.6 . - LetsubRef be ?
Evaluation ofExpression . - Letsub be ?
GetValue (subRef). - Letmiddle be ?
ToString (sub). - Lettail be ?
Evaluation ofTemplateSpans . - Return the
string-concatenation ofhead,middle, andtail.
The string conversion semantics applied to theString.prototype.concat rather than the+ operator.
- Return the
TV ofTemplateTail as defined in12.9.6 .
- Lethead be ?
Evaluation ofTemplateMiddleList . - Lettail be the
TV ofTemplateTail as defined in12.9.6 . - Return the
string-concatenation ofhead andtail.
- Lethead be the
TV ofTemplateMiddle as defined in12.9.6 . - LetsubRef be ?
Evaluation ofExpression . - Letsub be ?
GetValue (subRef). - Letmiddle be ?
ToString (sub). - Return the
string-concatenation ofhead andmiddle.
The string conversion semantics applied to theString.prototype.concat rather than the+ operator.
- Letrest be ?
Evaluation ofTemplateMiddleList . - Letmiddle be the
TV ofTemplateMiddle as defined in12.9.6 . - LetsubRef be ?
Evaluation ofExpression . - Letsub be ?
GetValue (subRef). - Letlast be ?
ToString (sub). - Return the
string-concatenation ofrest,middle, andlast.
The string conversion semantics applied to theString.prototype.concat rather than the+ operator.
13.2.9 The Grouping Operator
13.2.9.1 Static Semantics: Early Errors
13.2.9.2 Runtime Semantics: Evaluation
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return ?
Evaluation ofexpr.
- Return ?
Evaluation ofExpression . This may be of type Reference.
This algorithm does not applydelete andtypeof may be applied to parenthesized expressions.
13.3 Left-Hand-Side Expressions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
13.3.1 Static Semantics
13.3.1.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
This production exists in order to prevent automatic semicolon insertion rules (
a?.b`c`so that it would be interpreted as two valid statements. The purpose is to maintain consistency with similar code without optional chaining:
a.b`c`which is a valid statement and where automatic semicolon insertion does not apply.
- It is a Syntax Error if the syntactic
goal symbol is notModule .
13.3.2 Property Accessors
Properties are accessed by name, using either the dot notation:
or the bracket notation:
The dot notation is explained by the following syntactic conversion:
is identical in its behaviour to
and similarly
is identical in its behaviour to
where <identifier-name-string> is the result of evaluating
13.3.2.1 Runtime Semantics: Evaluation
- LetbaseReference be ?
Evaluation ofMemberExpression . - LetbaseValue be ?
GetValue (baseReference). - If the
source text matched by thisMemberExpression isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression ,strict).
- LetbaseReference be ?
Evaluation ofMemberExpression . - LetbaseValue be ?
GetValue (baseReference). - If the
source text matched by thisMemberExpression isstrict mode code , letstrict betrue ; else letstrict befalse . - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName ,strict).
- LetbaseReference be ?
Evaluation ofMemberExpression . - LetbaseValue be ?
GetValue (baseReference). - LetfieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue,fieldNameString).
- LetbaseReference be ?
Evaluation ofCallExpression . - LetbaseValue be ?
GetValue (baseReference). - If the
source text matched by thisCallExpression isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression ,strict).
- LetbaseReference be ?
Evaluation ofCallExpression . - LetbaseValue be ?
GetValue (baseReference). - If the
source text matched by thisCallExpression isstrict mode code , letstrict betrue ; else letstrict befalse . - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName ,strict).
- LetbaseReference be ?
Evaluation ofCallExpression . - LetbaseValue be ?
GetValue (baseReference). - LetfieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue,fieldNameString).
13.3.3 EvaluatePropertyAccessWithExpressionKey (baseValue,expression,strict )
The abstract operation EvaluatePropertyAccessWithExpressionKey takes argumentsbaseValue (an
- LetpropertyNameReference be ?
Evaluation ofexpression. - LetpropertyNameValue be ?
GetValue (propertyNameReference). - LetpropertyKey be ?
ToPropertyKey (propertyNameValue). - Return the
Reference Record {[[Base]]:baseValue,[[ReferencedName]]:propertyKey,[[Strict]]:strict,[[ThisValue]]:empty }.
13.3.4 EvaluatePropertyAccessWithIdentifierKey (baseValue,identifierName,strict )
The abstract operation EvaluatePropertyAccessWithIdentifierKey takes argumentsbaseValue (an
- LetpropertyNameString be
StringValue ofidentifierName. - Return the
Reference Record {[[Base]]:baseValue,[[ReferencedName]]:propertyNameString,[[Strict]]:strict,[[ThisValue]]:empty }.
13.3.5 Thenew Operator
13.3.5.1 Runtime Semantics: Evaluation
- Return ?
EvaluateNew (NewExpression ,empty ).
- Return ?
EvaluateNew (MemberExpression ,Arguments ).
13.3.5.1.1 EvaluateNew (constructExpr,arguments )
The abstract operation EvaluateNew takes argumentsconstructExpr (a
- Letref be ?
Evaluation ofconstructExpr. - Letconstructor be ?
GetValue (ref). - Ifarguments is
empty , then- LetargList be a new empty
List .
- LetargList be a new empty
- Else,
- LetargList be ?
ArgumentListEvaluation ofarguments.
- LetargList be ?
- If
IsConstructor (constructor) isfalse , throw aTypeError exception. - Return ?
Construct (constructor,argList).
13.3.6 Function Calls
13.3.6.1 Runtime Semantics: Evaluation
- Letexpr be the
CallMemberExpression that iscovered byCoverCallExpressionAndAsyncArrowHead . - LetmemberExpr be the
MemberExpression ofexpr. - Letarguments be the
Arguments ofexpr. - Letref be ?
Evaluation ofmemberExpr. - Letfunc be ?
GetValue (ref). - Ifref is a
Reference Record ,IsPropertyReference (ref) isfalse , andref.[[ReferencedName]] is"eval" , then- If
SameValue (func,%eval% ) istrue , then- LetargList be ?
ArgumentListEvaluation ofarguments. - IfargList has no elements, return
undefined . - LetevalArg be the first element ofargList.
- If the
source text matched by thisCallExpression isstrict mode code , letstrictCaller betrue . Otherwise letstrictCaller befalse . - Return ?
PerformEval (evalArg,strictCaller,true ).
- LetargList be ?
- If
- LetthisCall be this
CallExpression . - LettailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func,ref,arguments,tailCall).
A
- Letref be ?
Evaluation ofCallExpression . - Letfunc be ?
GetValue (ref). - LetthisCall be this
CallExpression . - LettailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (func,ref,Arguments ,tailCall).
13.3.6.2 EvaluateCall (func,ref,arguments,tailPosition )
The abstract operation EvaluateCall takes argumentsfunc (an
- Ifref is a
Reference Record , then- If
IsPropertyReference (ref) istrue , then- LetthisValue be
GetThisValue (ref).
- LetthisValue be
- Else,
- LetrefEnv beref.[[Base]].
Assert :refEnv is anEnvironment Record .- LetthisValue berefEnv.WithBaseObject().
- If
- Else,
- LetthisValue be
undefined .
- LetthisValue be
- LetargList be ?
ArgumentListEvaluation ofarguments. - Iffunc
is not an Object , throw aTypeError exception. - If
IsCallable (func) isfalse , throw aTypeError exception. - IftailPosition is
true , performPrepareForTailCall (). - Return ?
Call (func,thisValue,argList).
13.3.7 Thesuper Keyword
13.3.7.1 Runtime Semantics: Evaluation
- Letenv be
GetThisEnvironment (). - LetactualThis be ? env.GetThisBinding().
- LetpropertyNameReference be ?
Evaluation ofExpression . - LetpropertyNameValue be ?
GetValue (propertyNameReference). - LetpropertyKey be ?
ToPropertyKey (propertyNameValue). - If the
source text matched by thisSuperProperty isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
MakeSuperPropertyReference (actualThis,propertyKey,strict).
- Letenv be
GetThisEnvironment (). - LetactualThis be ? env.GetThisBinding().
- LetpropertyKey be
StringValue ofIdentifierName . - If the
source text matched by thisSuperProperty isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
MakeSuperPropertyReference (actualThis,propertyKey,strict).
- LetnewTarget be
GetNewTarget (). Assert :newTargetis an Object .- Letfunc be
GetSuperConstructor (). - LetargList be ?
ArgumentListEvaluation ofArguments . - If
IsConstructor (func) isfalse , throw aTypeError exception. - Letresult be ?
Construct (func,argList,newTarget). - LetthisER be
GetThisEnvironment (). - Perform ? thisER.BindThisValue(result).
- LetF bethisER.[[FunctionObject]].
Assert :F is an ECMAScriptfunction object .- Perform ?
InitializeInstanceElements (result,F). - Returnresult.
13.3.7.2 GetSuperConstructor ( )
The abstract operation GetSuperConstructor takes no arguments and returns an
- LetenvRec be
GetThisEnvironment (). Assert :envRec is aFunction Environment Record .- LetactiveFunction beenvRec.[[FunctionObject]].
Assert :activeFunction is an ECMAScriptfunction object .- LetsuperConstructor be ! activeFunction.[[GetPrototypeOf]]().
- ReturnsuperConstructor.
13.3.7.3 MakeSuperPropertyReference (actualThis,propertyKey,strict )
The abstract operation MakeSuperPropertyReference takes argumentsactualThis (an
- Letenv be
GetThisEnvironment (). Assert :env.HasSuperBinding() istrue .- LetbaseValue be ? env.GetSuperBase().
- Return the
Reference Record {[[Base]]:baseValue,[[ReferencedName]]:propertyKey,[[Strict]]:strict,[[ThisValue]]:actualThis }.
13.3.8 Argument Lists
The evaluation of an argument list produces a
13.3.8.1 Runtime Semantics: ArgumentListEvaluation
The
- Return a new empty
List .
- Letref be ?
Evaluation ofAssignmentExpression . - Letarg be ?
GetValue (ref). - Return «arg ».
- Letlist be a new empty
List . - LetspreadRef be ?
Evaluation ofAssignmentExpression . - LetspreadObj be ?
GetValue (spreadRef). - LetiteratorRecord be ?
GetIterator (spreadObj,sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returnlist. - Appendnext tolist.
- Letnext be ?
- LetprecedingArgs be ?
ArgumentListEvaluation ofArgumentList . - Letref be ?
Evaluation ofAssignmentExpression . - Letarg be ?
GetValue (ref). - Return the
list-concatenation ofprecedingArgs and «arg ».
- LetprecedingArgs be ?
ArgumentListEvaluation ofArgumentList . - LetspreadRef be ?
Evaluation ofAssignmentExpression . - LetiteratorRecord be ?
GetIterator (?GetValue (spreadRef),sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returnprecedingArgs. - Appendnext toprecedingArgs.
- Letnext be ?
- LettemplateLiteral be this
TemplateLiteral . - LetsiteObj be
GetTemplateObject (templateLiteral). - Return «siteObj ».
- LettemplateLiteral be this
TemplateLiteral . - LetsiteObj be
GetTemplateObject (templateLiteral). - Letremaining be ?
ArgumentListEvaluation ofSubstitutionTemplate . - Return the
list-concatenation of «siteObj » andremaining.
- LetfirstSubRef be ?
Evaluation ofExpression . - LetfirstSub be ?
GetValue (firstSubRef). - LetrestSub be ?
SubstitutionEvaluation ofTemplateSpans . Assert :restSub is a possibly emptyList .- Return the
list-concatenation of «firstSub » andrestSub.
13.3.9 Optional Chains
?..13.3.9.1 Runtime Semantics: Evaluation
- LetbaseReference be ?
Evaluation ofMemberExpression . - LetbaseValue be ?
GetValue (baseReference). - IfbaseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with argumentsbaseValue andbaseReference.
- LetbaseReference be ?
Evaluation ofCallExpression . - LetbaseValue be ?
GetValue (baseReference). - IfbaseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with argumentsbaseValue andbaseReference.
- LetbaseReference be ?
Evaluation ofOptionalExpression . - LetbaseValue be ?
GetValue (baseReference). - IfbaseValue is either
undefined ornull , then- Return
undefined .
- Return
- Return ?
ChainEvaluation ofOptionalChain with argumentsbaseValue andbaseReference.
13.3.9.2 Runtime Semantics: ChainEvaluation
The
- LetthisChain be this
OptionalChain . - LettailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (baseValue,baseReference,Arguments ,tailCall).
- If the
source text matched by thisOptionalChain isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
EvaluatePropertyAccessWithExpressionKey (baseValue,Expression ,strict).
- If the
source text matched by thisOptionalChain isstrict mode code , letstrict betrue ; else letstrict befalse . - Return
EvaluatePropertyAccessWithIdentifierKey (baseValue,IdentifierName ,strict).
- LetfieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (baseValue,fieldNameString).
- LetoptionalChain be
OptionalChain . - LetnewReference be ?
ChainEvaluation ofoptionalChain with argumentsbaseValue andbaseReference. - LetnewValue be ?
GetValue (newReference). - LetthisChain be this
OptionalChain . - LettailCall be
IsInTailPosition (thisChain). - Return ?
EvaluateCall (newValue,newReference,Arguments ,tailCall).
- LetoptionalChain be
OptionalChain . - LetnewReference be ?
ChainEvaluation ofoptionalChain with argumentsbaseValue andbaseReference. - LetnewValue be ?
GetValue (newReference). - If the
source text matched by thisOptionalChain isstrict mode code , letstrict betrue ; else letstrict befalse . - Return ?
EvaluatePropertyAccessWithExpressionKey (newValue,Expression ,strict).
- LetoptionalChain be
OptionalChain . - LetnewReference be ?
ChainEvaluation ofoptionalChain with argumentsbaseValue andbaseReference. - LetnewValue be ?
GetValue (newReference). - If the
source text matched by thisOptionalChain isstrict mode code , letstrict betrue ; else letstrict befalse . - Return
EvaluatePropertyAccessWithIdentifierKey (newValue,IdentifierName ,strict).
- LetoptionalChain be
OptionalChain . - LetnewReference be ?
ChainEvaluation ofoptionalChain with argumentsbaseValue andbaseReference. - LetnewValue be ?
GetValue (newReference). - LetfieldNameString be the
StringValue ofPrivateIdentifier . - Return
MakePrivateReference (newValue,fieldNameString).
13.3.10 Import Calls
13.3.10.1 Runtime Semantics: Evaluation
- Letreferrer be
GetActiveScriptOrModule (). - Ifreferrer is
null , setreferrer tothe current Realm Record . - LetargRef be ?
Evaluation ofAssignmentExpression . - Letspecifier be ?
GetValue (argRef). - LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetspecifierString be
Completion (ToString (specifier)). IfAbruptRejectPromise (specifierString,promiseCapability).- Perform
HostLoadImportedModule (referrer,specifierString,empty ,promiseCapability). - ReturnpromiseCapability.[[Promise]].
13.3.10.1.1 ContinueDynamicImport (promiseCapability,moduleCompletion )
The abstract operation ContinueDynamicImport takes argumentspromiseCapability (aimport()
- IfmoduleCompletion is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «moduleCompletion.[[Value]] »). - Return
unused .
- Perform !
- Letmodule bemoduleCompletion.[[Value]].
- LetloadPromise bemodule.LoadRequestedModules().
- LetrejectedClosure be a new
Abstract Closure with parameters (reason) that capturespromiseCapability and performs the following steps when called:- Perform !
Call (promiseCapability.[[Reject]],undefined , «reason »). - Return
unused .
- Perform !
- LetonRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - LetlinkAndEvaluateClosure be a new
Abstract Closure with no parameters that capturesmodule,promiseCapability, andonRejected and performs the following steps when called:- Letlink be
Completion (module.Link()). - Iflink is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «link.[[Value]] »). - Return
unused .
- Perform !
- LetevaluatePromise bemodule.Evaluate().
- LetfulfilledClosure be a new
Abstract Closure with no parameters that capturesmodule andpromiseCapability and performs the following steps when called:- Letnamespace be
GetModuleNamespace (module). - Perform !
Call (promiseCapability.[[Resolve]],undefined , «namespace »). - Return
unused .
- Letnamespace be
- LetonFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - Perform
PerformPromiseThen (evaluatePromise,onFulfilled,onRejected). - Return
unused .
- Letlink be
- LetlinkAndEvaluate be
CreateBuiltinFunction (linkAndEvaluateClosure, 0,"" , « »). - Perform
PerformPromiseThen (loadPromise,linkAndEvaluate,onRejected). - Return
unused .
13.3.11 Tagged Templates
A tagged template is a function call where the arguments of the call are derived from a
13.3.11.1 Runtime Semantics: Evaluation
- LettagRef be ?
Evaluation ofMemberExpression . - LettagFunc be ?
GetValue (tagRef). - LetthisCall be this
MemberExpression . - LettailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc,tagRef,TemplateLiteral ,tailCall).
- LettagRef be ?
Evaluation ofCallExpression . - LettagFunc be ?
GetValue (tagRef). - LetthisCall be this
CallExpression . - LettailCall be
IsInTailPosition (thisCall). - Return ?
EvaluateCall (tagFunc,tagRef,TemplateLiteral ,tailCall).
13.3.12 Meta Properties
13.3.12.1 Runtime Semantics: Evaluation
- Return
GetNewTarget ().
- Letmodule be
GetActiveScriptOrModule (). Assert :module is aSource Text Module Record .- LetimportMeta bemodule.[[ImportMeta]].
- IfimportMeta is
empty , then- SetimportMeta to
OrdinaryObjectCreate (null ). - LetimportMetaValues be
HostGetImportMetaProperties (module). - For each
Record {[[Key]],[[Value]] }p ofimportMetaValues, do- Perform !
CreateDataPropertyOrThrow (importMeta,p.[[Key]],p.[[Value]]).
- Perform !
- Perform
HostFinalizeImportMeta (importMeta,module). - Setmodule.[[ImportMeta]] toimportMeta.
- ReturnimportMeta.
- SetimportMeta to
- Else,
Assert :importMetais an Object .- ReturnimportMeta.
13.3.12.1.1 HostGetImportMetaProperties (moduleRecord )
Theimport.meta.
The default implementation of HostGetImportMetaProperties is to return a new empty
13.3.12.1.2 HostFinalizeImportMeta (importMeta,moduleRecord )
Theimport.meta.
Most
The default implementation of HostFinalizeImportMeta is to return
13.4 Update Expressions
Syntax
13.4.1 Static Semantics: Early Errors
- It is an early Syntax Error if
AssignmentTargetType ofLeftHandSideExpression is notsimple .
- It is an early Syntax Error if
AssignmentTargetType ofUnaryExpression is notsimple .
13.4.2 Postfix Increment Operator
13.4.2.1 Runtime Semantics: Evaluation
- Letlhs be ?
Evaluation ofLeftHandSideExpression . - LetoldValue be ?
ToNumeric (?GetValue (lhs)). - IfoldValue
is a Number , then- LetnewValue be
Number::add (oldValue,1 𝔽).
- LetnewValue be
- Else,
Assert :oldValueis a BigInt .- LetnewValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (lhs,newValue). - ReturnoldValue.
13.4.3 Postfix Decrement Operator
13.4.3.1 Runtime Semantics: Evaluation
- Letlhs be ?
Evaluation ofLeftHandSideExpression . - LetoldValue be ?
ToNumeric (?GetValue (lhs)). - IfoldValue
is a Number , then- LetnewValue be
Number::subtract (oldValue,1 𝔽).
- LetnewValue be
- Else,
Assert :oldValueis a BigInt .- LetnewValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (lhs,newValue). - ReturnoldValue.
13.4.4 Prefix Increment Operator
13.4.4.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - LetoldValue be ?
ToNumeric (?GetValue (expr)). - IfoldValue
is a Number , then- LetnewValue be
Number::add (oldValue,1 𝔽).
- LetnewValue be
- Else,
Assert :oldValueis a BigInt .- LetnewValue be
BigInt::add (oldValue,1 ℤ).
- Perform ?
PutValue (expr,newValue). - ReturnnewValue.
13.4.5 Prefix Decrement Operator
13.4.5.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - LetoldValue be ?
ToNumeric (?GetValue (expr)). - IfoldValue
is a Number , then- LetnewValue be
Number::subtract (oldValue,1 𝔽).
- LetnewValue be
- Else,
Assert :oldValueis a BigInt .- LetnewValue be
BigInt::subtract (oldValue,1 ℤ).
- Perform ?
PutValue (expr,newValue). - ReturnnewValue.
13.5 Unary Operators
Syntax
13.5.1 Thedelete Operator
13.5.1.1 Static Semantics: Early Errors
- It is a Syntax Error if the
UnaryExpression is contained instrict mode code and the derivedUnaryExpression isPrimaryExpression : IdentifierReference MemberExpression : MemberExpression . PrivateIdentifier CallExpression : CallExpression . PrivateIdentifier OptionalChain : ?. PrivateIdentifier OptionalChain : OptionalChain . PrivateIdentifier It is a Syntax Error if the derived
UnaryExpression isPrimaryExpression : CoverParenthesizedExpressionAndArrowParameterList
andCoverParenthesizedExpressionAndArrowParameterList ultimately derives a phrase that, if used in place ofUnaryExpression , would produce a Syntax Error according to these rules. This rule is recursively applied.
The last rule means that expressions such asdelete (((foo))) produce
13.5.1.2 Runtime Semantics: Evaluation
- Letref be ?
Evaluation ofUnaryExpression . - Ifref is not a
Reference Record , returntrue . - If
IsUnresolvableReference (ref) istrue , thenAssert :ref.[[Strict]] isfalse .- Return
true .
- If
IsPropertyReference (ref) istrue , thenAssert :IsPrivateReference (ref) isfalse .- If
IsSuperReference (ref) istrue , throw aReferenceError exception. - LetbaseObj be ?
ToObject (ref.[[Base]]). - LetdeleteStatus be ? baseObj.[[Delete]](ref.[[ReferencedName]]).
- IfdeleteStatus is
false andref.[[Strict]] istrue , throw aTypeError exception. - ReturndeleteStatus.
- Else,
- Letbase beref.[[Base]].
Assert :base is anEnvironment Record .- Return ? base.DeleteBinding(ref.[[ReferencedName]]).
When adelete operator occurs withindelete operator occurs within
The object that may be created in step
13.5.2 Thevoid Operator
13.5.2.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - Perform ?
GetValue (expr). - Return
undefined .
13.5.3 Thetypeof Operator
13.5.3.1 Runtime Semantics: Evaluation
- Letval be ?
Evaluation ofUnaryExpression . - Ifval is a
Reference Record , then- If
IsUnresolvableReference (val) istrue , return"undefined" .
- If
- Setval to ?
GetValue (val). - Ifval is
undefined , return"undefined" . - Ifval is
null , return"object" . - Ifval
is a String , return"string" . - Ifval
is a Symbol , return"symbol" . - Ifval
is a Boolean , return"boolean" . - Ifval
is a Number , return"number" . - Ifval
is a BigInt , return"bigint" . Assert :valis an Object .- NOTE: This step is replaced in section
B.3.6.3 . - Ifval has a[[Call]] internal slot, return
"function" . - Return
"object" .
13.5.4 Unary+ Operator
The unary + operator converts its operand to
13.5.4.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - Return ?
ToNumber (?GetValue (expr)).
13.5.5 Unary- Operator
The unary- operator converts its operand to a numeric value and then negates it. Negating
13.5.5.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - LetoldValue be ?
ToNumeric (?GetValue (expr)). - IfoldValue
is a Number , then- Return
Number::unaryMinus (oldValue).
- Return
- Else,
Assert :oldValueis a BigInt .- Return
BigInt::unaryMinus (oldValue).
13.5.6 Bitwise NOT Operator (~ )
13.5.6.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - LetoldValue be ?
ToNumeric (?GetValue (expr)). - IfoldValue
is a Number , then- Return
Number::bitwiseNOT (oldValue).
- Return
- Else,
Assert :oldValueis a BigInt .- Return
BigInt::bitwiseNOT (oldValue).
13.5.7 Logical NOT Operator (! )
13.5.7.1 Runtime Semantics: Evaluation
- Letexpr be ?
Evaluation ofUnaryExpression . - LetoldValue be
ToBoolean (?GetValue (expr)). - IfoldValue is
true , returnfalse . - Return
true .
13.6 Exponentiation Operator
Syntax
13.6.1 Runtime Semantics: Evaluation
13.7 Multiplicative Operators
Syntax
- The
*operator performs multiplication, producing the product of its operands. - The
/operator performs division, producing the quotient of its operands. - The
%operator yields the remainder of its operands from an implied division.
13.7.1 Runtime Semantics: Evaluation
- LetopText be the
source text matched by MultiplicativeOperator . - Return ?
EvaluateStringOrNumericBinaryExpression (MultiplicativeExpression ,opText,ExponentiationExpression ).
13.8 Additive Operators
Syntax
13.8.1 The Addition Operator (+ )
The addition operator either performs string concatenation or numeric addition.
13.8.1.1 Runtime Semantics: Evaluation
13.8.2 The Subtraction Operator (- )
The- operator performs subtraction, producing the difference of its operands.
13.8.2.1 Runtime Semantics: Evaluation
13.9 Bitwise Shift Operators
Syntax
13.9.1 The Left Shift Operator (<< )
Performs a bitwise left shift operation on the left operand by the amount specified by the right operand.
13.9.1.1 Runtime Semantics: Evaluation
13.9.2 The Signed Right Shift Operator (>> )
Performs a sign-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.2.1 Runtime Semantics: Evaluation
13.9.3 The Unsigned Right Shift Operator (>>> )
Performs a zero-filling bitwise right shift operation on the left operand by the amount specified by the right operand.
13.9.3.1 Runtime Semantics: Evaluation
13.10 Relational Operators
The result of evaluating a relational operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
The[In] grammar parameter is needed to avoid confusing thein operator in a relational expression with thein operator in afor statement.
13.10.1 Runtime Semantics: Evaluation
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Letr be ?
IsLessThan (lval,rval,true ). - Ifr is
undefined , returnfalse . Otherwise, returnr.
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Letr be ?
IsLessThan (rval,lval,false ). - Ifr is
undefined , returnfalse . Otherwise, returnr.
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Letr be ?
IsLessThan (rval,lval,false ). - Ifr is either
true orundefined , returnfalse . Otherwise, returntrue .
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Letr be ?
IsLessThan (lval,rval,true ). - Ifr is either
true orundefined , returnfalse . Otherwise, returntrue .
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Return ?
InstanceofOperator (lval,rval).
- Letlref be ?
Evaluation ofRelationalExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Ifrval
is not an Object , throw aTypeError exception. - Return ?
HasProperty (rval, ?ToPropertyKey (lval)).
- LetprivateIdentifier be the
StringValue ofPrivateIdentifier . - Letrref be ?
Evaluation ofShiftExpression . - Letrval be ?
GetValue (rref). - Ifrval
is not an Object , throw aTypeError exception. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetprivateName be
ResolvePrivateIdentifier (privateEnv,privateIdentifier). - If
PrivateElementFind (rval,privateName) is notempty , returntrue . - Return
false .
13.10.2 InstanceofOperator (V,target )
The abstract operation InstanceofOperator takes argumentsV (an
- Iftarget
is not an Object , throw aTypeError exception. - LetinstOfHandler be ?
GetMethod (target,@@hasInstance ). - IfinstOfHandler is not
undefined , then - If
IsCallable (target) isfalse , throw aTypeError exception. - Return ?
OrdinaryHasInstance (target,V).
Stepsinstanceof operator semantics. If an object does not define or inheritinstanceof semantics.
13.11 Equality Operators
The result of evaluating an equality operator is always of type Boolean, reflecting whether the relationship named by the operator holds between its two operands.
Syntax
13.11.1 Runtime Semantics: Evaluation
- Letlref be ?
Evaluation ofEqualityExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofRelationalExpression . - Letrval be ?
GetValue (rref). - Return ?
IsLooselyEqual (rval,lval).
- Letlref be ?
Evaluation ofEqualityExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofRelationalExpression . - Letrval be ?
GetValue (rref). - Letr be ?
IsLooselyEqual (rval,lval). - Ifr is
true , returnfalse . Otherwise, returntrue .
- Letlref be ?
Evaluation ofEqualityExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofRelationalExpression . - Letrval be ?
GetValue (rref). - Return
IsStrictlyEqual (rval,lval).
- Letlref be ?
Evaluation ofEqualityExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofRelationalExpression . - Letrval be ?
GetValue (rref). - Letr be
IsStrictlyEqual (rval,lval). - Ifr is
true , returnfalse . Otherwise, returntrue .
Given the above definition of equality:
- String comparison can be forced by:
`${a}` == `${b}`. - Numeric comparison can be forced by:
+a == +b. - Boolean comparison can be forced by:
!a == !b.
The equality operators maintain the following invariants:
A != Bis equivalent to!(A == B).A == Bis equivalent toB == A, except in the order of evaluation ofAandB.
The equality operator is not always transitive. For example, there might be two distinct String objects, each representing the same String value; each String object would be considered equal to the String value by the== operator, but the two String objects would not be equal to each other. For example:
new String("a") == "a"and"a" == new String("a")are bothtrue .new String("a") == new String("a")isfalse .
Comparison of Strings uses a simple equality test on sequences of code unit values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore Strings values that are canonically equal according to the Unicode Standard could test as unequal. In effect this algorithm assumes that both Strings are already in normalized form.
13.12 Binary Bitwise Operators
Syntax
13.12.1 Runtime Semantics: Evaluation
13.13 Binary Logical Operators
Syntax
The value produced by a&& or|| operator is not necessarily of type Boolean. The value produced will always be the value of one of the two operand expressions.
13.13.1 Runtime Semantics: Evaluation
- Letlref be ?
Evaluation ofLogicalANDExpression . - Letlval be ?
GetValue (lref). - Letlbool be
ToBoolean (lval). - Iflbool is
false , returnlval. - Letrref be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rref).
- Letlref be ?
Evaluation ofLogicalORExpression . - Letlval be ?
GetValue (lref). - Letlbool be
ToBoolean (lval). - Iflbool is
true , returnlval. - Letrref be ?
Evaluation ofLogicalANDExpression . - Return ?
GetValue (rref).
- Letlref be ?
Evaluation ofCoalesceExpressionHead . - Letlval be ?
GetValue (lref). - Iflval is either
undefined ornull , then- Letrref be ?
Evaluation ofBitwiseORExpression . - Return ?
GetValue (rref).
- Letrref be ?
- Else,
- Returnlval.
13.14 Conditional Operator (? : )
Syntax
The grammar for a
13.14.1 Runtime Semantics: Evaluation
- Letlref be ?
Evaluation ofShortCircuitExpression . - Letlval be
ToBoolean (?GetValue (lref)). - Iflval is
true , then- LettrueRef be ?
Evaluation of the firstAssignmentExpression . - Return ?
GetValue (trueRef).
- LettrueRef be ?
- Else,
- LetfalseRef be ?
Evaluation of the secondAssignmentExpression . - Return ?
GetValue (falseRef).
- LetfalseRef be ?
13.15 Assignment Operators
Syntax
13.15.1 Static Semantics: Early Errors
If
If
- It is a Syntax Error if
AssignmentTargetType ofLeftHandSideExpression is notsimple .
- It is a Syntax Error if
AssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.2 Runtime Semantics: Evaluation
- If
LeftHandSideExpression is neither anObjectLiteral nor anArrayLiteral , then- Letlref be ?
Evaluation ofLeftHandSideExpression . - If
IsAnonymousFunctionDefinition (AssignmentExpression ) andIsIdentifierRef ofLeftHandSideExpression are bothtrue , then- Letrval be ?
NamedEvaluation ofAssignmentExpression with argumentlref.[[ReferencedName]].
- Letrval be ?
- Else,
- Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref).
- Letrref be ?
- Perform ?
PutValue (lref,rval). - Returnrval.
- Letlref be ?
- LetassignmentPattern be the
AssignmentPattern that iscovered byLeftHandSideExpression . - Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref). - Perform ?
DestructuringAssignmentEvaluation ofassignmentPattern with argumentrval. - Returnrval.
- Letlref be ?
Evaluation ofLeftHandSideExpression . - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref). - LetassignmentOpText be the
source text matched by AssignmentOperator . - LetopText be the sequence of Unicode code points associated withassignmentOpText in the following table:
assignmentOpText opText **=***=*/=/%=%+=+-=-<<=<<>>=>>>>>=>>>&=&^=^|=| - Letr be ?
ApplyStringOrNumericBinaryOperator (lval,opText,rval). - Perform ?
PutValue (lref,r). - Returnr.
- Letlref be ?
Evaluation ofLeftHandSideExpression . - Letlval be ?
GetValue (lref). - Letlbool be
ToBoolean (lval). - Iflbool is
false , returnlval. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Letrval be ?
NamedEvaluation ofAssignmentExpression with argumentlref.[[ReferencedName]].
- Letrval be ?
- Else,
- Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref).
- Letrref be ?
- Perform ?
PutValue (lref,rval). - Returnrval.
- Letlref be ?
Evaluation ofLeftHandSideExpression . - Letlval be ?
GetValue (lref). - Letlbool be
ToBoolean (lval). - Iflbool is
true , returnlval. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Letrval be ?
NamedEvaluation ofAssignmentExpression with argumentlref.[[ReferencedName]].
- Letrval be ?
- Else,
- Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref).
- Letrref be ?
- Perform ?
PutValue (lref,rval). - Returnrval.
- Letlref be ?
Evaluation ofLeftHandSideExpression . - Letlval be ?
GetValue (lref). - Iflval is neither
undefined nornull , returnlval. - If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue andIsIdentifierRef ofLeftHandSideExpression istrue , then- Letrval be ?
NamedEvaluation ofAssignmentExpression with argumentlref.[[ReferencedName]].
- Letrval be ?
- Else,
- Letrref be ?
Evaluation ofAssignmentExpression . - Letrval be ?
GetValue (rref).
- Letrref be ?
- Perform ?
PutValue (lref,rval). - Returnrval.
When this expression occurs within
13.15.3 ApplyStringOrNumericBinaryOperator (lval,opText,rval )
The abstract operation ApplyStringOrNumericBinaryOperator takes argumentslval (an**,*,/,%,+,-,<<,>>,>>>,&,^, or|), andrval (an
- IfopText is
+, then- Letlprim be ?
ToPrimitive (lval). - Letrprim be ?
ToPrimitive (rval). - Iflprim
is a String orrprimis a String , then- Letlstr be ?
ToString (lprim). - Letrstr be ?
ToString (rprim). - Return the
string-concatenation oflstr andrstr.
- Letlstr be ?
- Setlval tolprim.
- Setrval torprim.
- Letlprim be ?
- NOTE: At this point, it must be a numeric operation.
- Letlnum be ?
ToNumeric (lval). - Letrnum be ?
ToNumeric (rval). - If
Type (lnum) is notType (rnum), throw aTypeError exception. - Iflnum
is a BigInt , then- IfopText is
**, return ?BigInt::exponentiate (lnum,rnum). - IfopText is
/, return ?BigInt::divide (lnum,rnum). - IfopText is
%, return ?BigInt::remainder (lnum,rnum). - IfopText is
>>>, return ?BigInt::unsignedRightShift (lnum,rnum).
- IfopText is
- Letoperation be the abstract operation associated withopText and
Type (lnum) in the following table:opText Type (lnum)operation **Number Number::exponentiate *Number Number::multiply *BigInt BigInt::multiply /Number Number::divide %Number Number::remainder +Number Number::add +BigInt BigInt::add -Number Number::subtract -BigInt BigInt::subtract <<Number Number::leftShift <<BigInt BigInt::leftShift >>Number Number::signedRightShift >>BigInt BigInt::signedRightShift >>>Number Number::unsignedRightShift &Number Number::bitwiseAND &BigInt BigInt::bitwiseAND ^Number Number::bitwiseXOR ^BigInt BigInt::bitwiseXOR |Number Number::bitwiseOR |BigInt BigInt::bitwiseOR - Returnoperation(lnum,rnum).
No hint is provided in the calls to
Step
13.15.4 EvaluateStringOrNumericBinaryExpression (leftOperand,opText,rightOperand )
The abstract operation EvaluateStringOrNumericBinaryExpression takes argumentsleftOperand (a
- Letlref be ?
Evaluation ofleftOperand. - Letlval be ?
GetValue (lref). - Letrref be ?
Evaluation ofrightOperand. - Letrval be ?
GetValue (rref). - Return ?
ApplyStringOrNumericBinaryOperator (lval,opText,rval).
13.15.5 Destructuring Assignment
Supplemental Syntax
In certain circumstances when processing an instance of the production
the interpretation of
13.15.5.1 Static Semantics: Early Errors
- It is a Syntax Error if
AssignmentTargetType ofIdentifierReference is notsimple .
- It is a Syntax Error if
DestructuringAssignmentTarget is either anArrayLiteral or anObjectLiteral .
If
If
- It is a Syntax Error if
AssignmentTargetType ofLeftHandSideExpression is notsimple .
13.15.5.2 Runtime Semantics: DestructuringAssignmentEvaluation
The
- Perform ?
RequireObjectCoercible (value). - Return
unused .
- Perform ?
RequireObjectCoercible (value). - Perform ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argumentvalue. - Return
unused .
- Perform ?
RequireObjectCoercible (value). - LetexcludedNames be a new empty
List . - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with argumentsvalue andexcludedNames.
- Perform ?
RequireObjectCoercible (value). - LetexcludedNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argumentvalue. - Return ?
RestDestructuringAssignmentEvaluation ofAssignmentRestProperty with argumentsvalue andexcludedNames.
- LetiteratorRecord be ?
GetIterator (value,sync ). - Return ?
IteratorClose (iteratorRecord,NormalCompletion (unused )).
- LetiteratorRecord be ?
GetIterator (value,sync ). - Letresult be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord). - IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,result). - Returnresult.
- LetiteratorRecord be ?
GetIterator (value,sync ). - If
Elision is present, then- Letstatus be
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord). - Ifstatus is an
abrupt completion , thenAssert :iteratorRecord.[[Done]] istrue .- Return ? status.
- Letstatus be
- Letresult be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argumentiteratorRecord). - IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,result). - Returnresult.
- LetiteratorRecord be ?
GetIterator (value,sync ). - Letresult be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argumentiteratorRecord). - IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,result). - Returnresult.
- LetiteratorRecord be ?
GetIterator (value,sync ). - Letstatus be
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argumentiteratorRecord). - Ifstatus is an
abrupt completion , then- IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,status). - Return ? status.
- IfiteratorRecord.[[Done]] is
- If
Elision is present, then- Setstatus to
Completion (IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord). - Ifstatus is an
abrupt completion , thenAssert :iteratorRecord.[[Done]] istrue .- Return ? status.
- Setstatus to
- If
AssignmentRestElement is present, then- Setstatus to
Completion (IteratorDestructuringAssignmentEvaluation ofAssignmentRestElement with argumentiteratorRecord).
- Setstatus to
- IfiteratorRecord.[[Done]] is
false , return ?IteratorClose (iteratorRecord,status). - Return ? status.
13.15.5.3 Runtime Semantics: PropertyDestructuringAssignmentEvaluation
The
- LetpropertyNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentPropertyList with argumentvalue. - LetnextNames be ?
PropertyDestructuringAssignmentEvaluation ofAssignmentProperty with argumentvalue. - Return the
list-concatenation ofpropertyNames andnextNames.
- LetP be
StringValue ofIdentifierReference . - Letlref be ?
ResolveBinding (P). - Letv be ?
GetV (value,P). - If
Initializer is present andv isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Setv to ?
NamedEvaluation ofInitializer with argumentP.
- Setv to ?
- Else,
- LetdefaultValue be ?
Evaluation ofInitializer . - Setv to ?
GetValue (defaultValue).
- LetdefaultValue be ?
- If
- Perform ?
PutValue (lref,v). - Return «P ».
- Letname be ?
Evaluation ofPropertyName . - Perform ?
KeyedDestructuringAssignmentEvaluation ofAssignmentElement with argumentsvalue andname. - Return «name ».
13.15.5.4 Runtime Semantics: RestDestructuringAssignmentEvaluation
The
- Letlref be ?
Evaluation ofDestructuringAssignmentTarget . - LetrestObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj,value,excludedNames). - Return ?
PutValue (lref,restObj).
13.15.5.5 Runtime Semantics: IteratorDestructuringAssignmentEvaluation
The
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argumentiteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElementList with argumentiteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElisionElement with argumentiteratorRecord.
- Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argumentiteratorRecord.
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord. - Return ?
IteratorDestructuringAssignmentEvaluation ofAssignmentElement with argumentiteratorRecord.
- IfiteratorRecord.[[Done]] is
false , then- Letnext be
Completion (IteratorStep (iteratorRecord)). - Ifnext is an
abrupt completion , setiteratorRecord.[[Done]] totrue . ReturnIfAbrupt (next).- Ifnext is
false , setiteratorRecord.[[Done]] totrue .
- Letnext be
- Return
unused .
- Perform ?
IteratorDestructuringAssignmentEvaluation ofElision with argumentiteratorRecord. - IfiteratorRecord.[[Done]] is
false , then- Letnext be
Completion (IteratorStep (iteratorRecord)). - Ifnext is an
abrupt completion , setiteratorRecord.[[Done]] totrue . ReturnIfAbrupt (next).- Ifnext is
false , setiteratorRecord.[[Done]] totrue .
- Letnext be
- Return
unused .
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Letlref be ?
Evaluation ofDestructuringAssignmentTarget .
- Letlref be ?
- Letvalue be
undefined . - IfiteratorRecord.[[Done]] is
false , then- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Setvalue tonext.
- Letnext be ?
- If
Initializer is present andvalue isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue andIsIdentifierRef ofDestructuringAssignmentTarget istrue , then- Letv be ?
NamedEvaluation ofInitializer with argumentlref.[[ReferencedName]].
- Letv be ?
- Else,
- LetdefaultValue be ?
Evaluation ofInitializer . - Letv be ?
GetValue (defaultValue).
- LetdefaultValue be ?
- If
- Else,
- Letv bevalue.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- LetnestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation ofnestedAssignmentPattern with argumentv.
- LetnestedAssignmentPattern be the
- Return ?
PutValue (lref,v).
Left to right evaluation order is maintained by evaluating a
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Letlref be ?
Evaluation ofDestructuringAssignmentTarget .
- Letlref be ?
- LetA be !
ArrayCreate (0). - Letn be 0.
- Repeat, whileiteratorRecord.[[Done]] is
false ,- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is not
done , then- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),next). - Setn ton + 1.
- Perform !
- Letnext be ?
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Return ?
PutValue (lref,A).
- Return ?
- LetnestedAssignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation ofnestedAssignmentPattern with argumentA.
13.15.5.6 Runtime Semantics: KeyedDestructuringAssignmentEvaluation
The
- If
DestructuringAssignmentTarget is neither anObjectLiteral nor anArrayLiteral , then- Letlref be ?
Evaluation ofDestructuringAssignmentTarget .
- Letlref be ?
- Letv be ?
GetV (value,propertyName). - If
Initializer is present andv isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) andIsIdentifierRef ofDestructuringAssignmentTarget are bothtrue , then- LetrhsValue be ?
NamedEvaluation ofInitializer with argumentlref.[[ReferencedName]].
- LetrhsValue be ?
- Else,
- LetdefaultValue be ?
Evaluation ofInitializer . - LetrhsValue be ?
GetValue (defaultValue).
- LetdefaultValue be ?
- If
- Else,
- LetrhsValue bev.
- If
DestructuringAssignmentTarget is either anObjectLiteral or anArrayLiteral , then- LetassignmentPattern be the
AssignmentPattern that iscovered byDestructuringAssignmentTarget . - Return ?
DestructuringAssignmentEvaluation ofassignmentPattern with argumentrhsValue.
- LetassignmentPattern be the
- Return ?
PutValue (lref,rhsValue).
13.16 Comma Operator (, )
Syntax
13.16.1 Runtime Semantics: Evaluation
- Letlref be ?
Evaluation ofExpression . - Perform ?
GetValue (lref). - Letrref be ?
Evaluation ofAssignmentExpression . - Return ?
GetValue (rref).
14 ECMAScript Language: Statements and Declarations
Syntax
14.1 Statement Semantics
14.1.1 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofFunctionDeclaration .
- LetnewLabelSet be a new empty
List . - Return ?
LabelledEvaluation of thisBreakableStatement with argumentnewLabelSet.
14.2 Block
Syntax
14.2.1 Static Semantics: Early Errors
- It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
14.2.2 Runtime Semantics: Evaluation
- Return
empty .
- LetoldEnv be the
running execution context 's LexicalEnvironment. - LetblockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (StatementList ,blockEnv). - Set the
running execution context 's LexicalEnvironment toblockEnv. - LetblockValue be
Completion (Evaluation ofStatementList ). - Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ? blockValue.
No matter how control leaves the
- Letsl be ?
Evaluation ofStatementList . - Lets be
Completion (Evaluation ofStatementListItem ). - Return ?
UpdateEmpty (s,sl).
The value of aeval function all return the value 1:
eval("1;;;;;")eval("1;{}")eval("1;var a;")14.2.3 BlockDeclarationInstantiation (code,env )
The abstract operation BlockDeclarationInstantiation takes argumentscode (a
When a
It performs the following steps when called:
- Letdeclarations be the
LexicallyScopedDeclarations ofcode. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - For each elementd ofdeclarations, do
- For each elementdn of the
BoundNames ofd, do- If
IsConstantDeclaration ofd istrue , then- Perform ! env.CreateImmutableBinding(dn,
true ).
- Perform ! env.CreateImmutableBinding(dn,
- Else,
- Perform ! env.CreateMutableBinding(dn,
false ). NOTE: This step is replaced in sectionB.3.2.6 .
- Perform ! env.CreateMutableBinding(dn,
- If
- Ifd is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Letfn be the sole element of the
BoundNames ofd. - Letfo be
InstantiateFunctionObject ofd with argumentsenv andprivateEnv. - Perform ! env.InitializeBinding(fn,fo). NOTE: This step is replaced in section
B.3.2.6 .
- Letfn be the sole element of the
- For each elementdn of the
- Return
unused .
14.3 Declarations and the Variable Statement
14.3.1 Let and Const Declarations
let andconst declarations define variables that are scoped to thelet declaration does not have an
Syntax
14.3.1.1 Static Semantics: Early Errors
- It is a Syntax Error if the
BoundNames ofBindingList contains"let" . - It is a Syntax Error if the
BoundNames ofBindingList contains any duplicate entries.
- It is a Syntax Error if
Initializer is not present andIsConstantDeclaration of theLexicalDeclaration containing thisLexicalBinding istrue .
14.3.1.2 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofBindingList . - Return
empty .
- Perform ?
Evaluation ofBindingList . - Return ?
Evaluation ofLexicalBinding .
- Letlhs be !
ResolveBinding (StringValue ofBindingIdentifier ). - Perform !
InitializeReferencedBinding (lhs,undefined ). - Return
empty .
Aconst declaration.
- LetbindingId be
StringValue ofBindingIdentifier . - Letlhs be !
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Letvalue be ?
NamedEvaluation ofInitializer with argumentbindingId.
- Letvalue be ?
- Else,
- Letrhs be ?
Evaluation ofInitializer . - Letvalue be ?
GetValue (rhs).
- Letrhs be ?
- Perform !
InitializeReferencedBinding (lhs,value). - Return
empty .
- Letrhs be ?
Evaluation ofInitializer . - Letvalue be ?
GetValue (rhs). - Letenv be the
running execution context 's LexicalEnvironment. - Return ?
BindingInitialization ofBindingPattern with argumentsvalue andenv.
14.3.2 Variable Statement
Avar statement declares variables that are scoped to the
Syntax
14.3.2.1 Runtime Semantics: Evaluation
- Perform ?
Evaluation ofVariableDeclarationList . - Return
empty .
- Perform ?
Evaluation ofVariableDeclarationList . - Return ?
Evaluation ofVariableDeclaration .
- Return
empty .
- LetbindingId be
StringValue ofBindingIdentifier . - Letlhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Letvalue be ?
NamedEvaluation ofInitializer with argumentbindingId.
- Letvalue be ?
- Else,
- Letrhs be ?
Evaluation ofInitializer . - Letvalue be ?
GetValue (rhs).
- Letrhs be ?
- Perform ?
PutValue (lhs,value). - Return
empty .
If a
- Letrhs be ?
Evaluation ofInitializer . - Letrval be ?
GetValue (rhs). - Return ?
BindingInitialization ofBindingPattern with argumentsrval andundefined .
14.3.3 Destructuring Binding Patterns
Syntax
14.3.3.1 Runtime Semantics: PropertyBindingInitialization
The
- LetboundNames be ?
PropertyBindingInitialization ofBindingPropertyList with argumentsvalue andenvironment. - LetnextNames be ?
PropertyBindingInitialization ofBindingProperty with argumentsvalue andenvironment. - Return the
list-concatenation ofboundNames andnextNames.
- Letname be the sole element of the
BoundNames ofSingleNameBinding . - Perform ?
KeyedBindingInitialization ofSingleNameBinding with argumentsvalue,environment, andname. - Return «name ».
- LetP be ?
Evaluation ofPropertyName . - Perform ?
KeyedBindingInitialization ofBindingElement with argumentsvalue,environment, andP. - Return «P ».
14.3.3.2 Runtime Semantics: RestBindingInitialization
The
- Letlhs be ?
ResolveBinding (StringValue ofBindingIdentifier ,environment). - LetrestObj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform ?
CopyDataProperties (restObj,value,excludedNames). - Ifenvironment is
undefined , return ?PutValue (lhs,restObj). - Return ?
InitializeReferencedBinding (lhs,restObj).
14.3.3.3 Runtime Semantics: KeyedBindingInitialization
The
When
It is defined piecewise over the following productions:
- Letv be ?
GetV (value,propertyName). - If
Initializer is present andv isundefined , then- LetdefaultValue be ?
Evaluation ofInitializer . - Setv to ?
GetValue (defaultValue).
- LetdefaultValue be ?
- Return ?
BindingInitialization ofBindingPattern with argumentsv andenvironment.
- LetbindingId be
StringValue ofBindingIdentifier . - Letlhs be ?
ResolveBinding (bindingId,environment). - Letv be ?
GetV (value,propertyName). - If
Initializer is present andv isundefined , then- If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Setv to ?
NamedEvaluation ofInitializer with argumentbindingId.
- Setv to ?
- Else,
- LetdefaultValue be ?
Evaluation ofInitializer . - Setv to ?
GetValue (defaultValue).
- LetdefaultValue be ?
- If
- Ifenvironment is
undefined , return ?PutValue (lhs,v). - Return ?
InitializeReferencedBinding (lhs,v).
14.4 Empty Statement
Syntax
14.4.1 Runtime Semantics: Evaluation
- Return
empty .
14.5 Expression Statement
Syntax
Anfunction orclassasync function because that would make it ambiguous with anlet [ because that would make it ambiguous with alet
14.5.1 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofExpression . - Return ?
GetValue (exprRef).
14.6 Theif Statement
Syntax
else] resolves the classic "dangling else" problem in the usual way. That is, when the choice of associatedif is otherwise ambiguous, theelse is associated with the nearest (innermost) of the candidateifs14.6.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsLabelledFunction (the firstStatement ) istrue . - It is a Syntax Error if
IsLabelledFunction (the secondStatement ) istrue .
- It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.6.2 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofExpression . - LetexprValue be
ToBoolean (?GetValue (exprRef)). - IfexprValue is
true , then- LetstmtCompletion be
Completion (Evaluation of the firstStatement ).
- LetstmtCompletion be
- Else,
- LetstmtCompletion be
Completion (Evaluation of the secondStatement ).
- LetstmtCompletion be
- Return ?
UpdateEmpty (stmtCompletion,undefined ).
- LetexprRef be ?
Evaluation ofExpression . - LetexprValue be
ToBoolean (?GetValue (exprRef)). - IfexprValue is
false , then- Return
undefined .
- Return
- Else,
- LetstmtCompletion be
Completion (Evaluation ofStatement ). - Return ?
UpdateEmpty (stmtCompletion,undefined ).
- LetstmtCompletion be
14.7 Iteration Statements
Syntax
14.7.1 Semantics
14.7.1.1 LoopContinues (completion,labelSet )
The abstract operation LoopContinues takes argumentscompletion (a
- Ifcompletion is a
normal completion , returntrue . - Ifcompletion is not a
continue completion , returnfalse . - Ifcompletion.[[Target]] is
empty , returntrue . - IflabelSet containscompletion.[[Target]], return
true . - Return
false .
Within the
14.7.1.2 Runtime Semantics: LoopEvaluation
The
- Return ?
DoWhileLoopEvaluation ofDoWhileStatement with argumentlabelSet.
- Return ?
WhileLoopEvaluation ofWhileStatement with argumentlabelSet.
- Return ?
ForLoopEvaluation ofForStatement with argumentlabelSet.
- Return ?
ForInOfLoopEvaluation ofForInOfStatement with argumentlabelSet.
14.7.2 Thedo-while Statement
Syntax
14.7.2.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.2.2 Runtime Semantics: DoWhileLoopEvaluation
The
- LetV be
undefined . - Repeat,
- LetstmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult,labelSet) isfalse , return ?UpdateEmpty (stmtResult,V). - IfstmtResult.[[Value]] is not
empty , setV tostmtResult.[[Value]]. - LetexprRef be ?
Evaluation ofExpression . - LetexprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , returnV.
- LetstmtResult be
14.7.3 Thewhile Statement
Syntax
14.7.3.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
14.7.3.2 Runtime Semantics: WhileLoopEvaluation
The
- LetV be
undefined . - Repeat,
- LetexprRef be ?
Evaluation ofExpression . - LetexprValue be ?
GetValue (exprRef). - If
ToBoolean (exprValue) isfalse , returnV. - LetstmtResult be
Completion (Evaluation ofStatement ). - If
LoopContinues (stmtResult,labelSet) isfalse , return ?UpdateEmpty (stmtResult,V). - IfstmtResult.[[Value]] is not
empty , setV tostmtResult.[[Value]].
- LetexprRef be ?
14.7.4 Thefor Statement
Syntax
14.7.4.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
- It is a Syntax Error if any element of the
BoundNames ofLexicalDeclaration also occurs in theVarDeclaredNames ofStatement .
14.7.4.2 Runtime Semantics: ForLoopEvaluation
The
- If the first
Expression is present, then- LetexprRef be ?
Evaluation of the firstExpression . - Perform ?
GetValue (exprRef).
- LetexprRef be ?
- If the second
Expression is present, lettest be the secondExpression ; otherwise, lettest beempty . - If the third
Expression is present, letincrement be the thirdExpression ; otherwise, letincrement beempty . - Return ?
ForBodyEvaluation (test,increment,Statement , « »,labelSet).
- Perform ?
Evaluation ofVariableDeclarationList . - If the first
Expression is present, lettest be the firstExpression ; otherwise, lettest beempty . - If the second
Expression is present, letincrement be the secondExpression ; otherwise, letincrement beempty . - Return ?
ForBodyEvaluation (test,increment,Statement , « »,labelSet).
- LetoldEnv be the
running execution context 's LexicalEnvironment. - LetloopEnv be
NewDeclarativeEnvironment (oldEnv). - LetisConst be
IsConstantDeclaration ofLexicalDeclaration . - LetboundNames be the
BoundNames ofLexicalDeclaration . - For each elementdn ofboundNames, do
- IfisConst is
true , then- Perform ! loopEnv.CreateImmutableBinding(dn,
true ).
- Perform ! loopEnv.CreateImmutableBinding(dn,
- Else,
- Perform ! loopEnv.CreateMutableBinding(dn,
false ).
- Perform ! loopEnv.CreateMutableBinding(dn,
- IfisConst is
- Set the
running execution context 's LexicalEnvironment toloopEnv. - LetforDcl be
Completion (Evaluation ofLexicalDeclaration ). - IfforDcl is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ? forDcl.
- Set the
- IfisConst is
false , letperIterationLets beboundNames; otherwise letperIterationLets be a new emptyList . - If the first
Expression is present, lettest be the firstExpression ; otherwise, lettest beempty . - If the second
Expression is present, letincrement be the secondExpression ; otherwise, letincrement beempty . - LetbodyResult be
Completion (ForBodyEvaluation (test,increment,Statement ,perIterationLets,labelSet)). - Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ? bodyResult.
14.7.4.3 ForBodyEvaluation (test,increment,stmt,perIterationBindings,labelSet )
The abstract operation ForBodyEvaluation takes argumentstest (an
- LetV be
undefined . - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - Repeat,
- Iftest is not
empty , then- LettestRef be ?
Evaluation oftest. - LettestValue be ?
GetValue (testRef). - If
ToBoolean (testValue) isfalse , returnV.
- LettestRef be ?
- Letresult be
Completion (Evaluation ofstmt). - If
LoopContinues (result,labelSet) isfalse , return ?UpdateEmpty (result,V). - Ifresult.[[Value]] is not
empty , setV toresult.[[Value]]. - Perform ?
CreatePerIterationEnvironment (perIterationBindings). - Ifincrement is not
empty , then- LetincRef be ?
Evaluation ofincrement. - Perform ?
GetValue (incRef).
- LetincRef be ?
- Iftest is not
14.7.4.4 CreatePerIterationEnvironment (perIterationBindings )
The abstract operation CreatePerIterationEnvironment takes argumentperIterationBindings (a
- IfperIterationBindings has any elements, then
- LetlastIterationEnv be the
running execution context 's LexicalEnvironment. - Letouter belastIterationEnv.[[OuterEnv]].
Assert :outer is notnull .- LetthisIterationEnv be
NewDeclarativeEnvironment (outer). - For each elementbn ofperIterationBindings, do
- Perform ! thisIterationEnv.CreateMutableBinding(bn,
false ). - LetlastValue be ? lastIterationEnv.GetBindingValue(bn,
true ). - Perform ! thisIterationEnv.InitializeBinding(bn,lastValue).
- Perform ! thisIterationEnv.CreateMutableBinding(bn,
- Set the
running execution context 's LexicalEnvironment tothisIterationEnv.
- LetlastIterationEnv be the
- Return
unused .
14.7.5 Thefor-in,for-of, andfor-await-of Statements
Syntax
This section is extended by Annex
14.7.5.1 Static Semantics: Early Errors
- It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply this rule if the extension specified in
If
If
- It is a Syntax Error if
AssignmentTargetType ofLeftHandSideExpression is notsimple .
- It is a Syntax Error if the
BoundNames ofForDeclaration contains"let" . - It is a Syntax Error if any element of the
BoundNames ofForDeclaration also occurs in theVarDeclaredNames ofStatement . - It is a Syntax Error if the
BoundNames ofForDeclaration contains any duplicate entries.
14.7.5.2 Static Semantics: IsDestructuring
The
- If
PrimaryExpression is either anObjectLiteral or anArrayLiteral , returntrue . - Return
false .
- Return
false .
- Return
IsDestructuring ofForBinding .
- Return
false .
- Return
true .
This section is extended by Annex
14.7.5.3 Runtime Semantics: ForDeclarationBindingInitialization
The
var statements and the formal parameter lists of some
It is defined piecewise over the following productions:
- Return ?
BindingInitialization ofForBinding with argumentsvalue andenvironment.
14.7.5.4 Runtime Semantics: ForDeclarationBindingInstantiation
The
- For each elementname of the
BoundNames ofForBinding , do- If
IsConstantDeclaration ofLetOrConst istrue , then- Perform ! environment.CreateImmutableBinding(name,
true ).
- Perform ! environment.CreateImmutableBinding(name,
- Else,
- Perform ! environment.CreateMutableBinding(name,
false ).
- Perform ! environment.CreateMutableBinding(name,
- If
- Return
unused .
14.7.5.5 Runtime Semantics: ForInOfLoopEvaluation
The
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement ,keyResult,enumerate ,assignment ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement ,keyResult,enumerate ,var-binding ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement ,keyResult,enumerate ,lexical-binding ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement ,keyResult,iterate ,assignment ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement ,keyResult,iterate ,var-binding ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement ,keyResult,iterate ,lexical-binding ,labelSet).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (LeftHandSideExpression ,Statement ,keyResult,iterate ,assignment ,labelSet,async ).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForBinding ,Statement ,keyResult,iterate ,var-binding ,labelSet,async ).
- LetkeyResult be ?
ForIn/OfHeadEvaluation (BoundNames ofForDeclaration ,AssignmentExpression ,async-iterate ). - Return ?
ForIn/OfBodyEvaluation (ForDeclaration ,Statement ,keyResult,iterate ,lexical-binding ,labelSet,async ).
This section is extended by Annex
14.7.5.6 ForIn/OfHeadEvaluation (uninitializedBoundNames,expr,iterationKind )
The abstract operation ForIn/OfHeadEvaluation takes argumentsuninitializedBoundNames (a
- LetoldEnv be the
running execution context 's LexicalEnvironment. - IfuninitializedBoundNames is not empty, then
Assert :uninitializedBoundNames has no duplicate entries.- LetnewEnv be
NewDeclarativeEnvironment (oldEnv). - For each Stringname ofuninitializedBoundNames, do
- Perform ! newEnv.CreateMutableBinding(name,
false ).
- Perform ! newEnv.CreateMutableBinding(name,
- Set the
running execution context 's LexicalEnvironment tonewEnv.
- LetexprRef be
Completion (Evaluation ofexpr). - Set the
running execution context 's LexicalEnvironment tooldEnv. - LetexprValue be ?
GetValue (?exprRef). - IfiterationKind is
enumerate , then- IfexprValue is either
undefined ornull , then- Return
Completion Record {[[Type]]:break ,[[Value]]:empty ,[[Target]]:empty }.
- Return
- Letobj be !
ToObject (exprValue). - Letiterator be
EnumerateObjectProperties (obj). - LetnextMethod be !
GetV (iterator,"next" ). - Return the
Iterator Record {[[Iterator]]:iterator,[[NextMethod]]:nextMethod,[[Done]]:false }.
- IfexprValue is either
- Else,
Assert :iterationKind is eitheriterate orasync-iterate .- IfiterationKind is
async-iterate , letiteratorKind beasync . - Else, letiteratorKind be
sync . - Return ?
GetIterator (exprValue,iteratorKind).
14.7.5.7 ForIn/OfBodyEvaluation (lhs,stmt,iteratorRecord,iterationKind,lhsKind,labelSet [ ,iteratorKind ] )
The abstract operation ForIn/OfBodyEvaluation takes argumentslhs (a
- IfiteratorKind is not present, setiteratorKind to
sync . - LetoldEnv be the
running execution context 's LexicalEnvironment. - LetV be
undefined . - Letdestructuring be
IsDestructuring oflhs. - Ifdestructuring is
true andlhsKind isassignment , thenAssert :lhs is aLeftHandSideExpression .- LetassignmentPattern be the
AssignmentPattern that iscovered bylhs.
- Repeat,
- LetnextResult be ?
Call (iteratorRecord.[[NextMethod]],iteratorRecord.[[Iterator]]). - IfiteratorKind is
async , setnextResult to ?Await (nextResult). - IfnextResult
is not an Object , throw aTypeError exception. - Letdone be ?
IteratorComplete (nextResult). - Ifdone is
true , returnV. - LetnextValue be ?
IteratorValue (nextResult). - IflhsKind is either
assignment orvar-binding , then- Ifdestructuring is
true , then- IflhsKind is
assignment , then- Letstatus be
Completion (DestructuringAssignmentEvaluation ofassignmentPattern with argumentnextValue).
- Letstatus be
- Else,
Assert :lhsKind isvar-binding .Assert :lhs is aForBinding .- Letstatus be
Completion (BindingInitialization oflhs with argumentsnextValue andundefined ).
- IflhsKind is
- Else,
- LetlhsRef be
Completion (Evaluation oflhs). (It may be evaluated repeatedly.) - IflhsRef is an
abrupt completion , then- Letstatus belhsRef.
- Else,
- Letstatus be
Completion (PutValue (lhsRef.[[Value]],nextValue)).
- Letstatus be
- LetlhsRef be
- Ifdestructuring is
- Else,
Assert :lhsKind islexical-binding .Assert :lhs is aForDeclaration .- LetiterationEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
ForDeclarationBindingInstantiation oflhs with argumentiterationEnv. - Set the
running execution context 's LexicalEnvironment toiterationEnv. - Ifdestructuring is
true , then- Letstatus be
Completion (ForDeclarationBindingInitialization oflhs with argumentsnextValue anditerationEnv).
- Letstatus be
- Else,
Assert :lhs binds a single name.- LetlhsName be the sole element of
BoundNames oflhs. - LetlhsRef be !
ResolveBinding (lhsName). - Letstatus be
Completion (InitializeReferencedBinding (lhsRef,nextValue)).
- Ifstatus is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment tooldEnv. - IfiteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord,status). - IfiterationKind is
enumerate , then- Return ? status.
- Else,
Assert :iterationKind isiterate .- Return ?
IteratorClose (iteratorRecord,status).
- Set the
- Letresult be
Completion (Evaluation ofstmt). - Set the
running execution context 's LexicalEnvironment tooldEnv. - If
LoopContinues (result,labelSet) isfalse , then- IfiterationKind is
enumerate , then- Return ?
UpdateEmpty (result,V).
- Return ?
- Else,
Assert :iterationKind isiterate .- Setstatus to
Completion (UpdateEmpty (result,V)). - IfiteratorKind is
async , return ?AsyncIteratorClose (iteratorRecord,status). - Return ?
IteratorClose (iteratorRecord,status).
- IfiterationKind is
- Ifresult.[[Value]] is not
empty , setV toresult.[[Value]].
- LetnextResult be ?
14.7.5.8 Runtime Semantics: Evaluation
- LetbindingId be
StringValue ofBindingIdentifier . - Return ?
ResolveBinding (bindingId).
14.7.5.9 EnumerateObjectProperties (O )
The abstract operation EnumerateObjectProperties takes argumentO (an Object) and returns an Iterator. It performs the following steps when called:
- Return an Iterator object (
27.1.1.2 ) whosenextmethod iterates over all the String-valued keys of enumerable properties ofO. The iterator object is never directly accessible to ECMAScript code. The mechanics and order of enumerating the properties is not specified but must conform to the rules specified below.
The iterator'sthrow andreturn methods arenext method processes object properties to determine whether thenext method is ignored. If new properties are added to the target object during enumeration, the newly added properties are not guaranteed to be processed in the active enumeration. Anext method at most once in any enumeration.
Enumerating the properties of the target object includes enumerating properties of its prototype, and the prototype of the prototype, and so on, recursively; but a property of a prototype is not processed if it has the same name as a property that has already been processed by the iterator'snext method. The values of[[Enumerable]] attributes are not considered when determining if a property of a prototype object has already been processed. The enumerable property names of prototype objects must be obtained by invoking EnumerateObjectProperties passing the prototype object as the argument. EnumerateObjectProperties must obtain the own
In addition, if neitherO nor any object in its prototype chain is a
- the value of the[[Prototype]] internal slot ofO or an object in its prototype chain changes,
- a property is removed fromO or an object in its prototype chain,
- a property is added to an object inO's prototype chain, or
- the value of the[[Enumerable]] attribute of a property ofO or an object in its prototype chain changes.
ECMAScript implementations are not required to implement the algorithm in
The following is an informative definition of an ECMAScript generator function that conforms to these rules:
function*EnumerateObjectProperties(obj) {const visited =newSet();for (const keyofReflect.ownKeys(obj)) {if (typeof key ==="symbol")continue;const desc =Reflect.getOwnPropertyDescriptor(obj, key);if (desc) { visited.add(key);if (desc.enumerable)yield key; } }const proto =Reflect.getPrototypeOf(obj);if (proto ===null)return;for (const protoKeyofEnumerateObjectProperties(proto)) {if (!visited.has(protoKey))yield protoKey; }}14.7.5.10 For-In Iterator Objects
A For-In Iterator is an object that represents a specific iteration over some specific object. For-In Iterator objects are never directly accessible to ECMAScript code; they exist solely to illustrate the behaviour of
14.7.5.10.1 CreateForInIterator (object )
The abstract operation CreateForInIterator takes argumentobject (an Object) and returns a For-In Iterator. It is used to create a For-In Iterator object which iterates over the own and inherited enumerable string properties ofobject in a specific order. It performs the following steps when called:
- Letiterator be
OrdinaryObjectCreate (%ForInIteratorPrototype% , «[[Object]],[[ObjectWasVisited]],[[VisitedKeys]],[[RemainingKeys]] »). - Setiterator.[[Object]] toobject.
- Setiterator.[[ObjectWasVisited]] to
false . - Setiterator.[[VisitedKeys]] to a new empty
List . - Setiterator.[[RemainingKeys]] to a new empty
List . - Returniterator.
14.7.5.10.2 The %ForInIteratorPrototype% Object
The%ForInIteratorPrototype% object:
- has properties that are inherited by all For-In Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - is never directly accessible to ECMAScript code.
- has the following properties:
14.7.5.10.2.1 %ForInIteratorPrototype%.next ( )
- LetO be the
this value. Assert :Ois an Object .Assert :O has all of the internal slots of a For-In Iterator Instance (14.7.5.10.3 ).- Letobject beO.[[Object]].
- Repeat,
- IfO.[[ObjectWasVisited]] is
false , then- Letkeys be ? object.[[OwnPropertyKeys]]().
- For each elementkey ofkeys, do
- Ifkey
is a String , then- Appendkey toO.[[RemainingKeys]].
- Ifkey
- SetO.[[ObjectWasVisited]] to
true .
- Repeat, whileO.[[RemainingKeys]] is not empty,
- Letr be the first element ofO.[[RemainingKeys]].
- Remove the first element fromO.[[RemainingKeys]].
- If there does not exist an elementv ofO.[[VisitedKeys]] such that
SameValue (r,v) istrue , then- Letdesc be ? object.[[GetOwnProperty]](r).
- Ifdesc is not
undefined , then- Appendr toO.[[VisitedKeys]].
- Ifdesc.[[Enumerable]] is
true , returnCreateIterResultObject (r,false ).
- Setobject to ? object.[[GetPrototypeOf]]().
- SetO.[[Object]] toobject.
- SetO.[[ObjectWasVisited]] to
false . - Ifobject is
null , returnCreateIterResultObject (undefined ,true ).
- IfO.[[ObjectWasVisited]] is
14.7.5.10.3 Properties of For-In Iterator Instances
For-In Iterator instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[Object]] | an Object | The Object value whose properties are being iterated. |
| [[ObjectWasVisited]] | a Boolean | |
| [[VisitedKeys]] | a | The values that have been emitted by this iterator thus far. |
| [[RemainingKeys]] | a | The values remaining to be emitted for the current object, before iterating the properties of its prototype (if its prototype is not |
14.8 Thecontinue Statement
Syntax
14.8.1 Static Semantics: Early Errors
- It is a Syntax Error if this
ContinueStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement .
14.8.2 Runtime Semantics: Evaluation
- Return
Completion Record {[[Type]]:continue ,[[Value]]:empty ,[[Target]]:empty }.
- Letlabel be the
StringValue ofLabelIdentifier . - Return
Completion Record {[[Type]]:continue ,[[Value]]:empty ,[[Target]]:label }.
14.9 Thebreak Statement
Syntax
14.9.1 Static Semantics: Early Errors
- It is a Syntax Error if this
BreakStatement is not nested, directly or indirectly (but not crossing function orstaticinitialization block boundaries), within anIterationStatement or aSwitchStatement .
14.9.2 Runtime Semantics: Evaluation
- Return
Completion Record {[[Type]]:break ,[[Value]]:empty ,[[Target]]:empty }.
- Letlabel be the
StringValue ofLabelIdentifier . - Return
Completion Record {[[Type]]:break ,[[Value]]:empty ,[[Target]]:label }.
14.10 Thereturn Statement
Syntax
Areturn statement causes a function to cease execution and, in most cases, returns a value to the caller. Ifreturn statement may not actually return a value to the caller depending on surrounding context. For example, in atry block, areturn statement'sfinally block.
14.10.1 Runtime Semantics: Evaluation
- Return
Completion Record {[[Type]]:return ,[[Value]]:undefined ,[[Target]]:empty }.
- LetexprRef be ?
Evaluation ofExpression . - LetexprValue be ?
GetValue (exprRef). - If
GetGeneratorKind () isasync , setexprValue to ?Await (exprValue). - Return
Completion Record {[[Type]]:return ,[[Value]]:exprValue,[[Target]]:empty }.
14.11 Thewith Statement
Use of thewith statement is discouraged in new ECMAScript code. Consider alternatives that are permitted in both
Syntax
Thewith statement adds an
14.11.1 Static Semantics: Early Errors
- It is a Syntax Error if the
source text matched by this production is contained instrict mode code . - It is a Syntax Error if
IsLabelledFunction (Statement ) istrue .
It is only necessary to apply the second rule if the extension specified in
14.11.2 Runtime Semantics: Evaluation
- Letval be ?
Evaluation ofExpression . - Letobj be ?
ToObject (?GetValue (val)). - LetoldEnv be the
running execution context 's LexicalEnvironment. - LetnewEnv be
NewObjectEnvironment (obj,true ,oldEnv). - Set the
running execution context 's LexicalEnvironment tonewEnv. - LetC be
Completion (Evaluation ofStatement ). - Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ?
UpdateEmpty (C,undefined ).
No matter how control leaves the embedded
14.12 Theswitch Statement
Syntax
14.12.1 Static Semantics: Early Errors
- It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
14.12.2 Runtime Semantics: CaseBlockEvaluation
The
- Return
undefined .
- LetV be
undefined . - LetA be the
List ofCaseClause items inCaseClauses , in source text order. - Letfound be
false . - For each
CaseClause C ofA, do- Iffound is
false , then- Setfound to ?
CaseClauseIsSelected (C,input).
- Setfound to ?
- Iffound is
true , then- LetR be
Completion (Evaluation ofC). - IfR.[[Value]] is not
empty , setV toR.[[Value]]. - IfR is an
abrupt completion , return ?UpdateEmpty (R,V).
- LetR be
- Iffound is
- ReturnV.
- LetV be
undefined . - If the first
CaseClauses is present, then- LetA be the
List ofCaseClause items in the firstCaseClauses , in source text order.
- LetA be the
- Else,
- LetA be a new empty
List .
- LetA be a new empty
- Letfound be
false . - For each
CaseClause C ofA, do- Iffound is
false , then- Setfound to ?
CaseClauseIsSelected (C,input).
- Setfound to ?
- Iffound is
true , then- LetR be
Completion (Evaluation ofC). - IfR.[[Value]] is not
empty , setV toR.[[Value]]. - IfR is an
abrupt completion , return ?UpdateEmpty (R,V).
- LetR be
- Iffound is
- LetfoundInB be
false . - If the second
CaseClauses is present, then- LetB be the
List ofCaseClause items in the secondCaseClauses , in source text order.
- LetB be the
- Else,
- LetB be a new empty
List .
- LetB be a new empty
- Iffound is
false , then- For each
CaseClause C ofB, do- IffoundInB is
false , then- SetfoundInB to ?
CaseClauseIsSelected (C,input).
- SetfoundInB to ?
- IffoundInB is
true , then- LetR be
Completion (Evaluation ofCaseClause C). - IfR.[[Value]] is not
empty , setV toR.[[Value]]. - IfR is an
abrupt completion , return ?UpdateEmpty (R,V).
- LetR be
- IffoundInB is
- For each
- IffoundInB is
true , returnV. - LetdefaultR be
Completion (Evaluation ofDefaultClause ). - IfdefaultR.[[Value]] is not
empty , setV todefaultR.[[Value]]. - IfdefaultR is an
abrupt completion , return ?UpdateEmpty (defaultR,V). - NOTE: The following is another complete iteration of the second
CaseClauses . - For each
CaseClause C ofB, do- LetR be
Completion (Evaluation ofCaseClause C). - IfR.[[Value]] is not
empty , setV toR.[[Value]]. - IfR is an
abrupt completion , return ?UpdateEmpty (R,V).
- LetR be
- ReturnV.
14.12.3 CaseClauseIsSelected (C,input )
The abstract operation CaseClauseIsSelected takes argumentsC (a
Assert :C is an instance of the productionCaseClause : case Expression : StatementList opt - LetexprRef be ?
Evaluation of theExpression ofC. - LetclauseSelector be ?
GetValue (exprRef). - Return
IsStrictlyEqual (input,clauseSelector).
This operation does not executeC's
14.12.4 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofExpression . - LetswitchValue be ?
GetValue (exprRef). - LetoldEnv be the
running execution context 's LexicalEnvironment. - LetblockEnv be
NewDeclarativeEnvironment (oldEnv). - Perform
BlockDeclarationInstantiation (CaseBlock ,blockEnv). - Set the
running execution context 's LexicalEnvironment toblockEnv. - LetR be
Completion (CaseBlockEvaluation ofCaseBlock with argumentswitchValue). - Set the
running execution context 's LexicalEnvironment tooldEnv. - ReturnR.
No matter how control leaves the
- Return
empty .
- Return ?
Evaluation ofStatementList .
- Return
empty .
- Return ?
Evaluation ofStatementList .
14.13 Labelled Statements
Syntax
Abreak andcontinue statements. ECMAScript has nogoto statement. A
14.13.1 Static Semantics: Early Errors
- It is a Syntax Error if any source text is matched by this production.
An alternative definition for this rule is provided in
14.13.2 Static Semantics: IsLabelledFunction (stmt )
The abstract operation IsLabelledFunction takes argumentstmt (a
- Ifstmt is not a
LabelledStatement , returnfalse . - Letitem be the
LabelledItem ofstmt. - Ifitem is
LabelledItem : FunctionDeclaration true . - LetsubStmt be the
Statement ofitem. - Return
IsLabelledFunction (subStmt).
14.13.3 Runtime Semantics: Evaluation
- Return ?
LabelledEvaluation of thisLabelledStatement with argument « ».
14.13.4 Runtime Semantics: LabelledEvaluation
The
- LetstmtResult be
Completion (LoopEvaluation ofIterationStatement with argumentlabelSet). - IfstmtResult is a
break completion , then- IfstmtResult.[[Target]] is
empty , then- IfstmtResult.[[Value]] is
empty , setstmtResult toNormalCompletion (undefined ). - Else, setstmtResult to
NormalCompletion (stmtResult.[[Value]]).
- IfstmtResult.[[Value]] is
- IfstmtResult.[[Target]] is
- Return ? stmtResult.
- LetstmtResult be
Completion (Evaluation ofSwitchStatement ). - IfstmtResult is a
break completion , then- IfstmtResult.[[Target]] is
empty , then- IfstmtResult.[[Value]] is
empty , setstmtResult toNormalCompletion (undefined ). - Else, setstmtResult to
NormalCompletion (stmtResult.[[Value]]).
- IfstmtResult.[[Value]] is
- IfstmtResult.[[Target]] is
- Return ? stmtResult.
A
- Letlabel be the
StringValue ofLabelIdentifier . - LetnewLabelSet be the
list-concatenation oflabelSet and «label ». - LetstmtResult be
Completion (LabelledEvaluation ofLabelledItem with argumentnewLabelSet). - IfstmtResult is a
break completion andstmtResult.[[Target]] islabel, then- SetstmtResult to
NormalCompletion (stmtResult.[[Value]]).
- SetstmtResult to
- Return ? stmtResult.
- Return ?
Evaluation ofFunctionDeclaration .
- Return ?
Evaluation ofStatement .
The only two productions of
14.14 Thethrow Statement
Syntax
14.14.1 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofExpression . - LetexprValue be ?
GetValue (exprRef). - Return
ThrowCompletion (exprValue).
14.15 Thetry Statement
Syntax
Thetry statement encloses a block of code in which an exceptional condition can occur, such as a runtime error or athrow statement. Thecatch clause provides the exception-handling code. When a catch clause catches an exception, its
14.15.1 Static Semantics: Early Errors
- It is a Syntax Error if
BoundNames ofCatchParameter contains any duplicate elements. - It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . - It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock .
An alternative
14.15.2 Runtime Semantics: CatchClauseEvaluation
The
- LetoldEnv be the
running execution context 's LexicalEnvironment. - LetcatchEnv be
NewDeclarativeEnvironment (oldEnv). - For each elementargName of the
BoundNames ofCatchParameter , do- Perform ! catchEnv.CreateMutableBinding(argName,
false ).
- Perform ! catchEnv.CreateMutableBinding(argName,
- Set the
running execution context 's LexicalEnvironment tocatchEnv. - Letstatus be
Completion (BindingInitialization ofCatchParameter with argumentsthrownValue andcatchEnv). - Ifstatus is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ? status.
- Set the
- LetB be
Completion (Evaluation ofBlock ). - Set the
running execution context 's LexicalEnvironment tooldEnv. - Return ? B.
- Return ?
Evaluation ofBlock .
No matter how control leaves the
14.15.3 Runtime Semantics: Evaluation
- LetB be
Completion (Evaluation ofBlock ). - IfB is a
throw completion , letC beCompletion (CatchClauseEvaluation ofCatch with argumentB.[[Value]]). - Else, letC beB.
- Return ?
UpdateEmpty (C,undefined ).
- LetB be
Completion (Evaluation ofBlock ). - LetF be
Completion (Evaluation ofFinally ). - IfF is a
normal completion , setF toB. - Return ?
UpdateEmpty (F,undefined ).
- LetB be
Completion (Evaluation ofBlock ). - IfB is a
throw completion , letC beCompletion (CatchClauseEvaluation ofCatch with argumentB.[[Value]]). - Else, letC beB.
- LetF be
Completion (Evaluation ofFinally ). - IfF is a
normal completion , setF toC. - Return ?
UpdateEmpty (F,undefined ).
14.16 Thedebugger Statement
Syntax
14.16.1 Runtime Semantics: Evaluation
Evaluating a
- If an
implementation-defined debugging facility is available and enabled, then- Perform an
implementation-defined debugging action. - Return a new
implementation-defined Completion Record .
- Perform an
- Else,
- Return
empty .
- Return
15 ECMAScript Language: Functions and Classes
Various ECMAScript language elements cause the creation of ECMAScript
15.1 Parameter Lists
Syntax
15.1.1 Static Semantics: Early Errors
- It is a Syntax Error if
BoundNames ofFormalParameters contains any duplicate elements.
- It is a Syntax Error if
IsSimpleParameterList ofFormalParameterList isfalse andBoundNames ofFormalParameterList contains any duplicate elements.
Multiple occurrences of the same
15.1.2 Static Semantics: ContainsExpression
The
- Return
false .
- Return
ContainsExpression ofBindingPropertyList .
- Return
false .
- Return
ContainsExpression ofBindingRestElement .
- Return
ContainsExpression ofBindingElementList .
- Lethas be
ContainsExpression ofBindingElementList . - Ifhas is
true , returntrue . - Return
ContainsExpression ofBindingRestElement .
- Lethas be
ContainsExpression ofBindingPropertyList . - Ifhas is
true , returntrue . - Return
ContainsExpression ofBindingProperty .
- Lethas be
ContainsExpression ofBindingElementList . - Ifhas is
true , returntrue . - Return
ContainsExpression ofBindingElisionElement .
- Return
ContainsExpression ofBindingElement .
- Lethas be
IsComputedPropertyKey ofPropertyName . - Ifhas is
true , returntrue . - Return
ContainsExpression ofBindingElement .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
ContainsExpression ofBindingPattern .
- Return
false .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFunctionRestParameter .
- If
ContainsExpression ofFormalParameterList istrue , returntrue . - Return
ContainsExpression ofFormalParameter .
- Return
false .
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
ContainsExpression offormals.
- Return
false .
15.1.3 Static Semantics: IsSimpleParameterList
The
- Return
false .
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
false .
- Return
false .
- If
IsSimpleParameterList ofFormalParameterList isfalse , returnfalse . - Return
IsSimpleParameterList ofFormalParameter .
- Return
IsSimpleParameterList ofBindingElement .
- Return
true .
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
IsSimpleParameterList offormals.
- Return
true .
- Lethead be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Return
IsSimpleParameterList ofhead.
15.1.4 Static Semantics: HasInitializer
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- If
HasInitializer ofFormalParameterList istrue , returntrue . - Return
HasInitializer ofFormalParameter .
15.1.5 Static Semantics: ExpectedArgumentCount
The
- Return 0.
- Return
ExpectedArgumentCount ofFormalParameterList .
The ExpectedArgumentCount of a
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Letcount be
ExpectedArgumentCount ofFormalParameterList . - If
HasInitializer ofFormalParameterList istrue orHasInitializer ofFormalParameter istrue , returncount. - Returncount + 1.
- Return 1.
- Letformals be the
ArrowFormalParameters that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
ExpectedArgumentCount offormals.
- If
HasInitializer ofFormalParameter istrue , return 0. - Return 1.
- Return 1.
15.2 Function Definitions
Syntax
15.2.1 Static Semantics: Early Errors
- If the
source text matched by FormalParameters isstrict mode code , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present and thesource text matched by BindingIdentifier isstrict mode code , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
FunctionBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
FunctionBody Contains SuperCall istrue .
The
- It is a Syntax Error if the
LexicallyDeclaredNames ofFunctionStatementList contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofFunctionStatementList also occurs in theVarDeclaredNames ofFunctionStatementList . - It is a Syntax Error if
ContainsDuplicateLabels ofFunctionStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedBreakTarget ofFunctionStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedContinueTarget ofFunctionStatementList with arguments « » and « » istrue .
15.2.2 Static Semantics: FunctionBodyContainsUseStrict
The
- If the
Directive Prologue ofFunctionBody contains aUse Strict Directive , returntrue ; otherwise, returnfalse .
15.2.3 Runtime Semantics: EvaluateFunctionBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject,argumentsList). - Return ?
Evaluation ofFunctionStatementList .
15.2.4 Runtime Semantics: InstantiateOrdinaryFunctionObject
The
- Letname be
StringValue ofBindingIdentifier . - LetsourceText be the
source text matched by FunctionDeclaration . - LetF be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,FormalParameters ,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,name). - Perform
MakeConstructor (F). - ReturnF.
- LetsourceText be the
source text matched by FunctionDeclaration . - LetF be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,FormalParameters ,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,"default" ). - Perform
MakeConstructor (F). - ReturnF.
An anonymousexport default declaration, and its function code is therefore always
15.2.5 Runtime Semantics: InstantiateOrdinaryFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by FunctionExpression . - Letclosure be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,FormalParameters ,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Perform
MakeConstructor (closure). - Returnclosure.
Assert :name is not present.- Setname to
StringValue ofBindingIdentifier . - LetouterEnv be the
running execution context 's LexicalEnvironment. - LetfuncEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by FunctionExpression . - Letclosure be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,FormalParameters ,FunctionBody ,non-lexical-this ,funcEnv,privateEnv). - Perform
SetFunctionName (closure,name). - Perform
MakeConstructor (closure). - Perform ! funcEnv.InitializeBinding(name,closure).
- Returnclosure.
The
15.2.6 Runtime Semantics: Evaluation
- Return
empty .
An alternative semantics is provided in
- Return
empty .
A
- Return
undefined .
15.3 Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.3.1 Static Semantics: Early Errors
- It is a Syntax Error if
ArrowParameters Contains YieldExpression istrue . - It is a Syntax Error if
ArrowParameters Contains AwaitExpression istrue . - It is a Syntax Error if
ConciseBodyContainsUseStrict ofConciseBody istrue andIsSimpleParameterList ofArrowParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofArrowParameters also occurs in theLexicallyDeclaredNames ofConciseBody .
15.3.2 Static Semantics: ConciseBodyContainsUseStrict
The
- Return
false .
15.3.3 Runtime Semantics: EvaluateConciseBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject,argumentsList). - Return ?
Evaluation ofExpressionBody .
15.3.4 Runtime Semantics: InstantiateArrowFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by ArrowFunction . - Letclosure be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,ArrowParameters ,ConciseBody ,lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Returnclosure.
Anarguments,super,this, ornew.target. Any reference toarguments,super,this, ornew.target within ansuper, thesuper is always contained within a non-super is accessible via theenv that is captured by the
15.3.5 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofAssignmentExpression . - LetexprValue be ?
GetValue (exprRef). - Return
Completion Record {[[Type]]:return ,[[Value]]:exprValue,[[Target]]:empty }.
15.4 Method Definitions
Syntax
15.4.1 Static Semantics: Early Errors
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofFunctionBody .
- It is a Syntax Error if
BoundNames ofPropertySetParameterList contains any duplicate elements. - It is a Syntax Error if
FunctionBodyContainsUseStrict ofFunctionBody istrue andIsSimpleParameterList ofPropertySetParameterList isfalse . - It is a Syntax Error if any element of the
BoundNames ofPropertySetParameterList also occurs in theLexicallyDeclaredNames ofFunctionBody .
15.4.2 Static Semantics: HasDirectSuper
The
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- If
PropertySetParameterList Contains SuperCall istrue , returntrue . - Return
FunctionBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
GeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncGeneratorBody Contains SuperCall .
- If
UniqueFormalParameters Contains SuperCall istrue , returntrue . - Return
AsyncFunctionBody Contains SuperCall .
15.4.3 Static Semantics: SpecialMethod
The
- Return
false .
- Return
true .
15.4.4 Runtime Semantics: DefineMethod
The
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - IffunctionPrototype is present, then
- Letprototype befunctionPrototype.
- Else,
- Letprototype be
%Function.prototype% .
- Letprototype be
- LetsourceText be the
source text matched by MethodDefinition . - Letclosure be
OrdinaryFunctionCreate (prototype,sourceText,UniqueFormalParameters ,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Return the
Record {[[Key]]:propKey,[[Closure]]:closure }.
15.4.5 Runtime Semantics: MethodDefinitionEvaluation
The
- LetmethodDef be ?
DefineMethod ofMethodDefinition with argumentobject. - Perform
SetFunctionName (methodDef.[[Closure]],methodDef.[[Key]]). - Return ?
DefineMethodProperty (object,methodDef.[[Key]],methodDef.[[Closure]],enumerable).
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by MethodDefinition . - LetformalParameterList be an instance of the production
FormalParameters : [empty] - Letclosure be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,formalParameterList,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Perform
SetFunctionName (closure,propKey,"get" ). - IfpropKey is a
Private Name , then- Return
PrivateElement {[[Key]]:propKey,[[Kind]]:accessor ,[[Get]]:closure,[[Set]]:undefined }.
- Return
- Else,
- Letdesc be the PropertyDescriptor {[[Get]]:closure,[[Enumerable]]:enumerable,[[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object,propKey,desc). - Return
unused .
- Letdesc be the PropertyDescriptor {[[Get]]:closure,[[Enumerable]]:enumerable,[[Configurable]]:
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by MethodDefinition . - Letclosure be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,PropertySetParameterList ,FunctionBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Perform
SetFunctionName (closure,propKey,"set" ). - IfpropKey is a
Private Name , then- Return
PrivateElement {[[Key]]:propKey,[[Kind]]:accessor ,[[Get]]:undefined ,[[Set]]:closure }.
- Return
- Else,
- Letdesc be the PropertyDescriptor {[[Set]]:closure,[[Enumerable]]:enumerable,[[Configurable]]:
true }. - Perform ?
DefinePropertyOrThrow (object,propKey,desc). - Return
unused .
- Letdesc be the PropertyDescriptor {[[Set]]:closure,[[Enumerable]]:enumerable,[[Configurable]]:
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by GeneratorMethod . - Letclosure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% ,sourceText,UniqueFormalParameters ,GeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Perform
SetFunctionName (closure,propKey). - Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Return ?
DefineMethodProperty (object,propKey,closure,enumerable).
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncGeneratorMethod . - Letclosure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% ,sourceText,UniqueFormalParameters ,AsyncGeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Perform
SetFunctionName (closure,propKey). - Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Return ?
DefineMethodProperty (object,propKey,closure,enumerable).
- LetpropKey be ?
Evaluation ofClassElementName . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncMethod . - Letclosure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,UniqueFormalParameters ,AsyncFunctionBody ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (closure,object). - Perform
SetFunctionName (closure,propKey). - Return ?
DefineMethodProperty (object,propKey,closure,enumerable).
15.5 Generator Function Definitions
Syntax
The syntactic context immediately followingyield requires use of the
15.5.1 Static Semantics: Early Errors
- It is a Syntax Error if
HasDirectSuper ofGeneratorMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody .
- If the
source text matched by FormalParameters isstrict mode code , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present and thesource text matched by BindingIdentifier isstrict mode code , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofGeneratorBody . - It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
GeneratorBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
GeneratorBody Contains SuperCall istrue .
15.5.2 Runtime Semantics: EvaluateGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject,argumentsList). - LetG be ?
OrdinaryCreateFromConstructor (functionObject,"%GeneratorFunction.prototype.prototype%" , «[[GeneratorState]],[[GeneratorContext]],[[GeneratorBrand]] »). - SetG.[[GeneratorBrand]] to
empty . - Perform
GeneratorStart (G,FunctionBody ). - Return
Completion Record {[[Type]]:return ,[[Value]]:G,[[Target]]:empty }.
15.5.3 Runtime Semantics: InstantiateGeneratorFunctionObject
The
- Letname be
StringValue ofBindingIdentifier . - LetsourceText be the
source text matched by GeneratorDeclaration . - LetF be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% ,sourceText,FormalParameters ,GeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,name). - Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnF.
- LetsourceText be the
source text matched by GeneratorDeclaration . - LetF be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% ,sourceText,FormalParameters ,GeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,"default" ). - Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnF.
An anonymousexport default declaration, and its function code is therefore always
15.5.4 Runtime Semantics: InstantiateGeneratorFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by GeneratorExpression . - Letclosure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% ,sourceText,FormalParameters ,GeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Returnclosure.
Assert :name is not present.- Setname to
StringValue ofBindingIdentifier . - LetouterEnv be the
running execution context 's LexicalEnvironment. - LetfuncEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by GeneratorExpression . - Letclosure be
OrdinaryFunctionCreate (%GeneratorFunction.prototype% ,sourceText,FormalParameters ,GeneratorBody ,non-lexical-this ,funcEnv,privateEnv). - Perform
SetFunctionName (closure,name). - Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name,closure).
- Returnclosure.
The
15.5.5 Runtime Semantics: Evaluation
- Return ?
Yield (undefined ).
- LetexprRef be ?
Evaluation ofAssignmentExpression . - Letvalue be ?
GetValue (exprRef). - Return ?
Yield (value).
- LetgeneratorKind be
GetGeneratorKind (). - LetexprRef be ?
Evaluation ofAssignmentExpression . - Letvalue be ?
GetValue (exprRef). - LetiteratorRecord be ?
GetIterator (value,generatorKind). - Letiterator beiteratorRecord.[[Iterator]].
- Letreceived be
NormalCompletion (undefined ). - Repeat,
- Ifreceived is a
normal completion , then- LetinnerResult be ?
Call (iteratorRecord.[[NextMethod]],iteratorRecord.[[Iterator]], «received.[[Value]] »). - IfgeneratorKind is
async , setinnerResult to ?Await (innerResult). - IfinnerResult
is not an Object , throw aTypeError exception. - Letdone be ?
IteratorComplete (innerResult). - Ifdone is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- IfgeneratorKind is
async , setreceived toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, setreceived to
Completion (GeneratorYield (innerResult)).
- LetinnerResult be ?
- Else ifreceived is a
throw completion , then- Letthrow be ?
GetMethod (iterator,"throw" ). - Ifthrow is not
undefined , then- LetinnerResult be ?
Call (throw,iterator, «received.[[Value]] »). - IfgeneratorKind is
async , setinnerResult to ?Await (innerResult). - NOTE: Exceptions from the inner iterator
throwmethod are propagated.Normal completions from an innerthrowmethod are processed similarly to an innernext. - IfinnerResult
is not an Object , throw aTypeError exception. - Letdone be ?
IteratorComplete (innerResult). - Ifdone is
true , then- Return ?
IteratorValue (innerResult).
- Return ?
- IfgeneratorKind is
async , setreceived toCompletion (AsyncGeneratorYield (?IteratorValue (innerResult))). - Else, setreceived to
Completion (GeneratorYield (innerResult)).
- LetinnerResult be ?
- Else,
- NOTE: Ifiterator does not have a
throwmethod, this throw is going to terminate theyield*loop. But first we need to giveiterator a chance to clean up. - LetcloseCompletion be
Completion Record {[[Type]]:normal ,[[Value]]:empty ,[[Target]]:empty }. - IfgeneratorKind is
async , perform ?AsyncIteratorClose (iteratorRecord,closeCompletion). - Else, perform ?
IteratorClose (iteratorRecord,closeCompletion). - NOTE: The next step throws a
TypeError to indicate that there was ayield*protocol violation:iterator does not have athrowmethod. - Throw a
TypeError exception.
- NOTE: Ifiterator does not have a
- Letthrow be ?
- Else,
Assert :received is areturn completion .- Letreturn be ?
GetMethod (iterator,"return" ). - Ifreturn is
undefined , then- Setvalue toreceived.[[Value]].
- IfgeneratorKind is
async , then- Setvalue to ?
Await (value).
- Setvalue to ?
- Return
Completion Record {[[Type]]:return ,[[Value]]:value,[[Target]]:empty }.
- LetinnerReturnResult be ?
Call (return,iterator, «received.[[Value]] »). - IfgeneratorKind is
async , setinnerReturnResult to ?Await (innerReturnResult). - IfinnerReturnResult
is not an Object , throw aTypeError exception. - Letdone be ?
IteratorComplete (innerReturnResult). - Ifdone is
true , then- Setvalue to ?
IteratorValue (innerReturnResult). - Return
Completion Record {[[Type]]:return ,[[Value]]:value,[[Target]]:empty }.
- Setvalue to ?
- IfgeneratorKind is
async , setreceived toCompletion (AsyncGeneratorYield (?IteratorValue (innerReturnResult))). - Else, setreceived to
Completion (GeneratorYield (innerReturnResult)).
- Ifreceived is a
15.6 Async Generator Function Definitions
Syntax
15.6.1 Static Semantics: Early Errors
- It is a Syntax Error if
HasDirectSuper ofAsyncGeneratorMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody .
- If the
source text matched by FormalParameters isstrict mode code , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present and thesource text matched by BindingIdentifier isstrict mode code , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncGeneratorBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncGeneratorBody . - It is a Syntax Error if
FormalParameters Contains YieldExpression istrue . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncGeneratorBody Contains SuperCall istrue .
15.6.2 Runtime Semantics: EvaluateAsyncGeneratorBody
The
- Perform ?
FunctionDeclarationInstantiation (functionObject,argumentsList). - Letgenerator be ?
OrdinaryCreateFromConstructor (functionObject,"%AsyncGeneratorFunction.prototype.prototype%" , «[[AsyncGeneratorState]],[[AsyncGeneratorContext]],[[AsyncGeneratorQueue]],[[GeneratorBrand]] »). - Setgenerator.[[GeneratorBrand]] to
empty . - Perform
AsyncGeneratorStart (generator,FunctionBody ). - Return
Completion Record {[[Type]]:return ,[[Value]]:generator,[[Target]]:empty }.
15.6.3 Runtime Semantics: InstantiateAsyncGeneratorFunctionObject
The
- Letname be
StringValue ofBindingIdentifier . - LetsourceText be the
source text matched by AsyncGeneratorDeclaration . - LetF be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% ,sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,name). - Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnF.
- LetsourceText be the
source text matched by AsyncGeneratorDeclaration . - LetF be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% ,sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,"default" ). - Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - ReturnF.
An anonymousexport default declaration.
15.6.4 Runtime Semantics: InstantiateAsyncGeneratorFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncGeneratorExpression . - Letclosure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% ,sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Returnclosure.
Assert :name is not present.- Setname to
StringValue ofBindingIdentifier . - LetouterEnv be the
running execution context 's LexicalEnvironment. - LetfuncEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncGeneratorExpression . - Letclosure be
OrdinaryFunctionCreate (%AsyncGeneratorFunction.prototype% ,sourceText,FormalParameters ,AsyncGeneratorBody ,non-lexical-this ,funcEnv,privateEnv). - Perform
SetFunctionName (closure,name). - Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (closure,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Perform ! funcEnv.InitializeBinding(name,closure).
- Returnclosure.
The
15.6.5 Runtime Semantics: Evaluation
15.7 Class Definitions
Syntax
A class definition is always
15.7.1 Static Semantics: Early Errors
It is a Syntax Error if
ClassHeritage is not present and the following algorithm returnstrue :- Letconstructor be
ConstructorMethod ofClassBody . - Ifconstructor is
empty , returnfalse . - Return
HasDirectSuper ofconstructor.
- Letconstructor be
- It is a Syntax Error if
PrototypePropertyNameList ofClassElementList contains more than one occurrence of"constructor" . - It is a Syntax Error if
PrivateBoundIdentifiers ofClassElementList contains any duplicate entries, unless the name is used once for a getter and once for a setter and in no other entries, and the getter and setter are either both static or both non-static.
- It is a Syntax Error if
PropName ofMethodDefinition is not"constructor" andHasDirectSuper ofMethodDefinition istrue . - It is a Syntax Error if
PropName ofMethodDefinition is"constructor" andSpecialMethod ofMethodDefinition istrue .
- It is a Syntax Error if
HasDirectSuper ofMethodDefinition istrue . - It is a Syntax Error if
PropName ofMethodDefinition is"prototype" .
- It is a Syntax Error if
PropName ofFieldDefinition is"constructor" .
- It is a Syntax Error if
PropName ofFieldDefinition is either"prototype" or"constructor" .
- It is a Syntax Error if
Initializer is present andContainsArguments ofInitializer istrue . - It is a Syntax Error if
Initializer is present andInitializer Contains SuperCall istrue .
- It is a Syntax Error if
StringValue ofPrivateIdentifier is"#constructor" .
- It is a Syntax Error if the
LexicallyDeclaredNames ofClassStaticBlockStatementList contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofClassStaticBlockStatementList also occurs in theVarDeclaredNames ofClassStaticBlockStatementList . - It is a Syntax Error if
ContainsDuplicateLabels ofClassStaticBlockStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedBreakTarget ofClassStaticBlockStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedContinueTarget ofClassStaticBlockStatementList with arguments « » and « » istrue . - It is a Syntax Error if
ContainsArguments ofClassStaticBlockStatementList istrue . - It is a Syntax Error if
ClassStaticBlockStatementList Contains SuperCall istrue . - It is a Syntax Error if
ClassStaticBlockStatementList Contains awaitistrue .
15.7.2 Static Semantics: ClassElementKind
The
- If
PropName ofMethodDefinition is"constructor" , returnconstructor-method . - Return
non-constructor-method .
- Return
non-constructor-method .
- Return
non-constructor-method .
- Return
empty .
15.7.3 Static Semantics: ConstructorMethod
The
- If
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
- Lethead be
ConstructorMethod ofClassElementList . - Ifhead is not
empty , returnhead. - If
ClassElementKind ofClassElement isconstructor-method , returnClassElement . - Return
empty .
Early Error rules ensure that there is only one method definition named
15.7.4 Static Semantics: IsStatic
The
- Return
false .
- Return
true .
- Return
false .
- Return
true .
- Return
true .
- Return
false .
15.7.5 Static Semantics: NonConstructorElements
The
- If
ClassElementKind ofClassElement isnon-constructor-method , then- Return «
ClassElement ».
- Return «
- Return a new empty
List .
- Letlist be
NonConstructorElements ofClassElementList . - If
ClassElementKind ofClassElement isnon-constructor-method , then- Append
ClassElement to the end oflist.
- Append
- Returnlist.
15.7.6 Static Semantics: PrototypePropertyNameList
The
- LetpropName be
PropName ofClassElement . - IfpropName is
empty , return a new emptyList . - If
IsStatic ofClassElement istrue , return a new emptyList . - Return «propName ».
- Letlist be
PrototypePropertyNameList ofClassElementList . - LetpropName be
PropName ofClassElement . - IfpropName is
empty , returnlist. - If
IsStatic ofClassElement istrue , returnlist. - Return the
list-concatenation oflist and «propName ».
15.7.7 Static Semantics: AllPrivateIdentifiersValid
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of AllPrivateIdentifiersValid:
- For each child nodechild of this
Parse Node , do- Ifchild is an instance of a nonterminal, then
- If
AllPrivateIdentifiersValid ofchild with argumentnames isfalse , returnfalse .
- If
- Ifchild is an instance of a nonterminal, then
- Return
true .
- Ifnames contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofMemberExpression with argumentnames.
- Return
- Return
false .
- Ifnames contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofCallExpression with argumentnames.
- Return
- Return
false .
- Ifnames contains the
StringValue ofPrivateIdentifier , returntrue . - Return
false .
- Ifnames contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofOptionalChain with argumentnames.
- Return
- Return
false .
- LetnewNames be the
list-concatenation ofnames andPrivateBoundIdentifiers ofClassBody . - Return
AllPrivateIdentifiersValid ofClassElementList with argumentnewNames.
- Ifnames contains the
StringValue ofPrivateIdentifier , then- Return
AllPrivateIdentifiersValid ofShiftExpression with argumentnames.
- Return
- Return
false .
15.7.8 Static Semantics: PrivateBoundIdentifiers
The
- Return
PrivateBoundIdentifiers ofClassElementName .
- Return a
List whose sole element is theStringValue ofPrivateIdentifier .
- Return a new empty
List .
- Letnames1 be
PrivateBoundIdentifiers ofClassElementList . - Letnames2 be
PrivateBoundIdentifiers ofClassElement . - Return the
list-concatenation ofnames1 andnames2.
- Return
PrivateBoundIdentifiers ofClassElementName .
15.7.9 Static Semantics: ContainsArguments
The
Every grammar production alternative in this specification which is not listed below implicitly has the following default definition of ContainsArguments:
- For each child nodechild of this
Parse Node , do- Ifchild is an instance of a nonterminal, then
- If
ContainsArguments ofchild istrue , returntrue .
- If
- Ifchild is an instance of a nonterminal, then
- Return
false .
- If the
StringValue ofIdentifier is"arguments" , returntrue . - Return
false .
- Return
false .
- Return
ContainsArguments ofClassElementName .
15.7.10 Runtime Semantics: ClassFieldDefinitionEvaluation
The
- Letname be ?
Evaluation ofClassElementName . - If
Initializer is present, then- LetformalParameterList be an instance of the production
FormalParameters : [empty] - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the empty sequence of Unicode code points.
- Letinitializer be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,formalParameterList,Initializer ,non-lexical-this ,env,privateEnv). - Perform
MakeMethod (initializer,homeObject). - Setinitializer.[[ClassFieldInitializerName]] toname.
- LetformalParameterList be an instance of the production
- Else,
- Letinitializer be
empty .
- Letinitializer be
- Return the
ClassFieldDefinition Record {[[Name]]:name,[[Initializer]]:initializer }.
15.7.11 Runtime Semantics: ClassStaticBlockDefinitionEvaluation
The
- Letlex be the
running execution context 's LexicalEnvironment. - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the empty sequence of Unicode code points.
- LetformalParameters be an instance of the production
FormalParameters : [empty] - LetbodyFunction be
OrdinaryFunctionCreate (%Function.prototype% ,sourceText,formalParameters,ClassStaticBlockBody ,non-lexical-this ,lex,privateEnv). - Perform
MakeMethod (bodyFunction,homeObject). - Return the
ClassStaticBlockDefinition Record {[[BodyFunction]]:bodyFunction }.
15.7.12 Runtime Semantics: EvaluateClassStaticBlockBody
The
Assert :functionObject is a synthetic function created byClassStaticBlockDefinitionEvaluation step5 .- Perform !
FunctionDeclarationInstantiation (functionObject, « »). - Return ?
Evaluation ofClassStaticBlockStatementList .
15.7.13 Runtime Semantics: ClassElementEvaluation
The
- Return ?
ClassFieldDefinitionEvaluation ofFieldDefinition with argumentobject.
- Return ?
MethodDefinitionEvaluation ofMethodDefinition with argumentsobject andfalse .
- Return
ClassStaticBlockDefinitionEvaluation ofClassStaticBlock with argumentobject.
- Return
unused .
15.7.14 Runtime Semantics: ClassDefinitionEvaluation
The
For ease of specification, private methods and accessors are included alongside private fields in the[[PrivateElements]] slot of class instances. However, any given object has either all or none of the private methods and accessors defined by a given class. This feature has been designed so that implementations may choose to implement private methods and accessors using a strategy which does not require tracking each method or accessor individually.
For example, an implementation could directly associate instance private methods with their correspondingthis value. Looking up an instance private method on an object then consists of checking that the class
This differs from private fields: because field initializers can throw during class instantiation, an individual object may have some proper subset of the private fields of a given class, and so private fields must in general be tracked individually.
It is defined piecewise over the following productions:
- Letenv be the LexicalEnvironment of the
running execution context . - LetclassEnv be
NewDeclarativeEnvironment (env). - IfclassBinding is not
undefined , then- Perform ! classEnv.CreateImmutableBinding(classBinding,
true ).
- Perform ! classEnv.CreateImmutableBinding(classBinding,
- LetouterPrivateEnvironment be the
running execution context 's PrivateEnvironment. - LetclassPrivateEnvironment be
NewPrivateEnvironment (outerPrivateEnvironment). - If
ClassBody is present, then- For each Stringdn of the
PrivateBoundIdentifiers ofClassBody , do- IfclassPrivateEnvironment.[[Names]] contains a
Private Name pn such thatpn.[[Description]] isdn, thenAssert : This is only possible for getter/setter pairs.
- Else,
- Letname be a new
Private Name whose[[Description]] isdn. - Appendname toclassPrivateEnvironment.[[Names]].
- Letname be a new
- IfclassPrivateEnvironment.[[Names]] contains a
- For each Stringdn of the
- If
ClassHeritage is not present, then- LetprotoParent be
%Object.prototype% . - LetconstructorParent be
%Function.prototype% .
- LetprotoParent be
- Else,
- Set the
running execution context 's LexicalEnvironment toclassEnv. - NOTE: The
running execution context 's PrivateEnvironment isouterPrivateEnvironment when evaluatingClassHeritage . - LetsuperclassRef be
Completion (Evaluation ofClassHeritage ). - Set the
running execution context 's LexicalEnvironment toenv. - Letsuperclass be ?
GetValue (?superclassRef). - Ifsuperclass is
null , then- LetprotoParent be
null . - LetconstructorParent be
%Function.prototype% .
- LetprotoParent be
- Else if
IsConstructor (superclass) isfalse , then- Throw a
TypeError exception.
- Throw a
- Else,
- LetprotoParent be ?
Get (superclass,"prototype" ). - IfprotoParent
is not an Object andprotoParent is notnull , throw aTypeError exception. - LetconstructorParent besuperclass.
- LetprotoParent be ?
- Set the
- Letproto be
OrdinaryObjectCreate (protoParent). - If
ClassBody is not present, letconstructor beempty . - Else, letconstructor be
ConstructorMethod ofClassBody . - Set the
running execution context 's LexicalEnvironment toclassEnv. - Set the
running execution context 's PrivateEnvironment toclassPrivateEnvironment. - Ifconstructor is
empty , then- LetdefaultConstructor be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- Letargs be the
List of arguments that was passed to this function by[[Call]] or[[Construct]]. - If NewTarget is
undefined , throw aTypeError exception. - LetF be the
active function object . - IfF.[[ConstructorKind]] is
derived , then- NOTE: This branch behaves similarly to
constructor(...args) { super(...args); }. The most notable distinction is that while the aforementionedECMAScript source text observably calls the@@iterator method on%Array.prototype%, this function does not. - Letfunc be ! F.[[GetPrototypeOf]]().
- If
IsConstructor (func) isfalse , throw aTypeError exception. - Letresult be ?
Construct (func,args, NewTarget).
- NOTE: This branch behaves similarly to
- Else,
- NOTE: This branch behaves similarly to
constructor() {}. - Letresult be ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- NOTE: This branch behaves similarly to
- Perform ?
InitializeInstanceElements (result,F). - Returnresult.
- Letargs be the
- LetF be
CreateBuiltinFunction (defaultConstructor, 0,className, «[[ConstructorKind]],[[SourceText]] »,the current Realm Record ,constructorParent).
- LetdefaultConstructor be a new
- Else,
- LetconstructorInfo be !
DefineMethod ofconstructor with argumentsproto andconstructorParent. - LetF beconstructorInfo.[[Closure]].
- Perform
MakeClassConstructor (F). - Perform
SetFunctionName (F,className).
- LetconstructorInfo be !
- Perform
MakeConstructor (F,false ,proto). - If
ClassHeritage is present, setF.[[ConstructorKind]] toderived . - Perform !
DefineMethodProperty (proto,"constructor" ,F,false ). - If
ClassBody is not present, letelements be a new emptyList . - Else, letelements be
NonConstructorElements ofClassBody . - LetinstancePrivateMethods be a new empty
List . - LetstaticPrivateMethods be a new empty
List . - LetinstanceFields be a new empty
List . - LetstaticElements be a new empty
List . - For each
ClassElement e ofelements, do- If
IsStatic ofe isfalse , then- Letelement be
Completion (ClassElementEvaluation ofe with argumentproto).
- Letelement be
- Else,
- Letelement be
Completion (ClassElementEvaluation ofe with argumentF).
- Letelement be
- Ifelement is an
abrupt completion , then- Set the
running execution context 's LexicalEnvironment toenv. - Set the
running execution context 's PrivateEnvironment toouterPrivateEnvironment. - Return ? element.
- Set the
- Setelement to ! element.
- Ifelement is a
PrivateElement , thenAssert :element.[[Kind]] is eithermethod oraccessor .- If
IsStatic ofe isfalse , letcontainer beinstancePrivateMethods. - Else, letcontainer bestaticPrivateMethods.
- Ifcontainer contains a
PrivateElement pe such thatpe.[[Key]] iselement.[[Key]], thenAssert :element.[[Kind]] andpe.[[Kind]] are bothaccessor .- Ifelement.[[Get]] is
undefined , then- Letcombined be
PrivateElement {[[Key]]:element.[[Key]],[[Kind]]:accessor ,[[Get]]:pe.[[Get]],[[Set]]:element.[[Set]] }.
- Letcombined be
- Else,
- Letcombined be
PrivateElement {[[Key]]:element.[[Key]],[[Kind]]:accessor ,[[Get]]:element.[[Get]],[[Set]]:pe.[[Set]] }.
- Letcombined be
- Replacepe incontainer withcombined.
- Else,
- Appendelement tocontainer.
- Else ifelement is a
ClassFieldDefinition Record , then- If
IsStatic ofe isfalse , appendelement toinstanceFields. - Else, appendelement tostaticElements.
- If
- Else ifelement is a
ClassStaticBlockDefinition Record , then- Appendelement tostaticElements.
- If
- Set the
running execution context 's LexicalEnvironment toenv. - IfclassBinding is not
undefined , then- Perform ! classEnv.InitializeBinding(classBinding,F).
- SetF.[[PrivateMethods]] toinstancePrivateMethods.
- SetF.[[Fields]] toinstanceFields.
- For each
PrivateElement method ofstaticPrivateMethods, do- Perform !
PrivateMethodOrAccessorAdd (F,method).
- Perform !
- For each elementelementRecord ofstaticElements, do
- IfelementRecord is a
ClassFieldDefinition Record , then- Letresult be
Completion (DefineField (F,elementRecord)).
- Letresult be
- Else,
Assert :elementRecord is aClassStaticBlockDefinition Record .- Letresult be
Completion (Call (elementRecord.[[BodyFunction]],F)).
- Ifresult is an
abrupt completion , then- Set the
running execution context 's PrivateEnvironment toouterPrivateEnvironment. - Return ? result.
- Set the
- IfelementRecord is a
- Set the
running execution context 's PrivateEnvironment toouterPrivateEnvironment. - ReturnF.
15.7.15 Runtime Semantics: BindingClassDeclarationEvaluation
The
- LetclassName be
StringValue ofBindingIdentifier . - Letvalue be ?
ClassDefinitionEvaluation ofClassTail with argumentsclassName andclassName. - Setvalue.[[SourceText]] to the
source text matched by ClassDeclaration . - Letenv be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName (className,value,env). - Returnvalue.
- Letvalue be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"default" . - Setvalue.[[SourceText]] to the
source text matched by ClassDeclaration . - Returnvalue.
15.7.16 Runtime Semantics: Evaluation
- Perform ?
BindingClassDeclarationEvaluation of thisClassDeclaration . - Return
empty .
- Letvalue be ?
ClassDefinitionEvaluation ofClassTail with argumentsundefined and"" . - Setvalue.[[SourceText]] to the
source text matched by ClassExpression . - Returnvalue.
- LetclassName be
StringValue ofBindingIdentifier . - Letvalue be ?
ClassDefinitionEvaluation ofClassTail with argumentsclassName andclassName. - Setvalue.[[SourceText]] to the
source text matched by ClassExpression . - Returnvalue.
- LetprivateIdentifier be
StringValue ofPrivateIdentifier . - LetprivateEnvRec be the
running execution context 's PrivateEnvironment. - Letnames beprivateEnvRec.[[Names]].
Assert : Exactly one element ofnames is aPrivate Name whose[[Description]] isprivateIdentifier.- LetprivateName be the
Private Name innames whose[[Description]] isprivateIdentifier. - ReturnprivateName.
- Return
undefined .
15.8 Async Function Definitions
Syntax
await is parsed as a
- In an
AsyncFunctionBody . - In the
FormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression .AwaitExpression in this position is a Syntax error viastatic semantics . - In a
Module .
Whenawait may be parsed as an identifier when the[Await] parameter is absent. This includes the following contexts:
- Anywhere outside of an
AsyncFunctionBody orFormalParameters of anAsyncFunctionDeclaration ,AsyncFunctionExpression ,AsyncGeneratorDeclaration , orAsyncGeneratorExpression . - In the
BindingIdentifier of aFunctionExpression ,GeneratorExpression , orAsyncGeneratorExpression .
Unlike
15.8.1 Static Semantics: Early Errors
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofUniqueFormalParameters isfalse . - It is a Syntax Error if
HasDirectSuper ofAsyncMethod istrue . - It is a Syntax Error if
UniqueFormalParameters Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofUniqueFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody .
- It is a Syntax Error if
FunctionBodyContainsUseStrict ofAsyncFunctionBody istrue andIsSimpleParameterList ofFormalParameters isfalse . - It is a Syntax Error if
FormalParameters Contains AwaitExpression istrue . - If the
source text matched by FormalParameters isstrict mode code , the Early Error rules forUniqueFormalParameters : FormalParameters - If
BindingIdentifier is present and thesource text matched by BindingIdentifier isstrict mode code , it is a Syntax Error if theStringValue ofBindingIdentifier is either"eval" or"arguments" . - It is a Syntax Error if any element of the
BoundNames ofFormalParameters also occurs in theLexicallyDeclaredNames ofAsyncFunctionBody . - It is a Syntax Error if
FormalParameters Contains SuperProperty istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperProperty istrue . - It is a Syntax Error if
FormalParameters Contains SuperCall istrue . - It is a Syntax Error if
AsyncFunctionBody Contains SuperCall istrue .
15.8.2 Runtime Semantics: InstantiateAsyncFunctionObject
The
- Letname be
StringValue ofBindingIdentifier . - LetsourceText be the
source text matched by AsyncFunctionDeclaration . - LetF be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,name). - ReturnF.
- LetsourceText be the
source text matched by AsyncFunctionDeclaration . - LetF be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,"default" ). - ReturnF.
15.8.3 Runtime Semantics: InstantiateAsyncFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncFunctionExpression . - Letclosure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Returnclosure.
Assert :name is not present.- Setname to
StringValue ofBindingIdentifier . - LetouterEnv be the LexicalEnvironment of the
running execution context . - LetfuncEnv be
NewDeclarativeEnvironment (outerEnv). - Perform ! funcEnv.CreateImmutableBinding(name,
false ). - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncFunctionExpression . - Letclosure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,FormalParameters ,AsyncFunctionBody ,non-lexical-this ,funcEnv,privateEnv). - Perform
SetFunctionName (closure,name). - Perform ! funcEnv.InitializeBinding(name,closure).
- Returnclosure.
The
15.8.4 Runtime Semantics: EvaluateAsyncFunctionBody
The
- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetdeclResult be
Completion (FunctionDeclarationInstantiation (functionObject,argumentsList)). - IfdeclResult is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «declResult.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,FunctionBody ).
- Perform
- Return
Completion Record {[[Type]]:return ,[[Value]]:promiseCapability.[[Promise]],[[Target]]:empty }.
15.8.5 Runtime Semantics: Evaluation
- LetexprRef be ?
Evaluation ofUnaryExpression . - Letvalue be ?
GetValue (exprRef). - Return ?
Await (value).
15.9 Async Arrow Function Definitions
Syntax
Supplemental Syntax
When processing an instance of the production
the interpretation of
15.9.1 Static Semantics: Early Errors
- It is a Syntax Error if any element of the
BoundNames ofAsyncArrowBindingIdentifier also occurs in theLexicallyDeclaredNames ofAsyncConciseBody .
CoverCallExpressionAndAsyncArrowHead must cover anAsyncArrowHead .- It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains YieldExpression istrue . - It is a Syntax Error if
CoverCallExpressionAndAsyncArrowHead Contains AwaitExpression istrue . - It is a Syntax Error if any element of the
BoundNames ofCoverCallExpressionAndAsyncArrowHead also occurs in theLexicallyDeclaredNames ofAsyncConciseBody . - It is a Syntax Error if
AsyncConciseBodyContainsUseStrict ofAsyncConciseBody istrue andIsSimpleParameterList ofCoverCallExpressionAndAsyncArrowHead isfalse .
15.9.2 Static Semantics: AsyncConciseBodyContainsUseStrict
The
- Return
false .
15.9.3 Runtime Semantics: EvaluateAsyncConciseBody
The
- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetdeclResult be
Completion (FunctionDeclarationInstantiation (functionObject,argumentsList)). - IfdeclResult is an
abrupt completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «declResult.[[Value]] »).
- Perform !
- Else,
- Perform
AsyncFunctionStart (promiseCapability,ExpressionBody ).
- Perform
- Return
Completion Record {[[Type]]:return ,[[Value]]:promiseCapability.[[Promise]],[[Target]]:empty }.
15.9.4 Runtime Semantics: InstantiateAsyncArrowFunctionExpression
The
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncArrowFunction . - Letparameters be
AsyncArrowBindingIdentifier . - Letclosure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,parameters,AsyncConciseBody ,lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Returnclosure.
- Ifname is not present, setname to
"" . - Letenv be the LexicalEnvironment of the
running execution context . - LetprivateEnv be the
running execution context 's PrivateEnvironment. - LetsourceText be the
source text matched by AsyncArrowFunction . - Lethead be the
AsyncArrowHead that iscovered byCoverCallExpressionAndAsyncArrowHead . - Letparameters be the
ArrowFormalParameters ofhead. - Letclosure be
OrdinaryFunctionCreate (%AsyncFunction.prototype% ,sourceText,parameters,AsyncConciseBody ,lexical-this ,env,privateEnv). - Perform
SetFunctionName (closure,name). - Returnclosure.
15.9.5 Runtime Semantics: Evaluation
15.10 Tail Position Calls
15.10.1 Static Semantics: IsInTailPosition (call )
The abstract operation IsInTailPosition takes argumentcall (a
- If the
source text matched by call isnon-strict code , returnfalse . - Ifcall is not contained within a
FunctionBody , aConciseBody , or anAsyncConciseBody , returnfalse . - Letbody be the
FunctionBody ,ConciseBody , orAsyncConciseBody that most closely containscall. - Ifbody is the
FunctionBody of aGeneratorBody , returnfalse . - Ifbody is the
FunctionBody of anAsyncFunctionBody , returnfalse . - Ifbody is the
FunctionBody of anAsyncGeneratorBody , returnfalse . - Ifbody is an
AsyncConciseBody , returnfalse . - Return the result of
HasCallInTailPosition ofbody with argumentcall.
Tail Position calls are only defined in
15.10.2 Static Semantics: HasCallInTailPosition
The
call is a
A potential tail position call that is immediately followed by return
It is defined piecewise over the following productions:
- Lethas be
HasCallInTailPosition ofStatementList with argumentcall. - Ifhas is
true , returntrue . - Return
HasCallInTailPosition ofStatementListItem with argumentcall.
- Return
false .
- Lethas be
HasCallInTailPosition of the firstStatement with argumentcall. - Ifhas is
true , returntrue . - Return
HasCallInTailPosition of the secondStatement with argumentcall.
- Return
HasCallInTailPosition ofStatement with argumentcall.
- Return
HasCallInTailPosition ofLabelledItem with argumentcall.
- Return
HasCallInTailPosition ofExpression with argumentcall.
- Return
HasCallInTailPosition ofCaseBlock with argumentcall.
- Lethas be
false . - If the first
CaseClauses is present, sethas toHasCallInTailPosition of the firstCaseClauses with argumentcall. - Ifhas is
true , returntrue . - Sethas to
HasCallInTailPosition ofDefaultClause with argumentcall. - Ifhas is
true , returntrue . - If the second
CaseClauses is present, sethas toHasCallInTailPosition of the secondCaseClauses with argumentcall. - Returnhas.
- Lethas be
HasCallInTailPosition ofCaseClauses with argumentcall. - Ifhas is
true , returntrue . - Return
HasCallInTailPosition ofCaseClause with argumentcall.
- If
StatementList is present, returnHasCallInTailPosition ofStatementList with argumentcall. - Return
false .
- Return
HasCallInTailPosition ofCatch with argumentcall.
- Return
HasCallInTailPosition ofFinally with argumentcall.
- Return
HasCallInTailPosition ofBlock with argumentcall.
- Return
false .
- Return
HasCallInTailPosition ofAssignmentExpression with argumentcall.
- Lethas be
HasCallInTailPosition of the firstAssignmentExpression with argumentcall. - Ifhas is
true , returntrue . - Return
HasCallInTailPosition of the secondAssignmentExpression with argumentcall.
- Return
HasCallInTailPosition ofBitwiseORExpression with argumentcall.
- Return
HasCallInTailPosition ofLogicalANDExpression with argumentcall.
- Return
HasCallInTailPosition ofBitwiseORExpression with argumentcall.
- If this
CallExpression iscall, returntrue . - Return
false .
- Return
HasCallInTailPosition ofOptionalChain with argumentcall.
- Return
false .
- If this
OptionalChain iscall, returntrue . - Return
false .
- If this
MemberExpression iscall, returntrue . - Return
false .
- Letexpr be the
ParenthesizedExpression that iscovered byCoverParenthesizedExpressionAndArrowParameterList . - Return
HasCallInTailPosition ofexpr with argumentcall.
- Return
HasCallInTailPosition ofExpression with argumentcall.
15.10.3 PrepareForTailCall ( )
The abstract operation PrepareForTailCall takes no arguments and returns
Assert : The currentexecution context will not subsequently be used for the evaluation of any ECMAScript code or built-in functions. The invocation of Call subsequent to the invocation of this abstract operation will create and push a newexecution context before performing any such evaluation.- Discard all resources associated with the current
execution context . - Return
unused .
A tail position call must either release any transient internal resources associated with the currently executing function
For example, a tail position call should only grow an implementation's activation record stack by the amount that the size of the target function's activation record exceeds the size of the calling function's activation record. If the target function's activation record is smaller, then the total size of the stack should decrease.
16 ECMAScript Language: Scripts and Modules
16.1 Scripts
Syntax
16.1.1 Static Semantics: Early Errors
- It is a Syntax Error if the
LexicallyDeclaredNames ofScriptBody contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofScriptBody also occurs in theVarDeclaredNames ofScriptBody .
- It is a Syntax Error if
StatementList Contains superunless the source text containingsuperis eval code that is being processed by adirect eval . Additionalearly error rules forsuperwithindirect eval are defined in19.2.1.1 . - It is a Syntax Error if
StatementList Contains NewTarget unless the source text containingNewTarget is eval code that is being processed by adirect eval . Additionalearly error rules forNewTarget indirect eval are defined in19.2.1.1 . - It is a Syntax Error if
ContainsDuplicateLabels ofStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedBreakTarget ofStatementList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedContinueTarget ofStatementList with arguments « » and « » istrue . - It is a Syntax Error if
AllPrivateIdentifiersValid ofStatementList with argument « » isfalse unless the source text containingScriptBody is eval code that is being processed by adirect eval .
16.1.2 Static Semantics: IsStrict
The
- If
ScriptBody is present and theDirective Prologue ofScriptBody contains aUse Strict Directive , returntrue ; otherwise, returnfalse .
16.1.3 Runtime Semantics: Evaluation
- Return
undefined .
16.1.4 Script Records
AScript Record encapsulates information about a script being evaluated. Each script record contains the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] | a | The |
| [[ECMAScriptCode]] | a | The result of parsing the source text of this script. |
| [[LoadedModules]] | a | A map from the specifier strings imported by this script to the resolved |
| [[HostDefined]] | anything (default value is | Field reserved for use by |
16.1.5 ParseScript (sourceText,realm,hostDefined )
The abstract operation ParseScript takes argumentssourceText (
- Letscript be
ParseText (sourceText,Script ). - Ifscript is a
List of errors, returnscript. - Return
Script Record {[[Realm]]:realm,[[ECMAScriptCode]]:script,[[LoadedModules]]: « »,[[HostDefined]]:hostDefined }.
An implementation may parse script source text and analyse it for Early Error conditions prior to evaluation of ParseScript for that script source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseScript upon that source text.
16.1.6 ScriptEvaluation (scriptRecord )
The abstract operation ScriptEvaluation takes argumentscriptRecord (a
- LetglobalEnv bescriptRecord.[[Realm]].[[GlobalEnv]].
- LetscriptContext be a new
ECMAScript code execution context . - Set the Function ofscriptContext to
null . - Set the
Realm ofscriptContext toscriptRecord.[[Realm]]. - Set the ScriptOrModule ofscriptContext toscriptRecord.
- Set the VariableEnvironment ofscriptContext toglobalEnv.
- Set the LexicalEnvironment ofscriptContext toglobalEnv.
- Set the PrivateEnvironment ofscriptContext to
null . - Suspend the
running execution context . - PushscriptContext onto the
execution context stack ;scriptContext is now therunning execution context . - Letscript bescriptRecord.[[ECMAScriptCode]].
- Letresult be
Completion (GlobalDeclarationInstantiation (script,globalEnv)). - Ifresult is a
normal completion , then- Setresult to
Completion (Evaluation ofscript). - Ifresult is a
normal completion andresult.[[Value]] isempty , then- Setresult to
NormalCompletion (undefined ).
- Setresult to
- Setresult to
- SuspendscriptContext and remove it from the
execution context stack . Assert : Theexecution context stack is not empty.- Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
16.1.7 GlobalDeclarationInstantiation (script,env )
The abstract operation GlobalDeclarationInstantiation takes argumentsscript (a
When an
It performs the following steps when called:
- LetlexNames be the
LexicallyDeclaredNames ofscript. - LetvarNames be the
VarDeclaredNames ofscript. - For each elementname oflexNames, do
- Ifenv.HasVarDeclaration(name) is
true , throw aSyntaxError exception. - Ifenv.HasLexicalDeclaration(name) is
true , throw aSyntaxError exception. - LethasRestrictedGlobal be ? env.HasRestrictedGlobalProperty(name).
- IfhasRestrictedGlobal is
true , throw aSyntaxError exception.
- Ifenv.HasVarDeclaration(name) is
- For each elementname ofvarNames, do
- Ifenv.HasLexicalDeclaration(name) is
true , throw aSyntaxError exception.
- Ifenv.HasLexicalDeclaration(name) is
- LetvarDeclarations be the
VarScopedDeclarations ofscript. - LetfunctionsToInitialize be a new empty
List . - LetdeclaredFunctionNames be a new empty
List . - For each elementd ofvarDeclarations, in reverse
List order, do- Ifd is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert :d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Letfn be the sole element of the
BoundNames ofd. - IfdeclaredFunctionNames does not containfn, then
- LetfnDefinable be ? env.CanDeclareGlobalFunction(fn).
- IffnDefinable is
false , throw aTypeError exception. - Appendfn todeclaredFunctionNames.
- Insertd as the first element offunctionsToInitialize.
- Ifd is not either a
- LetdeclaredVarNames be a new empty
List . - For each elementd ofvarDeclarations, do
- Ifd is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each Stringvn of the
BoundNames ofd, do- IfdeclaredFunctionNames does not containvn, then
- LetvnDefinable be ? env.CanDeclareGlobalVar(vn).
- IfvnDefinable is
false , throw aTypeError exception. - IfdeclaredVarNames does not containvn, then
- Appendvn todeclaredVarNames.
- IfdeclaredFunctionNames does not containvn, then
- For each Stringvn of the
- Ifd is either a
- NOTE: No abnormal terminations occur after this algorithm step if the
global object is anordinary object . However, if theglobal object is aProxy exotic object it may exhibit behaviours that cause abnormal terminations in some of the following steps. - NOTE: Annex
B.3.2.2 adds additional steps at this point. - LetlexDeclarations be the
LexicallyScopedDeclarations ofscript. - LetprivateEnv be
null . - For each elementd oflexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each elementdn of the
BoundNames ofd, do- If
IsConstantDeclaration ofd istrue , then- Perform ? env.CreateImmutableBinding(dn,
true ).
- Perform ? env.CreateImmutableBinding(dn,
- Else,
- Perform ? env.CreateMutableBinding(dn,
false ).
- Perform ? env.CreateMutableBinding(dn,
- If
- For each
Parse Node f offunctionsToInitialize, do- Letfn be the sole element of the
BoundNames off. - Letfo be
InstantiateFunctionObject off with argumentsenv andprivateEnv. - Perform ? env.CreateGlobalFunctionBinding(fn,fo,
false ).
- Letfn be the sole element of the
- For each Stringvn ofdeclaredVarNames, do
- Perform ? env.CreateGlobalVarBinding(vn,
false ).
- Perform ? env.CreateGlobalVarBinding(vn,
- Return
unused .
Unlike explicit var or function declarations, properties that are directly created on the
16.2 Modules
Syntax
16.2.1 Module Semantics
16.2.1.1 Static Semantics: Early Errors
- It is a Syntax Error if the
LexicallyDeclaredNames ofModuleItemList contains any duplicate entries. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofModuleItemList also occurs in theVarDeclaredNames ofModuleItemList . - It is a Syntax Error if the
ExportedNames ofModuleItemList contains any duplicate entries. - It is a Syntax Error if any element of the
ExportedBindings ofModuleItemList does not also occur in either theVarDeclaredNames ofModuleItemList , or theLexicallyDeclaredNames ofModuleItemList . - It is a Syntax Error if
ModuleItemList Contains super. - It is a Syntax Error if
ModuleItemList Contains NewTarget . - It is a Syntax Error if
ContainsDuplicateLabels ofModuleItemList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedBreakTarget ofModuleItemList with argument « » istrue . - It is a Syntax Error if
ContainsUndefinedContinueTarget ofModuleItemList with arguments « » and « » istrue . - It is a Syntax Error if
AllPrivateIdentifiersValid ofModuleItemList with argument « » isfalse .
The duplicateexport default
- It is a Syntax Error if
IsStringWellFormedUnicode (theSV ofStringLiteral ) isfalse .
16.2.1.2 Static Semantics: ImportedLocalNames (importEntries )
The abstract operation ImportedLocalNames takes argumentimportEntries (a
- LetlocalNames be a new empty
List . - For each
ImportEntry Record i ofimportEntries, do- Appendi.[[LocalName]] tolocalNames.
- ReturnlocalNames.
16.2.1.3 Static Semantics: ModuleRequests
The
- Return a new empty
List .
- Return
ModuleRequests ofModuleItem .
- LetmoduleNames be
ModuleRequests ofModuleItemList . - LetadditionalNames be
ModuleRequests ofModuleItem . - For each Stringname ofadditionalNames, do
- IfmoduleNames does not containname, then
- Appendname tomoduleNames.
- IfmoduleNames does not containname, then
- ReturnmoduleNames.
- Return a new empty
List .
- Return
ModuleRequests ofFromClause .
- Return a
List whose sole element is theSV ofStringLiteral .
- Return the
ModuleRequests ofFromClause .
- Return a new empty
List .
16.2.1.4 Abstract Module Records
AModule Record encapsulates structural information about the imports and exports of a single module. This information is used to link the imports and exports of sets of connected modules. A Module Record includes four fields that are only used when evaluating a module.
For specification purposes Module Record values are values of the
Module Record defines the fields listed in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Realm]] | a | The |
| [[Environment]] | a | The |
| [[Namespace]] | an Object or | The Module Namespace Object ( |
| [[HostDefined]] | anything (default value is | Field reserved for use by |
| Method | Purpose |
|---|---|
| LoadRequestedModules( [hostDefined ] ) | Prepares the module for linking by recursively loading all its dependencies, and returns a promise. |
| GetExportedNames([exportStarSet]) | Return a list of all names that are either directly or indirectly exported from this module. LoadRequestedModules must have completed successfully prior to invoking this method. |
| ResolveExport(exportName [,resolveSet]) | Return the binding of a name exported by this module. Bindings are represented by aResolvedBinding Record, of the form {[[Module]]: Each time this operation is called with a specificexportName,resolveSet pair as arguments it must return the same result. LoadRequestedModules must have completed successfully prior to invoking this method. |
| Link() | Prepare the module for evaluation by transitively resolving all module dependencies and creating a LoadRequestedModules must have completed successfully prior to invoking this method. |
| Evaluate() | Returns a promise for the evaluation of this module and its dependencies, resolving on successful evaluation or if it has already been evaluated successfully, and rejecting for an evaluation error or if it has already been evaluated unsuccessfully. If the promise is rejected, Link must have completed successfully prior to invoking this method. |
16.2.1.5 Cyclic Module Records
ACyclic Module Record is used to represent information about a module that can participate in dependency cycles with other modules that are subclasses of the
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[Status]] | Initially | |
| [[EvaluationError]] | a | A |
| [[DFSIndex]] | an | Auxiliary field used during Link and Evaluate only. If[[Status]] is either |
| [[DFSAncestorIndex]] | an | Auxiliary field used during Link and Evaluate only. If[[Status]] is either |
| [[RequestedModules]] | a | A |
| [[LoadedModules]] | a | A map from the specifier strings used by the module represented by this record to request the importation of a module to the resolved |
| [[CycleRoot]] | a | The first visited module of the cycle, the root DFS ancestor of the strongly connected component. For a module not in a cycle, this would be the module itself. Once Evaluate has completed, a module's[[DFSAncestorIndex]] is the[[DFSIndex]] of its[[CycleRoot]]. |
| [[HasTLA]] | a Boolean | Whether this module is individually asynchronous (for example, if it's a |
| [[AsyncEvaluation]] | a Boolean | Whether this module is either itself asynchronous or has an asynchronous dependency. Note: The order in which this field is set is used to order queued executions, see |
| [[TopLevelCapability]] | a | If this module is the[[CycleRoot]] of some cycle, and Evaluate() was called on some module in that cycle, this field contains the |
| [[AsyncParentModules]] | a | If this module or a dependency has[[HasTLA]] |
| [[PendingAsyncDependencies]] | an | If this module has any asynchronous dependencies, this tracks the number of asynchronous dependency modules remaining to execute for this module. A module with asynchronous dependencies will be executed when this field reaches 0 and there are no execution errors. |
In addition to the methods defined in
| Method | Purpose |
|---|---|
| InitializeEnvironment() | Initialize the |
| ExecuteModule( [promiseCapability ] ) | Evaluate the module's code within its |
AGraphLoadingState Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[PromiseCapability]] | a | The promise to resolve when the loading process finishes. |
| [[IsLoading]] | a Boolean | It is true if the loading process has not finished yet, neither successfully nor with an error. |
| [[PendingModulesCount]] | a non-negative | It tracks the number of pending |
| [[Visited]] | a | It is a list of the |
| [[HostDefined]] | anything (default value is | It contains |
16.2.1.5.1 LoadRequestedModules ( [hostDefined ] )
The LoadRequestedModules concrete method of a
- IfhostDefined is not present, lethostDefined be
empty . - Letpc be !
NewPromiseCapability (%Promise% ). - Letstate be the
GraphLoadingState Record {[[IsLoading]]:true ,[[PendingModulesCount]]: 1,[[Visited]]: « »,[[PromiseCapability]]:pc,[[HostDefined]]:hostDefined }. - Perform
InnerModuleLoading (state,module). - Returnpc.[[Promise]].
<link rel="preload" as="..."> tags.import() expressions never set thehostDefined parameter.16.2.1.5.1.1 InnerModuleLoading (state,module )
The abstract operation InnerModuleLoading takes argumentsstate (a
Assert :state.[[IsLoading]] istrue .- Ifmodule is a
Cyclic Module Record ,module.[[Status]] isnew , andstate.[[Visited]] does not containmodule, then- Appendmodule tostate.[[Visited]].
- LetrequestedModulesCount be the number of elements inmodule.[[RequestedModules]].
- Setstate.[[PendingModulesCount]] tostate.[[PendingModulesCount]] +requestedModulesCount.
- For each Stringrequired ofmodule.[[RequestedModules]], do
- Ifmodule.[[LoadedModules]] contains a
Record whose[[Specifier]] isrequired, then- Letrecord be that
Record . - Perform
InnerModuleLoading (state,record.[[Module]]).
- Letrecord be that
- Else,
- Perform
HostLoadImportedModule (module,required,state.[[HostDefined]],state). - NOTE:
HostLoadImportedModule will callFinishLoadingImportedModule , which re-enters the graph loading process throughContinueModuleLoading .
- Perform
- Ifstate.[[IsLoading]] is
false , returnunused .
- Ifmodule.[[LoadedModules]] contains a
Assert :state.[[PendingModulesCount]] ≥ 1.- Setstate.[[PendingModulesCount]] tostate.[[PendingModulesCount]] - 1.
- Ifstate.[[PendingModulesCount]] = 0, then
- Setstate.[[IsLoading]] to
false . - For each
Cyclic Module Record loaded ofstate.[[Visited]], do- Ifloaded.[[Status]] is
new , setloaded.[[Status]] tounlinked .
- Ifloaded.[[Status]] is
- Perform !
Call (state.[[PromiseCapability]].[[Resolve]],undefined , «undefined »).
- Setstate.[[IsLoading]] to
- Return
unused .
16.2.1.5.1.2 ContinueModuleLoading (state,moduleCompletion )
The abstract operation ContinueModuleLoading takes argumentsstate (a
- Ifstate.[[IsLoading]] is
false , returnunused . - IfmoduleCompletion is a
normal completion , then- Perform
InnerModuleLoading (state,moduleCompletion.[[Value]]).
- Perform
- Else,
- Setstate.[[IsLoading]] to
false . - Perform !
Call (state.[[PromiseCapability]].[[Reject]],undefined , «moduleCompletion.[[Value]] »).
- Setstate.[[IsLoading]] to
- Return
unused .
16.2.1.5.2 Link ( )
The Link concrete method of a
Assert :module.[[Status]] is one ofunlinked ,linked ,evaluating-async , orevaluated .- Letstack be a new empty
List . - Letresult be
Completion (InnerModuleLinking (module,stack, 0)). - Ifresult is an
abrupt completion , then- For each
Cyclic Module Record m ofstack, doAssert :m.[[Status]] islinking .- Setm.[[Status]] to
unlinked .
Assert :module.[[Status]] isunlinked .- Return ? result.
- For each
Assert :module.[[Status]] is one oflinked ,evaluating-async , orevaluated .Assert :stack is empty.- Return
unused .
16.2.1.5.2.1 InnerModuleLinking (module,stack,index )
The abstract operation InnerModuleLinking takes argumentsmodule (a
- Ifmodule is not a
Cyclic Module Record , then- Perform ? module.Link().
- Returnindex.
- Ifmodule.[[Status]] is one of
linking ,linked ,evaluating-async , orevaluated , then- Returnindex.
Assert :module.[[Status]] isunlinked .- Setmodule.[[Status]] to
linking . - Setmodule.[[DFSIndex]] toindex.
- Setmodule.[[DFSAncestorIndex]] toindex.
- Setindex toindex + 1.
- Appendmodule tostack.
- For each Stringrequired ofmodule.[[RequestedModules]], do
- LetrequiredModule be
GetImportedModule (module,required). - Setindex to ?
InnerModuleLinking (requiredModule,stack,index). - IfrequiredModule is a
Cyclic Module Record , thenAssert :requiredModule.[[Status]] is one oflinking ,linked ,evaluating-async , orevaluated .Assert :requiredModule.[[Status]] islinking if and only ifstack containsrequiredModule.- IfrequiredModule.[[Status]] is
linking , then- Setmodule.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]],requiredModule.[[DFSAncestorIndex]]).
- Setmodule.[[DFSAncestorIndex]] to
- LetrequiredModule be
- Perform ? module.InitializeEnvironment().
Assert :module occurs exactly once instack.Assert :module.[[DFSAncestorIndex]] ≤module.[[DFSIndex]].- Ifmodule.[[DFSAncestorIndex]] =module.[[DFSIndex]], then
- Letdone be
false . - Repeat, whiledone is
false ,- LetrequiredModule be the last element ofstack.
- Remove the last element ofstack.
Assert :requiredModule is aCyclic Module Record .- SetrequiredModule.[[Status]] to
linked . - IfrequiredModule andmodule are the same
Module Record , setdone totrue .
- Letdone be
- Returnindex.
16.2.1.5.3 Evaluate ( )
The Evaluate concrete method of a
Assert : This call to Evaluate is not happening at the same time as another call to Evaluate within thesurrounding agent .Assert :module.[[Status]] is one oflinked ,evaluating-async , orevaluated .- Ifmodule.[[Status]] is either
evaluating-async orevaluated , setmodule tomodule.[[CycleRoot]]. - Ifmodule.[[TopLevelCapability]] is not
empty , then- Returnmodule.[[TopLevelCapability]].[[Promise]].
- Letstack be a new empty
List . - Letcapability be !
NewPromiseCapability (%Promise% ). - Setmodule.[[TopLevelCapability]] tocapability.
- Letresult be
Completion (InnerModuleEvaluation (module,stack, 0)). - Ifresult is an
abrupt completion , then- For each
Cyclic Module Record m ofstack, doAssert :m.[[Status]] isevaluating .- Setm.[[Status]] to
evaluated . - Setm.[[EvaluationError]] toresult.
Assert :module.[[Status]] isevaluated .Assert :module.[[EvaluationError]] isresult.- Perform !
Call (capability.[[Reject]],undefined , «result.[[Value]] »).
- For each
- Else,
- Returncapability.[[Promise]].
16.2.1.5.3.1 InnerModuleEvaluation (module,stack,index )
The abstract operation InnerModuleEvaluation takes argumentsmodule (a
- Ifmodule is not a
Cyclic Module Record , then- Letpromise be ! module.Evaluate().
Assert :promise.[[PromiseState]] is notpending .- Ifpromise.[[PromiseState]] is
rejected , then- Return
ThrowCompletion (promise.[[PromiseResult]]).
- Return
- Returnindex.
- Ifmodule.[[Status]] is either
evaluating-async orevaluated , then- Ifmodule.[[EvaluationError]] is
empty , returnindex. - Otherwise, return ? module.[[EvaluationError]].
- Ifmodule.[[EvaluationError]] is
- Ifmodule.[[Status]] is
evaluating , returnindex. Assert :module.[[Status]] islinked .- Setmodule.[[Status]] to
evaluating . - Setmodule.[[DFSIndex]] toindex.
- Setmodule.[[DFSAncestorIndex]] toindex.
- Setmodule.[[PendingAsyncDependencies]] to 0.
- Setindex toindex + 1.
- Appendmodule tostack.
- For each Stringrequired ofmodule.[[RequestedModules]], do
- LetrequiredModule be
GetImportedModule (module,required). - Setindex to ?
InnerModuleEvaluation (requiredModule,stack,index). - IfrequiredModule is a
Cyclic Module Record , thenAssert :requiredModule.[[Status]] is one ofevaluating ,evaluating-async , orevaluated .Assert :requiredModule.[[Status]] isevaluating if and only ifstack containsrequiredModule.- IfrequiredModule.[[Status]] is
evaluating , then- Setmodule.[[DFSAncestorIndex]] to
min (module.[[DFSAncestorIndex]],requiredModule.[[DFSAncestorIndex]]).
- Setmodule.[[DFSAncestorIndex]] to
- Else,
- SetrequiredModule torequiredModule.[[CycleRoot]].
Assert :requiredModule.[[Status]] is eitherevaluating-async orevaluated .- IfrequiredModule.[[EvaluationError]] is not
empty , return ? requiredModule.[[EvaluationError]].
- IfrequiredModule.[[AsyncEvaluation]] is
true , then- Setmodule.[[PendingAsyncDependencies]] tomodule.[[PendingAsyncDependencies]] + 1.
- Appendmodule torequiredModule.[[AsyncParentModules]].
- LetrequiredModule be
- Ifmodule.[[PendingAsyncDependencies]] > 0 ormodule.[[HasTLA]] is
true , thenAssert :module.[[AsyncEvaluation]] isfalse and was never previously set totrue .- Setmodule.[[AsyncEvaluation]] to
true . - NOTE: The order in which module records have their[[AsyncEvaluation]] fields transition to
true is significant. (See16.2.1.5.3.4 .) - Ifmodule.[[PendingAsyncDependencies]] = 0, perform
ExecuteAsyncModule (module).
- Else,
- Perform ? module.ExecuteModule().
Assert :module occurs exactly once instack.Assert :module.[[DFSAncestorIndex]] ≤module.[[DFSIndex]].- Ifmodule.[[DFSAncestorIndex]] =module.[[DFSIndex]], then
- Letdone be
false . - Repeat, whiledone is
false ,- LetrequiredModule be the last element ofstack.
- Remove the last element ofstack.
Assert :requiredModule is aCyclic Module Record .- IfrequiredModule.[[AsyncEvaluation]] is
false , setrequiredModule.[[Status]] toevaluated . - Otherwise, setrequiredModule.[[Status]] to
evaluating-async . - IfrequiredModule andmodule are the same
Module Record , setdone totrue . - SetrequiredModule.[[CycleRoot]] tomodule.
- Letdone be
- Returnindex.
A module is
Any modules depending on a module of an asynchronous cycle when that cycle is not
16.2.1.5.3.2 ExecuteAsyncModule (module )
The abstract operation ExecuteAsyncModule takes argumentmodule (a
Assert :module.[[Status]] is eitherevaluating orevaluating-async .Assert :module.[[HasTLA]] istrue .- Letcapability be !
NewPromiseCapability (%Promise% ). - LetfulfilledClosure be a new
Abstract Closure with no parameters that capturesmodule and performs the following steps when called:- Perform
AsyncModuleExecutionFulfilled (module). - Return
undefined .
- Perform
- LetonFulfilled be
CreateBuiltinFunction (fulfilledClosure, 0,"" , « »). - LetrejectedClosure be a new
Abstract Closure with parameters (error) that capturesmodule and performs the following steps when called:- Perform
AsyncModuleExecutionRejected (module,error). - Return
undefined .
- Perform
- LetonRejected be
CreateBuiltinFunction (rejectedClosure, 0,"" , « »). - Perform
PerformPromiseThen (capability.[[Promise]],onFulfilled,onRejected). - Perform ! module.ExecuteModule(capability).
- Return
unused .
16.2.1.5.3.3 GatherAvailableAncestors (module,execList )
The abstract operation GatherAvailableAncestors takes argumentsmodule (a
- For each
Cyclic Module Record m ofmodule.[[AsyncParentModules]], do- IfexecList does not containm andm.[[CycleRoot]].[[EvaluationError]] is
empty , thenAssert :m.[[Status]] isevaluating-async .Assert :m.[[EvaluationError]] isempty .Assert :m.[[AsyncEvaluation]] istrue .Assert :m.[[PendingAsyncDependencies]] > 0.- Setm.[[PendingAsyncDependencies]] tom.[[PendingAsyncDependencies]] - 1.
- Ifm.[[PendingAsyncDependencies]] = 0, then
- Appendm toexecList.
- Ifm.[[HasTLA]] is
false , performGatherAvailableAncestors (m,execList).
- IfexecList does not containm andm.[[CycleRoot]].[[EvaluationError]] is
- Return
unused .
When an asynchronous execution for a rootmodule is fulfilled, this function determines the list of modules which are able to synchronously execute together on this completion, populating them inexecList.
16.2.1.5.3.4 AsyncModuleExecutionFulfilled (module )
The abstract operation AsyncModuleExecutionFulfilled takes argumentmodule (a
- Ifmodule.[[Status]] is
evaluated , thenAssert :module.[[EvaluationError]] is notempty .- Return
unused .
Assert :module.[[Status]] isevaluating-async .Assert :module.[[AsyncEvaluation]] istrue .Assert :module.[[EvaluationError]] isempty .- Setmodule.[[AsyncEvaluation]] to
false . - Setmodule.[[Status]] to
evaluated . - Ifmodule.[[TopLevelCapability]] is not
empty , then - LetexecList be a new empty
List . - Perform
GatherAvailableAncestors (module,execList). - LetsortedExecList be a
List whose elements are the elements ofexecList, in the order in which they had their[[AsyncEvaluation]] fields set totrue inInnerModuleEvaluation . Assert : All elements ofsortedExecList have their[[AsyncEvaluation]] field set totrue ,[[PendingAsyncDependencies]] field set to 0, and[[EvaluationError]] field set toempty .- For each
Cyclic Module Record m ofsortedExecList, do- Ifm.[[Status]] is
evaluated , thenAssert :m.[[EvaluationError]] is notempty .
- Else ifm.[[HasTLA]] is
true , then- Perform
ExecuteAsyncModule (m).
- Perform
- Else,
- Letresult bem.ExecuteModule().
- Ifresult is an
abrupt completion , then- Perform
AsyncModuleExecutionRejected (m,result.[[Value]]).
- Perform
- Else,
- Ifm.[[Status]] is
- Return
unused .
16.2.1.5.3.5 AsyncModuleExecutionRejected (module,error )
The abstract operation AsyncModuleExecutionRejected takes argumentsmodule (a
- Ifmodule.[[Status]] is
evaluated , thenAssert :module.[[EvaluationError]] is notempty .- Return
unused .
Assert :module.[[Status]] isevaluating-async .Assert :module.[[AsyncEvaluation]] istrue .Assert :module.[[EvaluationError]] isempty .- Setmodule.[[EvaluationError]] to
ThrowCompletion (error). - Setmodule.[[Status]] to
evaluated . - For each
Cyclic Module Record m ofmodule.[[AsyncParentModules]], do- Perform
AsyncModuleExecutionRejected (m,error).
- Perform
- Ifmodule.[[TopLevelCapability]] is not
empty , then - Return
unused .
16.2.1.5.4 Example Cyclic Module Record Graphs
This non-normative section gives a series of examples of the linking and evaluation of a few common module graphs, with a specific focus on how errors can occur.
First consider the following simple module graph:
Let's first assume that there are no error conditions. When a
Consider then cases involving linking errors, after a successful call toA.LoadRequestedModules(). If
Finally, consider a case involving evaluation errors after a successful call to Link(). If
Now consider a different type of error condition:
In this scenario, moduleA declares a dependency on some other module, but no
The difference here between loading, linking and evaluation errors is due to the following characteristic:
Evaluation must be only performed once, as it can cause side effects; it is thus important to remember whether evaluation has already been performed, even if unsuccessfully. (In the error case, it makes sense to also remember the exception because otherwise subsequent Evaluate() calls would have to synthesize a new one.)- Linking, on the other hand, is side-effect-free, and thus even if it fails, it can be retried at a later time with no issues.
- Loading closely interacts with the
host , and it may be desiderable for some of them to allow users to retry failed loads (for example, if the failure is caused by temporarily bad network conditions).
Now, consider a module graph with a cycle:
Here we assume that the entry point is moduleA, so that the
Then the
An analogous story occurs for the evaluation phase of a cyclic module graph, in the success case.
Now consider a case whereA has a linking error; for example, it tries to import a binding fromC that does not exist. In that case, the above steps still occur, including the early return from the second call to
Alternatively, consider a case whereA has an evaluation error; for example, its source code throws an exception. In that case, the evaluation-time analog of the above steps still occurs, including the early return from the second call toawait through the whole dependency graph through the
Lastly, consider a module graph with a cycle, where all modules complete asynchronously:
Loading and linking happen as before, and all modules end up with[[Status]] set to
CallingA.Evaluate() calls
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 2 (B andC) | ||
| B | 1 | 0 | «A » | 1 (D) | ||
| C | 2 | 0 | «A » | 2 (D andE) | ||
| D | 3 | 0 | «B,C » | 0 | ||
| E | 4 | 4 | «C » | 0 |
Let us assume thatE finishes executing first. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| C | 2 | 0 | «A » | 1 (D) | ||
| E | 4 | 4 | «C » | 0 |
D is next to finish (as it was the only module that was still executing). When that happens,await). The fields of the updated modules are as given in
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| B | 1 | 0 | «A » | 0 | ||
| C | 2 | 0 | «A » | 0 | ||
| D | 3 | 0 | «B,C » | 0 |
Let us assume thatC finishes executing next. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 1 (B) | ||
| C | 2 | 0 | «A » | 0 |
Then,B finishes executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | ||
| B | 1 | 0 | «A » | 0 |
Finally,A finishes executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] |
|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 |
Alternatively, consider a failure case whereC fails execution and returns an error beforeB has finished executing. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 1 (B) | |||
| C | 2 | 1 | «A » | 0 | C's evaluation error |
A will be rejected with the same error asC sinceC will call
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | C's |
Then,B finishes executing without an error. When that happens,
| Module | [[DFSIndex]] | [[DFSAncestorIndex]] | [[Status]] | [[AsyncEvaluation]] | [[AsyncParentModules]] | [[PendingAsyncDependencies]] | [[EvaluationError]] |
|---|---|---|---|---|---|---|---|
| A | 0 | 0 | « » | 0 | C's | ||
| B | 1 | 0 | «A » | 0 |
16.2.1.6 Source Text Module Records
ASource Text Module Record is used to represent information about a module that was defined from
A
In addition to the fields defined in
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ECMAScriptCode]] | a | The result of parsing the source text of this module using |
| [[Context]] | an | The |
| [[ImportMeta]] | an Object or | An object exposed through theimport.meta meta property. It is |
| [[ImportEntries]] | a | A |
| [[LocalExportEntries]] | a | A |
| [[IndirectExportEntries]] | a | Aexport * as namespace declarations. |
| [[StarExportEntries]] | a | Aexport * declarations that occur within the module, not includingexport * as namespace declarations. |
AnImportEntry Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ModuleRequest]] | a String | String value of the |
| [[ImportName]] | a String or | The name under which the desired binding is exported by the module identified by[[ModuleRequest]]. The value |
| [[LocalName]] | a String | The name that is used to locally access the imported value from within the importing module. |
| Import Statement Form | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|
import v from "mod"; | |||
import * as ns from "mod"; | |||
import {x} from "mod"; | |||
import {x as v} from "mod"; | |||
import "mod"; | An | ||
AnExportEntry Record is a
| Field Name | Value Type | Meaning |
|---|---|---|
| [[ExportName]] | a String or | The name used to export this binding by this module. |
| [[ModuleRequest]] | a String or | The String value of the |
| [[ImportName]] | a String, | The name under which the desired binding is exported by the module identified by[[ModuleRequest]].export * as ns from "mod" declarations.export * from "mod" declarations. |
| [[LocalName]] | a String or | The name that is used to locally access the exported value from within the importing module. |
| Export Statement Form | [[ExportName]] | [[ModuleRequest]] | [[ImportName]] | [[LocalName]] |
|---|---|---|---|---|
export var v; | ||||
export default function f() {} | ||||
export default function () {} | ||||
export default 42; | ||||
export {x}; | ||||
export {v as x}; | ||||
export {x} from "mod"; | ||||
export {v as x} from "mod"; | ||||
export * from "mod"; | ||||
export * as ns from "mod"; |
The following definitions specify the required concrete methods and other
16.2.1.6.1 ParseModule (sourceText,realm,hostDefined )
The abstract operation ParseModule takes argumentssourceText (
- Letbody be
ParseText (sourceText,Module ). - Ifbody is a
List of errors, returnbody. - LetrequestedModules be the
ModuleRequests ofbody. - LetimportEntries be
ImportEntries ofbody. - LetimportedBoundNames be
ImportedLocalNames (importEntries). - LetindirectExportEntries be a new empty
List . - LetlocalExportEntries be a new empty
List . - LetstarExportEntries be a new empty
List . - LetexportEntries be
ExportEntries ofbody. - For each
ExportEntry Record ee ofexportEntries, do- Ifee.[[ModuleRequest]] is
null , then- IfimportedBoundNames does not containee.[[LocalName]], then
- Appendee tolocalExportEntries.
- Else,
- Letie be the element ofimportEntries whose[[LocalName]] isee.[[LocalName]].
- Ifie.[[ImportName]] is
namespace-object , then- NOTE: This is a re-export of an imported module namespace object.
- Appendee tolocalExportEntries.
- Else,
- NOTE: This is a re-export of a single name.
- Append the
ExportEntry Record {[[ModuleRequest]]:ie.[[ModuleRequest]],[[ImportName]]:ie.[[ImportName]],[[LocalName]]:null ,[[ExportName]]:ee.[[ExportName]] } toindirectExportEntries.
- IfimportedBoundNames does not containee.[[LocalName]], then
- Else ifee.[[ImportName]] is
all-but-default , thenAssert :ee.[[ExportName]] isnull .- Appendee tostarExportEntries.
- Else,
- Appendee toindirectExportEntries.
- Ifee.[[ModuleRequest]] is
- Letasync bebody
Contains await. - Return
Source Text Module Record {[[Realm]]:realm,[[Environment]]:empty ,[[Namespace]]:empty ,[[CycleRoot]]:empty ,[[HasTLA]]:async,[[AsyncEvaluation]]:false ,[[TopLevelCapability]]:empty ,[[AsyncParentModules]]: « »,[[PendingAsyncDependencies]]:empty ,[[Status]]:new ,[[EvaluationError]]:empty ,[[HostDefined]]:hostDefined,[[ECMAScriptCode]]:body,[[Context]]:empty ,[[ImportMeta]]:empty ,[[RequestedModules]]:requestedModules,[[LoadedModules]]: « »,[[ImportEntries]]:importEntries,[[LocalExportEntries]]:localExportEntries,[[IndirectExportEntries]]:indirectExportEntries,[[StarExportEntries]]:starExportEntries,[[DFSIndex]]:empty ,[[DFSAncestorIndex]]:empty }.
An implementation may parse module source text and analyse it for Early Error conditions prior to the evaluation of ParseModule for that module source text. However, the reporting of any errors must be deferred until the point where this specification actually performs ParseModule upon that source text.
16.2.1.6.2 GetExportedNames ( [exportStarSet ] )
The GetExportedNames concrete method of a
Assert :module.[[Status]] is notnew .- IfexportStarSet is not present, setexportStarSet to a new empty
List . - IfexportStarSet containsmodule, then
- Appendmodule toexportStarSet.
- LetexportedNames be a new empty
List . - For each
ExportEntry Record e ofmodule.[[LocalExportEntries]], do - For each
ExportEntry Record e ofmodule.[[IndirectExportEntries]], do - For each
ExportEntry Record e ofmodule.[[StarExportEntries]], doAssert :e.[[ModuleRequest]] is notnull .- LetrequestedModule be
GetImportedModule (module,e.[[ModuleRequest]]). - LetstarNames berequestedModule.GetExportedNames(exportStarSet).
- For each elementn ofstarNames, do
- If
SameValue (n,"default" ) isfalse , then- IfexportedNames does not containn, then
- Appendn toexportedNames.
- IfexportedNames does not containn, then
- If
- ReturnexportedNames.
GetExportedNames does not filter out or throw an exception for names that have ambiguous star export bindings.
16.2.1.6.3 ResolveExport (exportName [ ,resolveSet ] )
The ResolveExport concrete method of a
ResolveExport attempts to resolve an imported binding to the actual defining module and local binding name. The defining module may be the module represented by the
If a defining module is found, a
It performs the following steps when called:
Assert :module.[[Status]] is notnew .- IfresolveSet is not present, setresolveSet to a new empty
List . - For each
Record {[[Module]],[[ExportName]] }r ofresolveSet, do- Ifmodule andr.[[Module]] are the same
Module Record andSameValue (exportName,r.[[ExportName]]) istrue , thenAssert : This is a circular import request.- Return
null .
- Ifmodule andr.[[Module]] are the same
- Append the
Record {[[Module]]:module,[[ExportName]]:exportName } toresolveSet. - For each
ExportEntry Record e ofmodule.[[LocalExportEntries]], do- If
SameValue (exportName,e.[[ExportName]]) istrue , thenAssert :module provides the direct binding for this export.- Return
ResolvedBinding Record {[[Module]]:module,[[BindingName]]:e.[[LocalName]] }.
- If
- For each
ExportEntry Record e ofmodule.[[IndirectExportEntries]], do- If
SameValue (exportName,e.[[ExportName]]) istrue , thenAssert :e.[[ModuleRequest]] is notnull .- LetimportedModule be
GetImportedModule (module,e.[[ModuleRequest]]). - Ife.[[ImportName]] is
all , thenAssert :module does not provide the direct binding for this export.- Return
ResolvedBinding Record {[[Module]]:importedModule,[[BindingName]]:namespace }.
- Else,
Assert :module imports a specific binding for this export.- ReturnimportedModule.ResolveExport(e.[[ImportName]],resolveSet).
- If
- If
SameValue (exportName,"default" ) istrue , thenAssert : Adefaultexport was not explicitly defined by this module.- Return
null . - NOTE: A
defaultexport cannot be provided by anexport * from "mod"declaration.
- LetstarResolution be
null . - For each
ExportEntry Record e ofmodule.[[StarExportEntries]], doAssert :e.[[ModuleRequest]] is notnull .- LetimportedModule be
GetImportedModule (module,e.[[ModuleRequest]]). - Letresolution beimportedModule.ResolveExport(exportName,resolveSet).
- Ifresolution is
ambiguous , returnambiguous . - Ifresolution is not
null , thenAssert :resolution is aResolvedBinding Record .- IfstarResolution is
null , then- SetstarResolution toresolution.
- Else,
Assert : There is more than one*import that includes the requested name.- Ifresolution.[[Module]] andstarResolution.[[Module]] are not the same
Module Record , returnambiguous . - Ifresolution.[[BindingName]] is notstarResolution.[[BindingName]] and eitherresolution.[[BindingName]] orstarResolution.[[BindingName]] is
namespace , returnambiguous . - Ifresolution.[[BindingName]]
is a String ,starResolution.[[BindingName]]is a String , andSameValue (resolution.[[BindingName]],starResolution.[[BindingName]]) isfalse , returnambiguous .
- ReturnstarResolution.
16.2.1.6.4 InitializeEnvironment ( )
The InitializeEnvironment concrete method of a
- For each
ExportEntry Record e ofmodule.[[IndirectExportEntries]], doAssert :e.[[ExportName]] is notnull .- Letresolution bemodule.ResolveExport(e.[[ExportName]]).
- Ifresolution is either
null orambiguous , throw aSyntaxError exception. Assert :resolution is aResolvedBinding Record .
Assert : All named exports frommodule are resolvable.- Letrealm bemodule.[[Realm]].
Assert :realm is notundefined .- Letenv be
NewModuleEnvironment (realm.[[GlobalEnv]]). - Setmodule.[[Environment]] toenv.
- For each
ImportEntry Record in ofmodule.[[ImportEntries]], do- LetimportedModule be
GetImportedModule (module,in.[[ModuleRequest]]). - Ifin.[[ImportName]] is
namespace-object , then- Letnamespace be
GetModuleNamespace (importedModule). - Perform ! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]],namespace).
- Letnamespace be
- Else,
- Letresolution beimportedModule.ResolveExport(in.[[ImportName]]).
- Ifresolution is either
null orambiguous , throw aSyntaxError exception. - Ifresolution.[[BindingName]] is
namespace , then- Letnamespace be
GetModuleNamespace (resolution.[[Module]]). - Perform ! env.CreateImmutableBinding(in.[[LocalName]],
true ). - Perform ! env.InitializeBinding(in.[[LocalName]],namespace).
- Letnamespace be
- Else,
- Performenv.CreateImportBinding(in.[[LocalName]],resolution.[[Module]],resolution.[[BindingName]]).
- LetimportedModule be
- LetmoduleContext be a new
ECMAScript code execution context . - Set the Function ofmoduleContext to
null . Assert :module.[[Realm]] is notundefined .- Set the
Realm ofmoduleContext tomodule.[[Realm]]. - Set the ScriptOrModule ofmoduleContext tomodule.
- Set the VariableEnvironment ofmoduleContext tomodule.[[Environment]].
- Set the LexicalEnvironment ofmoduleContext tomodule.[[Environment]].
- Set the PrivateEnvironment ofmoduleContext to
null . - Setmodule.[[Context]] tomoduleContext.
- PushmoduleContext onto the
execution context stack ;moduleContext is now therunning execution context . - Letcode bemodule.[[ECMAScriptCode]].
- LetvarDeclarations be the
VarScopedDeclarations ofcode. - LetdeclaredVarNames be a new empty
List . - For each elementd ofvarDeclarations, do
- For each elementdn of the
BoundNames ofd, do- IfdeclaredVarNames does not containdn, then
- Perform ! env.CreateMutableBinding(dn,
false ). - Perform ! env.InitializeBinding(dn,
undefined ). - Appenddn todeclaredVarNames.
- Perform ! env.CreateMutableBinding(dn,
- IfdeclaredVarNames does not containdn, then
- For each elementdn of the
- LetlexDeclarations be the
LexicallyScopedDeclarations ofcode. - LetprivateEnv be
null . - For each elementd oflexDeclarations, do
- For each elementdn of the
BoundNames ofd, do- If
IsConstantDeclaration ofd istrue , then- Perform ! env.CreateImmutableBinding(dn,
true ).
- Perform ! env.CreateImmutableBinding(dn,
- Else,
- Perform ! env.CreateMutableBinding(dn,
false ).
- Perform ! env.CreateMutableBinding(dn,
- Ifd is either a
FunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration , then- Letfo be
InstantiateFunctionObject ofd with argumentsenv andprivateEnv. - Perform ! env.InitializeBinding(dn,fo).
- Letfo be
- If
- For each elementdn of the
- RemovemoduleContext from the
execution context stack . - Return
unused .
16.2.1.6.5 ExecuteModule ( [capability ] )
The ExecuteModule concrete method of a
- LetmoduleContext be a new
ECMAScript code execution context . - Set the Function ofmoduleContext to
null . - Set the
Realm ofmoduleContext tomodule.[[Realm]]. - Set the ScriptOrModule ofmoduleContext tomodule.
Assert :module has been linked and declarations in its module environment have been instantiated.- Set the VariableEnvironment ofmoduleContext tomodule.[[Environment]].
- Set the LexicalEnvironment ofmoduleContext tomodule.[[Environment]].
- Suspend the
running execution context . - Ifmodule.[[HasTLA]] is
false , thenAssert :capability is not present.- PushmoduleContext onto the
execution context stack ;moduleContext is now therunning execution context . - Letresult be
Completion (Evaluation ofmodule.[[ECMAScriptCode]]). - SuspendmoduleContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Ifresult is an
abrupt completion , then- Return ? result.
- Else,
Assert :capability is aPromiseCapability Record .- Perform
AsyncBlockStart (capability,module.[[ECMAScriptCode]],moduleContext).
- Return
unused .
16.2.1.7 GetImportedModule (referrer,specifier )
The abstract operation GetImportedModule takes argumentsreferrer (a
Assert : Exactly one element ofreferrer.[[LoadedModules]] is aRecord whose[[Specifier]] isspecifier, since LoadRequestedModules has completed successfully onreferrer prior to invoking this abstract operation.- Letrecord be the
Record inreferrer.[[LoadedModules]] whose[[Specifier]] isspecifier. - Returnrecord.[[Module]].
16.2.1.8 HostLoadImportedModule (referrer,specifier,hostDefined,payload )
The
An example of whenreferrer can be a
<buttontype="button"onclick="import('./foo.mjs')">Click me</button>there will be noimport()
An implementation of HostLoadImportedModule must conform to the following requirements:
- The
host environment must performFinishLoadingImportedModule (referrer,specifier,payload,result), whereresult is either anormal completion containing the loadedModule Record or athrow completion , either synchronously or asynchronously. - If this operation is called multiple times with the same (referrer,specifier) pair and it performs
FinishLoadingImportedModule (referrer,specifier,payload,result) whereresult is anormal completion , then it must performFinishLoadingImportedModule (referrer,specifier,payload,result) with the sameresult each time. - The operation must treatpayload as an opaque value to be passed through to
FinishLoadingImportedModule .
The actual process performed is
16.2.1.9 FinishLoadingImportedModule (referrer,specifier,payload,result )
The abstract operation FinishLoadingImportedModule takes argumentsreferrer (a
- Ifresult is a
normal completion , then - Ifpayload is a
GraphLoadingState Record , then- Perform
ContinueModuleLoading (payload,result).
- Perform
- Else,
- Perform
ContinueDynamicImport (payload,result).
- Perform
- Return
unused .
16.2.1.10 GetModuleNamespace (module )
The abstract operation GetModuleNamespace takes argumentmodule (an instance of a concrete subclass of
Assert : Ifmodule is aCyclic Module Record , thenmodule.[[Status]] is notnew orunlinked .- Letnamespace bemodule.[[Namespace]].
- Ifnamespace is
empty , then- LetexportedNames bemodule.GetExportedNames().
- LetunambiguousNames be a new empty
List . - For each elementname ofexportedNames, do
- Letresolution bemodule.ResolveExport(name).
- Ifresolution is a
ResolvedBinding Record , appendname tounambiguousNames.
- Setnamespace to
ModuleNamespaceCreate (module,unambiguousNames).
- Returnnamespace.
GetModuleNamespace never throws. Instead, unresolvable names are simply excluded from the namespace at this point. They will lead to a real linking error later unless they are all ambiguous star exports that are not explicitly requested anywhere.
16.2.1.11 Runtime Semantics: Evaluation
- Return
undefined .
- Letresult be
Completion (Evaluation ofModuleItemList ). - Ifresult is a
normal completion andresult.[[Value]] isempty , then- Return
undefined .
- Return
- Return ? result.
- Letsl be ?
Evaluation ofModuleItemList . - Lets be
Completion (Evaluation ofModuleItem ). - Return ?
UpdateEmpty (s,sl).
The value of a
- Return
empty .
16.2.2 Imports
Syntax
16.2.2.1 Static Semantics: Early Errors
- It is a Syntax Error if the
BoundNames ofImportDeclaration contains any duplicate entries.
16.2.2.2 Static Semantics: ImportEntries
The
- Return a new empty
List .
- Letentries1 be
ImportEntries ofModuleItemList . - Letentries2 be
ImportEntries ofModuleItem . - Return the
list-concatenation ofentries1 andentries2.
- Return a new empty
List .
- Letmodule be the sole element of
ModuleRequests ofFromClause . - Return
ImportEntriesForModule ofImportClause with argumentmodule.
- Return a new empty
List .
16.2.2.3 Static Semantics: ImportEntriesForModule
The
- Letentries1 be
ImportEntriesForModule ofImportedDefaultBinding with argumentmodule. - Letentries2 be
ImportEntriesForModule ofNameSpaceImport with argumentmodule. - Return the
list-concatenation ofentries1 andentries2.
- Letentries1 be
ImportEntriesForModule ofImportedDefaultBinding with argumentmodule. - Letentries2 be
ImportEntriesForModule ofNamedImports with argumentmodule. - Return the
list-concatenation ofentries1 andentries2.
- LetlocalName be the sole element of
BoundNames ofImportedBinding . - LetdefaultEntry be the
ImportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:"default" ,[[LocalName]]:localName }. - Return «defaultEntry ».
- LetlocalName be the
StringValue ofImportedBinding . - Letentry be the
ImportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:namespace-object ,[[LocalName]]:localName }. - Return «entry ».
- Return a new empty
List .
- Letspecs1 be the
ImportEntriesForModule ofImportsList with argumentmodule. - Letspecs2 be the
ImportEntriesForModule ofImportSpecifier with argumentmodule. - Return the
list-concatenation ofspecs1 andspecs2.
- LetlocalName be the sole element of
BoundNames ofImportedBinding . - Letentry be the
ImportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:localName,[[LocalName]]:localName }. - Return «entry ».
- LetimportName be the
StringValue ofModuleExportName . - LetlocalName be the
StringValue ofImportedBinding . - Letentry be the
ImportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:importName,[[LocalName]]:localName }. - Return «entry ».
16.2.3 Exports
Syntax
16.2.3.1 Static Semantics: Early Errors
- It is a Syntax Error if
ReferencedBindings ofNamedExports contains anyStringLiteral s. - For each
IdentifierName n inReferencedBindings ofNamedExports : It is a Syntax Error ifStringValue ofn is aReservedWord or theStringValue ofn is one of"implements" ,"interface" ,"let" ,"package" ,"private" ,"protected" ,"public" , or"static" .
The above rule means that each
16.2.3.2 Static Semantics: ExportedBindings
The
ExportedBindings are the locally bound names that are explicitly associated with a
It is defined piecewise over the following productions:
- Letnames1 be
ExportedBindings ofModuleItemList . - Letnames2 be
ExportedBindings ofModuleItem . - Return the
list-concatenation ofnames1 andnames2.
- Return a new empty
List .
- Return a new empty
List .
- Return the
ExportedBindings ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return the
BoundNames of thisExportDeclaration .
- Return a new empty
List .
- Letnames1 be the
ExportedBindings ofExportsList . - Letnames2 be the
ExportedBindings ofExportSpecifier . - Return the
list-concatenation ofnames1 andnames2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the firstModuleExportName .
16.2.3.3 Static Semantics: ExportedNames
The
ExportedNames are the externally visible names that a
It is defined piecewise over the following productions:
- Letnames1 be
ExportedNames ofModuleItemList . - Letnames2 be
ExportedNames ofModuleItem . - Return the
list-concatenation ofnames1 andnames2.
- Return the
ExportedNames ofExportDeclaration .
- Return a new empty
List .
- Return the
ExportedNames ofExportFromClause .
- Return a new empty
List .
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return the
ExportedNames ofNamedExports .
- Return the
BoundNames ofVariableStatement .
- Return the
BoundNames ofDeclaration .
- Return «
"default" ».
- Return a new empty
List .
- Letnames1 be the
ExportedNames ofExportsList . - Letnames2 be the
ExportedNames ofExportSpecifier . - Return the
list-concatenation ofnames1 andnames2.
- Return a
List whose sole element is theStringValue ofModuleExportName .
- Return a
List whose sole element is theStringValue of the secondModuleExportName .
16.2.3.4 Static Semantics: ExportEntries
The
- Return a new empty
List .
- Letentries1 be
ExportEntries ofModuleItemList . - Letentries2 be
ExportEntries ofModuleItem . - Return the
list-concatenation ofentries1 andentries2.
- Return a new empty
List .
- Letmodule be the sole element of
ModuleRequests ofFromClause . - Return
ExportEntriesForModule ofExportFromClause with argumentmodule.
- Return
ExportEntriesForModule ofNamedExports with argumentnull .
- Letentries be a new empty
List . - Letnames be the
BoundNames ofVariableStatement . - For each elementname ofnames, do
- Append the
ExportEntry Record {[[ModuleRequest]]:null ,[[ImportName]]:null ,[[LocalName]]:name,[[ExportName]]:name } toentries.
- Append the
- Returnentries.
- Letentries be a new empty
List . - Letnames be the
BoundNames ofDeclaration . - For each elementname ofnames, do
- Append the
ExportEntry Record {[[ModuleRequest]]:null ,[[ImportName]]:null ,[[LocalName]]:name,[[ExportName]]:name } toentries.
- Append the
- Returnentries.
- Letnames be
BoundNames ofHoistableDeclaration . - LetlocalName be the sole element ofnames.
- Return a
List whose sole element is a newExportEntry Record {[[ModuleRequest]]:null ,[[ImportName]]:null ,[[LocalName]]:localName,[[ExportName]]:"default" }.
- Letnames be
BoundNames ofClassDeclaration . - LetlocalName be the sole element ofnames.
- Return a
List whose sole element is a newExportEntry Record {[[ModuleRequest]]:null ,[[ImportName]]:null ,[[LocalName]]:localName,[[ExportName]]:"default" }.
- Letentry be the
ExportEntry Record {[[ModuleRequest]]:null ,[[ImportName]]:null ,[[LocalName]]:"*default*" ,[[ExportName]]:"default" }. - Return «entry ».
16.2.3.5 Static Semantics: ExportEntriesForModule
The
- Letentry be the
ExportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:all-but-default ,[[LocalName]]:null ,[[ExportName]]:null }. - Return «entry ».
- LetexportName be the
StringValue ofModuleExportName . - Letentry be the
ExportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:all ,[[LocalName]]:null ,[[ExportName]]:exportName }. - Return «entry ».
- Return a new empty
List .
- Letspecs1 be the
ExportEntriesForModule ofExportsList with argumentmodule. - Letspecs2 be the
ExportEntriesForModule ofExportSpecifier with argumentmodule. - Return the
list-concatenation ofspecs1 andspecs2.
- LetsourceName be the
StringValue ofModuleExportName . - Ifmodule is
null , then- LetlocalName besourceName.
- LetimportName be
null .
- Else,
- LetlocalName be
null . - LetimportName besourceName.
- LetlocalName be
- Return a
List whose sole element is a newExportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:importName,[[LocalName]]:localName,[[ExportName]]:sourceName }.
- LetsourceName be the
StringValue of the firstModuleExportName . - LetexportName be the
StringValue of the secondModuleExportName . - Ifmodule is
null , then- LetlocalName besourceName.
- LetimportName be
null .
- Else,
- LetlocalName be
null . - LetimportName besourceName.
- LetlocalName be
- Return a
List whose sole element is a newExportEntry Record {[[ModuleRequest]]:module,[[ImportName]]:importName,[[LocalName]]:localName,[[ExportName]]:exportName }.
16.2.3.6 Static Semantics: ReferencedBindings
The
- Return a new empty
List .
- Letnames1 be the
ReferencedBindings ofExportsList . - Letnames2 be the
ReferencedBindings ofExportSpecifier . - Return the
list-concatenation ofnames1 andnames2.
- Return the
ReferencedBindings of the firstModuleExportName .
- Return a
List whose sole element is theIdentifierName .
- Return a
List whose sole element is theStringLiteral .
16.2.3.7 Runtime Semantics: Evaluation
- Return
empty .
- Return ?
Evaluation ofVariableStatement .
- Return ?
Evaluation ofDeclaration .
- Return ?
Evaluation ofHoistableDeclaration .
- Letvalue be ?
BindingClassDeclarationEvaluation ofClassDeclaration . - LetclassName be the sole element of
BoundNames ofClassDeclaration . - IfclassName is
"*default*" , then- Letenv be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" ,value,env).
- Letenv be the
- Return
empty .
- If
IsAnonymousFunctionDefinition (AssignmentExpression ) istrue , then- Letvalue be ?
NamedEvaluation ofAssignmentExpression with argument"default" .
- Letvalue be ?
- Else,
- Letrhs be ?
Evaluation ofAssignmentExpression . - Letvalue be ?
GetValue (rhs).
- Letrhs be ?
- Letenv be the
running execution context 's LexicalEnvironment. - Perform ?
InitializeBoundName ("*default*" ,value,env). - Return
empty .
17 Error Handling and Language Extensions
An implementation must report most errors at the time the relevant ECMAScript language construct is evaluated. Anearly error is an error that can be detected and reported prior to the evaluation of any construct in theeval is called and prevent evaluation of theeval code. All errors that are not
An implementation must report as an
An implementation shall not treat other kinds of errors as
An implementation shall report all errors as specified, except for the following:
- Except as restricted in
17.1 , ahost or implementation may extendScript syntax,Module syntax, and regular expression pattern or flag syntax. To permit this, all operations (such as callingeval, using a regular expression literal, or using the Function or RegExpconstructor ) that are allowed to throwSyntaxError are permitted to exhibithost-defined behaviour instead of throwingSyntaxError when they encounter ahost-defined extension to the script syntax or regular expression pattern or flag syntax. - Except as restricted in
17.1 , ahost or implementation may provide additional types, values, objects, properties, and functions beyond those described in this specification. This may cause constructs (such as looking up a variable in the global scope) to havehost-defined behaviour instead of throwing an error (such asReferenceError ).
17.1 Forbidden Extensions
An implementation must not extend this specification in the following ways:
- ECMAScript
function objects defined using syntacticconstructors instrict mode code must not be created with own properties named"caller" or"arguments" . Such own properties also must not be created forfunction objects defined using anArrowFunction ,MethodDefinition ,GeneratorDeclaration ,GeneratorExpression ,AsyncGeneratorDeclaration ,AsyncGeneratorExpression ,ClassDeclaration ,ClassExpression ,AsyncFunctionDeclaration ,AsyncFunctionExpression , orAsyncArrowFunction regardless of whether the definition is contained instrict mode code . Built-in functions,strict functions created using the Functionconstructor , generator functions created using the Generatorconstructor , async functions created using the AsyncFunctionconstructor , and functions created using thebindmethod also must not be created with such own properties. - If an implementation extends any
function object with an own property named"caller" the value of that property, as observed using[[Get]] or[[GetOwnProperty]], must not be astrict function object. If it is anaccessor property , the function that is the value of the property's[[Get]] attribute must never return astrict function when called. - Neither mapped nor unmapped arguments objects may be created with an own property named
"caller" . - The behaviour of built-in methods which are specified in ECMA-402, such as those named
toLocaleString, must not be extended except as specified in ECMA-402. - The RegExp pattern grammars in
22.2.1 andB.1.2 must not be extended to recognize any of the source characters A-Z or a-z asIdentityEscape when the[UnicodeMode] grammar parameter is present.[+UnicodeMode] - The Syntactic Grammar must not be extended in any manner that allows the token
:to immediately follow source text that is matched by theBindingIdentifier nonterminal symbol. - When processing
strict mode code , an implementation must not relax theearly error rules of12.9.3.1 . TemplateEscapeSequence must not be extended to includeLegacyOctalEscapeSequence orNonOctalDecimalEscapeSequence as defined in12.9.4 .- When processing
strict mode code , the extensions defined inB.3.1 ,B.3.2 ,B.3.3 , andB.3.5 must not be supported. - When parsing for the
Module goal symbol , the lexical grammar extensions defined inB.1.1 must not be supported. ImportCall must not be extended.
18 ECMAScript Standard Built-in Objects
There are certain built-in objects available whenever an ECMAScript
Unless specified otherwise, a built-in object that is callable as a function is a built-in
Many built-in objects are functions: they can be invoked with arguments. Some of them furthermore arenew operator. For each built-in function, this specification describes the arguments required by that function and the properties of thatnew expression that invokes that
Unless otherwise specified in the description of a particular function, if a built-in function or
Unless otherwise specified in the description of a particular function, if a built-in function or
Implementations that add additional capabilities to the set of built-in functions are encouraged to do so by adding new functions rather than adding new parameters to existing functions.
Unless otherwise specified every built-in function and every built-inFunction.prototype (
Unless otherwise specified every built-in prototype object has theObject.prototype (
If this specification defines a built-in
Built-in
Built-in
Each built-in function defined in this specification is created by calling the
Every built-in
For example, the
Unless otherwise specified, the
Every built-in
The value of the
Unless otherwise specified, the
Every other
Every
19 The Global Object
Theglobal object:
- is created before control enters any
execution context . - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a[[Call]] internal method; it cannot be invoked as a function.
- has a[[Prototype]] internal slot whose value is
host-defined . - may have
host-defined properties in addition to the properties defined in this specification. This may include a property whose value is the global object itself.
19.1 Value Properties of the Global Object
19.1.1 globalThis
The initial value of the
This property has the attributes {[[Writable]]:
19.1.2 Infinity
The value ofInfinity is
19.1.3 NaN
The value ofNaN is
19.1.4 undefined
The value ofundefined is
19.2 Function Properties of the Global Object
19.2.1 eval (x )
This function is the%eval% intrinsic object.
It performs the following steps when called:
- Return ?
PerformEval (x,false ,false ).
19.2.1.1 PerformEval (x,strictCaller,direct )
The abstract operation PerformEval takes argumentsx (an
Assert : Ifdirect isfalse , thenstrictCaller is alsofalse .- Ifx
is not a String , returnx. - LetevalRealm be
the current Realm Record . - NOTE: In the case of a
direct eval ,evalRealm is therealm of both the caller ofevaland of theevalfunction itself. - Perform ?
HostEnsureCanCompileStrings (evalRealm, « »,x,direct). - LetinFunction be
false . - LetinMethod be
false . - LetinDerivedConstructor be
false . - LetinClassFieldInitializer be
false . - Ifdirect is
true , then- LetthisEnvRec be
GetThisEnvironment (). - IfthisEnvRec is a
Function Environment Record , then- LetF bethisEnvRec.[[FunctionObject]].
- SetinFunction to
true . - SetinMethod tothisEnvRec.HasSuperBinding().
- IfF.[[ConstructorKind]] is
derived , setinDerivedConstructor totrue . - LetclassFieldInitializerName beF.[[ClassFieldInitializerName]].
- IfclassFieldInitializerName is not
empty , setinClassFieldInitializer totrue .
- LetthisEnvRec be
- Perform the following substeps in an
implementation-defined order, possibly interleaving parsing and error detection:- Letscript be
ParseText (StringToCodePoints (x),Script ). - Ifscript is a
List of errors, throw aSyntaxError exception. - Ifscript
Contains ScriptBody isfalse , returnundefined . - Letbody be the
ScriptBody ofscript. - IfinFunction is
false andbodyContains NewTarget , throw aSyntaxError exception. - IfinMethod is
false andbodyContains SuperProperty , throw aSyntaxError exception. - IfinDerivedConstructor is
false andbodyContains SuperCall , throw aSyntaxError exception. - IfinClassFieldInitializer is
true andContainsArguments ofbody istrue , throw aSyntaxError exception.
- Letscript be
- IfstrictCaller is
true , letstrictEval betrue . - Else, letstrictEval be
IsStrict ofscript. - LetrunningContext be the
running execution context . - NOTE: Ifdirect is
true ,runningContext will be theexecution context that performed thedirect eval . Ifdirect isfalse ,runningContext will be theexecution context for the invocation of theevalfunction. - Ifdirect is
true , then- LetlexEnv be
NewDeclarativeEnvironment (runningContext's LexicalEnvironment). - LetvarEnv berunningContext's VariableEnvironment.
- LetprivateEnv berunningContext's PrivateEnvironment.
- LetlexEnv be
- Else,
- LetlexEnv be
NewDeclarativeEnvironment (evalRealm.[[GlobalEnv]]). - LetvarEnv beevalRealm.[[GlobalEnv]].
- LetprivateEnv be
null .
- LetlexEnv be
- IfstrictEval is
true , setvarEnv tolexEnv. - IfrunningContext is not already suspended, suspendrunningContext.
- LetevalContext be a new
ECMAScript code execution context . - SetevalContext's Function to
null . - SetevalContext's
Realm toevalRealm. - SetevalContext's ScriptOrModule torunningContext's ScriptOrModule.
- SetevalContext's VariableEnvironment tovarEnv.
- SetevalContext's LexicalEnvironment tolexEnv.
- SetevalContext's PrivateEnvironment toprivateEnv.
- PushevalContext onto the
execution context stack ;evalContext is now therunning execution context . - Letresult be
Completion (EvalDeclarationInstantiation (body,varEnv,lexEnv,privateEnv,strictEval)). - Ifresult is a
normal completion , then- Setresult to
Completion (Evaluation ofbody).
- Setresult to
- Ifresult is a
normal completion andresult.[[Value]] isempty , then- Setresult to
NormalCompletion (undefined ).
- Setresult to
- SuspendevalContext and remove it from the
execution context stack . - Resume the context that is now on the top of the
execution context stack as therunning execution context . - Return ? result.
The eval code cannot instantiate variable or function bindings in the variable environment of the calling context that invoked the eval if either the code of the calling context or the eval code islet,const, orclass declarations are always instantiated in a new LexicalEnvironment.
19.2.1.2 HostEnsureCanCompileStrings (calleeRealm,parameterStrings,bodyString,direct )
The
parameterStrings represents the strings that, when using one of the functioneval call.direct signifies whether the evaluation is a
The default implementation of HostEnsureCanCompileStrings is to return
19.2.1.3 EvalDeclarationInstantiation (body,varEnv,lexEnv,privateEnv,strict )
The abstract operation EvalDeclarationInstantiation takes argumentsbody (a
- LetvarNames be the
VarDeclaredNames ofbody. - LetvarDeclarations be the
VarScopedDeclarations ofbody. - Ifstrict is
false , then- IfvarEnv is a
Global Environment Record , then- For each elementname ofvarNames, do
- IfvarEnv.HasLexicalDeclaration(name) is
true , throw aSyntaxError exception. - NOTE:
evalwill not create a global var declaration that would be shadowed by a global lexical declaration.
- IfvarEnv.HasLexicalDeclaration(name) is
- For each elementname ofvarNames, do
- LetthisEnv belexEnv.
Assert : The following loop will terminate.- Repeat, whilethisEnv is notvarEnv,
- IfthisEnv
is not an Object Environment Record , then- NOTE: The environment of with statements cannot contain any lexical declaration so it doesn't need to be checked for var/let hoisting conflicts.
- For each elementname ofvarNames, do
- If ! thisEnv.HasBinding(name) is
true , then- Throw a
SyntaxError exception. - NOTE: Annex
B.3.4 defines alternate semantics for the above step.
- Throw a
- NOTE: A
direct eval will not hoist var declaration over a like-named lexical declaration.
- If ! thisEnv.HasBinding(name) is
- SetthisEnv tothisEnv.[[OuterEnv]].
- IfthisEnv
- IfvarEnv is a
- LetprivateIdentifiers be a new empty
List . - Letpointer beprivateEnv.
- Repeat, whilepointer is not
null ,- For each
Private Name binding ofpointer.[[Names]], do- IfprivateIdentifiers does not containbinding.[[Description]], appendbinding.[[Description]] toprivateIdentifiers.
- Setpointer topointer.[[OuterPrivateEnvironment]].
- For each
- If
AllPrivateIdentifiersValid ofbody with argumentprivateIdentifiers isfalse , throw aSyntaxError exception. - LetfunctionsToInitialize be a new empty
List . - LetdeclaredFunctionNames be a new empty
List . - For each elementd ofvarDeclarations, in reverse
List order, do- Ifd is not either a
VariableDeclaration , aForBinding , or aBindingIdentifier , thenAssert :d is either aFunctionDeclaration , aGeneratorDeclaration , anAsyncFunctionDeclaration , or anAsyncGeneratorDeclaration .- NOTE: If there are multiple function declarations for the same name, the last declaration is used.
- Letfn be the sole element of the
BoundNames ofd. - IfdeclaredFunctionNames does not containfn, then
- IfvarEnv is a
Global Environment Record , then- LetfnDefinable be ? varEnv.CanDeclareGlobalFunction(fn).
- IffnDefinable is
false , throw aTypeError exception.
- Appendfn todeclaredFunctionNames.
- Insertd as the first element offunctionsToInitialize.
- IfvarEnv is a
- Ifd is not either a
- LetdeclaredVarNames be a new empty
List . - For each elementd ofvarDeclarations, do
- Ifd is either a
VariableDeclaration , aForBinding , or aBindingIdentifier , then- For each Stringvn of the
BoundNames ofd, do- IfdeclaredFunctionNames does not containvn, then
- IfvarEnv is a
Global Environment Record , then- LetvnDefinable be ? varEnv.CanDeclareGlobalVar(vn).
- IfvnDefinable is
false , throw aTypeError exception.
- IfdeclaredVarNames does not containvn, then
- Appendvn todeclaredVarNames.
- IfvarEnv is a
- IfdeclaredFunctionNames does not containvn, then
- For each Stringvn of the
- Ifd is either a
- NOTE: Annex
B.3.2.3 adds additional steps at this point. - NOTE: No abnormal terminations occur after this algorithm step unlessvarEnv is a
Global Environment Record and theglobal object is aProxy exotic object . - LetlexDeclarations be the
LexicallyScopedDeclarations ofbody. - For each elementd oflexDeclarations, do
- NOTE: Lexically declared names are only instantiated here but not initialized.
- For each elementdn of the
BoundNames ofd, do- If
IsConstantDeclaration ofd istrue , then- Perform ? lexEnv.CreateImmutableBinding(dn,
true ).
- Perform ? lexEnv.CreateImmutableBinding(dn,
- Else,
- Perform ? lexEnv.CreateMutableBinding(dn,
false ).
- Perform ? lexEnv.CreateMutableBinding(dn,
- If
- For each
Parse Node f offunctionsToInitialize, do- Letfn be the sole element of the
BoundNames off. - Letfo be
InstantiateFunctionObject off with argumentslexEnv andprivateEnv. - IfvarEnv is a
Global Environment Record , then- Perform ? varEnv.CreateGlobalFunctionBinding(fn,fo,
true ).
- Perform ? varEnv.CreateGlobalFunctionBinding(fn,fo,
- Else,
- LetbindingExists be ! varEnv.HasBinding(fn).
- IfbindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform ! varEnv.CreateMutableBinding(fn,
true ). - Perform ! varEnv.InitializeBinding(fn,fo).
- NOTE: The following invocation cannot return an
- Else,
- Perform ! varEnv.SetMutableBinding(fn,fo,
false ).
- Perform ! varEnv.SetMutableBinding(fn,fo,
- Letfn be the sole element of the
- For each Stringvn ofdeclaredVarNames, do
- IfvarEnv is a
Global Environment Record , then- Perform ? varEnv.CreateGlobalVarBinding(vn,
true ).
- Perform ? varEnv.CreateGlobalVarBinding(vn,
- Else,
- LetbindingExists be ! varEnv.HasBinding(vn).
- IfbindingExists is
false , then- NOTE: The following invocation cannot return an
abrupt completion because of the validation preceding step14 . - Perform ! varEnv.CreateMutableBinding(vn,
true ). - Perform ! varEnv.InitializeBinding(vn,
undefined ).
- NOTE: The following invocation cannot return an
- IfvarEnv is a
- Return
unused .
An alternative version of this algorithm is described in
19.2.2 isFinite (number )
This function is the%isFinite% intrinsic object.
It performs the following steps when called:
19.2.3 isNaN (number )
This function is the%isNaN% intrinsic object.
It performs the following steps when called:
- Letnum be ?
ToNumber (number). - Ifnum is
NaN , returntrue . - Otherwise, return
false .
A reliable way for ECMAScript code to test if a valueX isX !== X. The result will beX is
19.2.4 parseFloat (string )
This function produces a Number value dictated by interpretation of the contents of thestring argument as a decimal literal.
It is the%parseFloat% intrinsic object.
It performs the following steps when called:
- LetinputString be ?
ToString (string). - LettrimmedString be !
TrimString (inputString,start ). - Lettrimmed be
StringToCodePoints (trimmedString). - LettrimmedPrefix be the longest prefix oftrimmed that satisfies the syntax of a
StrDecimalLiteral , which might betrimmed itself. If there is no such prefix, returnNaN . - LetparsedNumber be
ParseText (trimmedPrefix,StrDecimalLiteral ). Assert :parsedNumber is aParse Node .- Return
StringNumericValue ofparsedNumber.
This function may interpret only a leading portion ofstring as a Number value; it ignores any code units that cannot be interpreted as part of the notation of a decimal literal, and no indication is given that any such code units were ignored.
19.2.5 parseInt (string,radix )
This function produces an
It is the%parseInt% intrinsic object.
It performs the following steps when called:
- LetinputString be ?
ToString (string). - LetS be !
TrimString (inputString,start ). - Letsign be 1.
- IfS is not empty and the first code unit ofS is the code unit 0x002D (HYPHEN-MINUS), setsign to -1.
- IfS is not empty and the first code unit ofS is either the code unit 0x002B (PLUS SIGN) or the code unit 0x002D (HYPHEN-MINUS), setS to the
substring ofS from index 1. - LetR be
ℝ (?ToInt32 (radix)). - LetstripPrefix be
true . - IfR ≠ 0, then
- IfR < 2 orR > 36, return
NaN . - IfR ≠ 16, setstripPrefix to
false .
- IfR < 2 orR > 36, return
- Else,
- SetR to 10.
- IfstripPrefix is
true , then- If the length ofS is at least 2 and the first two code units ofS are either
"0x" or"0X" , then- SetS to the
substring ofS from index 2. - SetR to 16.
- SetS to the
- If the length ofS is at least 2 and the first two code units ofS are either
- IfS contains a code unit that is not a radix-R digit, letend be the index withinS of the first such code unit; otherwise, letend be the length ofS.
- LetZ be the
substring ofS from 0 toend. - IfZ is empty, return
NaN . - LetmathInt be the
integer value that is represented byZ in radix-R notation, using the lettersA throughZ anda throughz for digits with values 10 through 35. (However, ifR = 10 andZ contains more than 20 significant digits, every significant digit after the 20th may be replaced by a 0 digit, at the option of the implementation; and ifR is not one of 2, 4, 8, 10, 16, or 32, thenmathInt may be animplementation-approximated integer representing theinteger value denoted byZ in radix-R notation.) - IfmathInt = 0, then
- Ifsign = -1, return
-0 𝔽. - Return
+0 𝔽.
- Ifsign = -1, return
- Return
𝔽 (sign ×mathInt).
19.2.6 URI Handling Functions
Uniform Resource Identifiers, or URIs, are Strings that identify resources (e.g. web pages or files) and transport protocols by which to access them (e.g. HTTP or FTP) on the Internet. The ECMAScript language itself does not provide any support for using URIs except for functions that encode and decode URIs as described in this section.encodeURI anddecodeURI are intended to work with complete URIs; they assume that any reserved characters are intended to have special meaning (e.g., as delimiters) and so are not encoded.encodeURIComponent anddecodeURIComponent are intended to work with the individual components of a URI; they assume that any reserved characters represent text and must be encoded to avoid special meaning when the component is part of a complete URI.
The set of reserved characters is based upon RFC 2396 and does not reflect changes introduced by the more recent RFC 3986.
Many implementations of ECMAScript provide additional functions and methods that manipulate web pages; these functions are beyond the scope of this standard.
19.2.6.1 decodeURI (encodedURI )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by theencodeURI function is replaced with the UTF-16 encoding of the code point that it represents. Escape sequences that could not have been introduced byencodeURI are not replaced.
It is the%decodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.2 decodeURIComponent (encodedURIComponent )
This function computes a new version of a URI in which each escape sequence and UTF-8 encoding of the sort that might be introduced by theencodeURIComponent function is replaced with the UTF-16 encoding of the code point that it represents.
It is the%decodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.3 encodeURI (uri )
This function computes a new version of a UTF-16 encoded (
It is the%encodeURI% intrinsic object.
It performs the following steps when called:
19.2.6.4 encodeURIComponent (uriComponent )
This function computes a new version of a UTF-16 encoded (
It is the%encodeURIComponent% intrinsic object.
It performs the following steps when called:
19.2.6.5 Encode (string,extraUnescaped )
The abstract operation Encode takes argumentsstring (a String) andextraUnescaped (a String) and returns either a
- Letlen be the length ofstring.
- LetR be the empty String.
- LetalwaysUnescaped be the
string-concatenation ofthe ASCII word characters and"-.!~*'()" . - LetunescapedSet be the
string-concatenation ofalwaysUnescaped andextraUnescaped. - Letk be 0.
- Repeat, whilek <len,
- LetC be the code unit at indexk withinstring.
- IfunescapedSet containsC, then
- Setk tok + 1.
- SetR to the
string-concatenation ofR andC.
- Else,
- Letcp be
CodePointAt (string,k). - Ifcp.[[IsUnpairedSurrogate]] is
true , throw aURIError exception. - Setk tok +cp.[[CodeUnitCount]].
- LetOctets be the
List of octets resulting by applying the UTF-8 transformation tocp.[[CodePoint]]. - For each elementoctet ofOctets, do
- Lethex be the String representation ofoctet, formatted as an uppercase hexadecimal number.
- SetR to the
string-concatenation ofR,"%" , andStringPad (hex, 2,"0" ,start ).
- Letcp be
- ReturnR.
Because percent-encoding is used to represent individual octets, a single code point may be expressed as multiple consecutive escape sequences (one for each of its 8-bit UTF-8 code units).
19.2.6.6 Decode (string,preserveEscapeSet )
The abstract operation Decode takes argumentsstring (a String) andpreserveEscapeSet (a String) and returns either a
- Letlen be the length ofstring.
- LetR be the empty String.
- Letk be 0.
- Repeat, whilek <len,
- LetC be the code unit at indexk withinstring.
- LetS beC.
- IfC is the code unit 0x0025 (PERCENT SIGN), then
- Ifk + 3 >len, throw a
URIError exception. - Letescape be the
substring ofstring fromk tok + 3. - LetB be
ParseHexOctet (string,k + 1). - IfB is not an
integer , throw aURIError exception. - Setk tok + 2.
- Letn be the number of leading 1 bits inB.
- Ifn = 0, then
- LetasciiChar be the code unit whose numeric value isB.
- IfpreserveEscapeSet containsasciiChar, setS toescape. Otherwise, setS toasciiChar.
- Else,
- Ifn = 1 orn > 4, throw a
URIError exception. - LetOctets be «B ».
- Letj be 1.
- Repeat, whilej <n,
- Setk tok + 1.
- Ifk + 3 >len, throw a
URIError exception. - If the code unit at indexk withinstring is not the code unit 0x0025 (PERCENT SIGN), throw a
URIError exception. - LetcontinuationByte be
ParseHexOctet (string,k + 1). - IfcontinuationByte is not an
integer , throw aURIError exception. - AppendcontinuationByte toOctets.
- Setk tok + 2.
- Setj toj + 1.
Assert : The length ofOctets isn.- IfOctets does not contain a valid UTF-8 encoding of a Unicode code point, throw a
URIError exception. - LetV be the code point obtained by applying the UTF-8 transformation toOctets, that is, from a
List of octets into a 21-bit value. - SetS to
UTF16EncodeCodePoint (V).
- Ifn = 1 orn > 4, throw a
- Ifk + 3 >len, throw a
- SetR to the
string-concatenation ofR andS. - Setk tok + 1.
- ReturnR.
RFC 3629 prohibits the decoding of invalid UTF-8 octet sequences. For example, the invalid sequence 0xC0 0x80 must not decode into the code unit 0x0000. Implementations of the Decode algorithm are required to throw a
19.2.6.7 ParseHexOctet (string,position )
The abstract operation ParseHexOctet takes argumentsstring (a String) andposition (a non-negative
- Letlen be the length ofstring.
Assert :position + 2 ≤len.- LethexDigits be the
substring ofstring fromposition toposition + 2. - LetparseResult be
ParseText (StringToCodePoints (hexDigits),HexDigits ).[~Sep] - IfparseResult is not a
Parse Node , returnparseResult. - Letn be the MV ofparseResult.
Assert :n is in theinclusive interval from 0 to 255.- Returnn.
19.3 Constructor Properties of the Global Object
19.3.1 AggregateError ( . . . )
See
19.3.2 Array ( . . . )
See
19.3.3 ArrayBuffer ( . . . )
See
19.3.4 BigInt ( . . . )
See
19.3.5 BigInt64Array ( . . . )
See
19.3.6 BigUint64Array ( . . . )
See
19.3.7 Boolean ( . . . )
See
19.3.8 DataView ( . . . )
See
19.3.9 Date ( . . . )
See
19.3.10 Error ( . . . )
See
19.3.11 EvalError ( . . . )
See
19.3.12 FinalizationRegistry ( . . . )
See
19.3.13 Float32Array ( . . . )
See
19.3.14 Float64Array ( . . . )
See
19.3.15 Function ( . . . )
See
19.3.16 Int8Array ( . . . )
See
19.3.17 Int16Array ( . . . )
See
19.3.18 Int32Array ( . . . )
See
19.3.19 Map ( . . . )
See
19.3.20 Number ( . . . )
See
19.3.21 Object ( . . . )
See
19.3.22 Promise ( . . . )
See
19.3.23 Proxy ( . . . )
See
19.3.24 RangeError ( . . . )
See
19.3.25 ReferenceError ( . . . )
See
19.3.26 RegExp ( . . . )
See
19.3.27 Set ( . . . )
See
19.3.28 SharedArrayBuffer ( . . . )
See
19.3.29 String ( . . . )
See
19.3.30 Symbol ( . . . )
See
19.3.31 SyntaxError ( . . . )
See
19.3.32 TypeError ( . . . )
See
19.3.33 Uint8Array ( . . . )
See
19.3.34 Uint8ClampedArray ( . . . )
See
19.3.35 Uint16Array ( . . . )
See
19.3.36 Uint32Array ( . . . )
See
19.3.37 URIError ( . . . )
See
19.3.38 WeakMap ( . . . )
See
19.3.39 WeakRef ( . . . )
See
19.3.40 WeakSet ( . . . )
See
19.4 Other Properties of the Global Object
19.4.1 Atomics
See
19.4.2 JSON
See
19.4.3 Math
See
19.4.4 Reflect
See
20 Fundamental Objects
20.1 Object Objects
20.1.1 The Object Constructor
The Object
- is%Object%.
- is the initial value of the
"Object" property of theglobal object . - creates a new
ordinary object when called as aconstructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition.
20.1.1.1 Object ( [value ] )
This function performs the following steps when called:
- If NewTarget is neither
undefined nor theactive function object , then- Return ?
OrdinaryCreateFromConstructor (NewTarget,"%Object.prototype%" ).
- Return ?
- Ifvalue is either
undefined ornull , returnOrdinaryObjectCreate (%Object.prototype% ). - Return !
ToObject (value).
20.1.2 Properties of the Object Constructor
The Object
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following additional properties:
20.1.2.1 Object.assign (target, ...sources )
This function copies the values of all of the enumerable own properties from one or more source objects to atarget object.
It performs the following steps when called:
- Letto be ?
ToObject (target). - If only one argument was passed, returnto.
- For each elementnextSource ofsources, do
- IfnextSource is neither
undefined nornull , then
- IfnextSource is neither
- Returnto.
The
20.1.2.2 Object.create (O,Properties )
This function creates a new object with a specified prototype.
It performs the following steps when called:
- IfO
is not an Object andO is notnull , throw aTypeError exception. - Letobj be
OrdinaryObjectCreate (O). - IfProperties is not
undefined , then- Return ?
ObjectDefineProperties (obj,Properties).
- Return ?
- Returnobj.
20.1.2.3 Object.defineProperties (O,Properties )
This function adds own properties and/or updates the attributes of existing own properties of an object.
It performs the following steps when called:
- IfO
is not an Object , throw aTypeError exception. - Return ?
ObjectDefineProperties (O,Properties).
20.1.2.3.1 ObjectDefineProperties (O,Properties )
The abstract operation ObjectDefineProperties takes argumentsO (an Object) andProperties (an
- Letprops be ?
ToObject (Properties). - Letkeys be ? props.[[OwnPropertyKeys]]().
- Letdescriptors be a new empty
List . - For each elementnextKey ofkeys, do
- LetpropDesc be ? props.[[GetOwnProperty]](nextKey).
- IfpropDesc is not
undefined andpropDesc.[[Enumerable]] istrue , then- LetdescObj be ?
Get (props,nextKey). - Letdesc be ?
ToPropertyDescriptor (descObj). - Append the
Record {[[Key]]:nextKey,[[Descriptor]]:desc } todescriptors.
- LetdescObj be ?
- For each elementproperty ofdescriptors, do
- Perform ?
DefinePropertyOrThrow (O,property.[[Key]],property.[[Descriptor]]).
- Perform ?
- ReturnO.
20.1.2.4 Object.defineProperty (O,P,Attributes )
This function adds an own property and/or updates the attributes of an existing own property of an object.
It performs the following steps when called:
- IfO
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (P). - Letdesc be ?
ToPropertyDescriptor (Attributes). - Perform ?
DefinePropertyOrThrow (O,key,desc). - ReturnO.
20.1.2.5 Object.entries (O )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - LetentryList be ?
EnumerableOwnProperties (obj,key+value ). - Return
CreateArrayFromList (entryList).
20.1.2.6 Object.freeze (O )
This function performs the following steps when called:
- IfO
is not an Object , returnO. - Letstatus be ?
SetIntegrityLevel (O,frozen ). - Ifstatus is
false , throw aTypeError exception. - ReturnO.
20.1.2.7 Object.fromEntries (iterable )
This function performs the following steps when called:
- Perform ?
RequireObjectCoercible (iterable). - Letobj be
OrdinaryObjectCreate (%Object.prototype% ). Assert :obj is an extensibleordinary object with no own properties.- Letclosure be a new
Abstract Closure with parameters (key,value) that capturesobj and performs the following steps when called:- LetpropertyKey be ?
ToPropertyKey (key). - Perform !
CreateDataPropertyOrThrow (obj,propertyKey,value). - Return
undefined .
- LetpropertyKey be ?
- Letadder be
CreateBuiltinFunction (closure, 2,"" , « »). - Return ?
AddEntriesFromIterable (obj,iterable,adder).
20.1.2.8 Object.getOwnPropertyDescriptor (O,P )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - Letkey be ?
ToPropertyKey (P). - Letdesc be ? obj.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
20.1.2.9 Object.getOwnPropertyDescriptors (O )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - LetownKeys be ? obj.[[OwnPropertyKeys]]().
- Letdescriptors be
OrdinaryObjectCreate (%Object.prototype% ). - For each elementkey ofownKeys, do
- Letdesc be ? obj.[[GetOwnProperty]](key).
- Letdescriptor be
FromPropertyDescriptor (desc). - Ifdescriptor is not
undefined , perform !CreateDataPropertyOrThrow (descriptors,key,descriptor).
- Returndescriptors.
20.1.2.10 Object.getOwnPropertyNames (O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,string )).
20.1.2.11 Object.getOwnPropertySymbols (O )
This function performs the following steps when called:
- Return
CreateArrayFromList (?GetOwnPropertyKeys (O,symbol )).
20.1.2.11.1 GetOwnPropertyKeys (O,type )
The abstract operation GetOwnPropertyKeys takes argumentsO (an
- Letobj be ?
ToObject (O). - Letkeys be ? obj.[[OwnPropertyKeys]]().
- LetnameList be a new empty
List . - For each elementnextKey ofkeys, do
- IfnextKey
is a Symbol andtype issymbol , or ifnextKeyis a String andtype isstring , then- AppendnextKey tonameList.
- IfnextKey
- ReturnnameList.
20.1.2.12 Object.getPrototypeOf (O )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - Return ? obj.[[GetPrototypeOf]]().
20.1.2.13 Object.groupBy (items,callbackfn )
callbackfn should be a function that accepts two arguments.groupBy callscallbackfn once for each element initems, in ascending order, and constructs a new object. Each value returned bycallbackfn is coerced to a
callbackfn is called with two arguments: the value of the element and the index of the element.
The return value ofgroupBy is an object that does not inherit from
This function performs the following steps when called:
- Letgroups be ?
GroupBy (items,callbackfn,property ). - Letobj be
OrdinaryObjectCreate (null ). - For each
Record {[[Key]],[[Elements]] }g ofgroups, do- Letelements be
CreateArrayFromList (g.[[Elements]]). - Perform !
CreateDataPropertyOrThrow (obj,g.[[Key]],elements).
- Letelements be
- Returnobj.
20.1.2.14 Object.hasOwn (O,P )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - Letkey be ?
ToPropertyKey (P). - Return ?
HasOwnProperty (obj,key).
20.1.2.15 Object.is (value1,value2 )
This function performs the following steps when called:
- Return
SameValue (value1,value2).
20.1.2.16 Object.isExtensible (O )
This function performs the following steps when called:
- IfO
is not an Object , returnfalse . - Return ?
IsExtensible (O).
20.1.2.17 Object.isFrozen (O )
This function performs the following steps when called:
- IfO
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,frozen ).
20.1.2.18 Object.isSealed (O )
This function performs the following steps when called:
- IfO
is not an Object , returntrue . - Return ?
TestIntegrityLevel (O,sealed ).
20.1.2.19 Object.keys (O )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - LetkeyList be ?
EnumerableOwnProperties (obj,key ). - Return
CreateArrayFromList (keyList).
20.1.2.20 Object.preventExtensions (O )
This function performs the following steps when called:
- IfO
is not an Object , returnO. - Letstatus be ? O.[[PreventExtensions]]().
- Ifstatus is
false , throw aTypeError exception. - ReturnO.
20.1.2.21 Object.prototype
The initial value ofObject.prototype is the
This property has the attributes {[[Writable]]:
20.1.2.22 Object.seal (O )
This function performs the following steps when called:
- IfO
is not an Object , returnO. - Letstatus be ?
SetIntegrityLevel (O,sealed ). - Ifstatus is
false , throw aTypeError exception. - ReturnO.
20.1.2.23 Object.setPrototypeOf (O,proto )
This function performs the following steps when called:
- SetO to ?
RequireObjectCoercible (O). - Ifproto
is not an Object andproto is notnull , throw aTypeError exception. - IfO
is not an Object , returnO. - Letstatus be ? O.[[SetPrototypeOf]](proto).
- Ifstatus is
false , throw aTypeError exception. - ReturnO.
20.1.2.24 Object.values (O )
This function performs the following steps when called:
- Letobj be ?
ToObject (O). - LetvalueList be ?
EnumerableOwnProperties (obj,value ). - Return
CreateArrayFromList (valueList).
20.1.3 Properties of the Object Prototype Object
TheObject prototype object:
- is%Object.prototype%.
- has an[[Extensible]] internal slot whose value is
true . - has the internal methods defined for
ordinary objects , except for the[[SetPrototypeOf]] method, which is as defined in10.4.7.1 . (Thus, it is animmutable prototype exotic object .) - has a[[Prototype]] internal slot whose value is
null .
20.1.3.1 Object.prototype.constructor
The initial value ofObject.prototype.constructor is
20.1.3.2 Object.prototype.hasOwnProperty (V )
This method performs the following steps when called:
- LetP be ?
ToPropertyKey (V). - LetO be ?
ToObject (this value). - Return ?
HasOwnProperty (O,P).
20.1.3.3 Object.prototype.isPrototypeOf (V )
This method performs the following steps when called:
- IfV
is not an Object , returnfalse . - LetO be ?
ToObject (this value). - Repeat,
- SetV to ? V.[[GetPrototypeOf]]().
- IfV is
null , returnfalse . - If
SameValue (O,V) istrue , returntrue .
20.1.3.4 Object.prototype.propertyIsEnumerable (V )
This method performs the following steps when called:
- LetP be ?
ToPropertyKey (V). - LetO be ?
ToObject (this value). - Letdesc be ? O.[[GetOwnProperty]](P).
- Ifdesc is
undefined , returnfalse . - Returndesc.[[Enumerable]].
This method does not consider objects in the prototype chain.
20.1.3.5 Object.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
This method performs the following steps when called:
- LetO be the
this value. - Return ?
Invoke (O,"toString" ).
The optional parameters to this method are not used but are intended to correspond to the parameter pattern used by ECMA-402toLocaleString methods. Implementations that do not include ECMA-402 support must not use those parameter positions for other purposes.
This method provides a generictoLocaleString implementation for objects that have no locale-sensitivetoString behaviour.Array,Number,Date, andtoLocaleString methods.
ECMA-402 intentionally does not provide an alternative to this default implementation.
20.1.3.6 Object.prototype.toString ( )
This method performs the following steps when called:
- If the
this value isundefined , return"[object Undefined]" . - If the
this value isnull , return"[object Null]" . - LetO be !
ToObject (this value). - LetisArray be ?
IsArray (O). - IfisArray is
true , letbuiltinTag be"Array" . - Else ifO has a[[ParameterMap]] internal slot, letbuiltinTag be
"Arguments" . - Else ifO has a[[Call]] internal method, letbuiltinTag be
"Function" . - Else ifO has an[[ErrorData]] internal slot, letbuiltinTag be
"Error" . - Else ifO has a[[BooleanData]] internal slot, letbuiltinTag be
"Boolean" . - Else ifO has a[[NumberData]] internal slot, letbuiltinTag be
"Number" . - Else ifO has a[[StringData]] internal slot, letbuiltinTag be
"String" . - Else ifO has a[[DateValue]] internal slot, letbuiltinTag be
"Date" . - Else ifO has a[[RegExpMatcher]] internal slot, letbuiltinTag be
"RegExp" . - Else, letbuiltinTag be
"Object" . - Lettag be ?
Get (O,@@toStringTag ). - Iftag
is not a String , settag tobuiltinTag. - Return the
string-concatenation of"[object " ,tag, and"]" .
Historically, this method was occasionally used to access the String value of the[[Class]] internal slot that was used in previous editions of this specification as a nominal type tag for various built-in objects. The above definition oftoString preserves compatibility for legacy code that usestoString as a test for those specific kinds of built-in objects. It does not provide a reliable type testing mechanism for other kinds of built-in or program defined objects. In addition, programs can use
20.1.3.7 Object.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ToObject (this value).
20.1.3.8 Object.prototype.__proto__
Object.prototype.__proto__ is an
20.1.3.8.1 get Object.prototype.__proto__
The value of the[[Get]] attribute is a built-in function that requires no arguments. It performs the following steps when called:
- LetO be ?
ToObject (this value). - Return ? O.[[GetPrototypeOf]]().
20.1.3.8.2 set Object.prototype.__proto__
The value of the[[Set]] attribute is a built-in function that takes an argumentproto. It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Ifproto
is not an Object andproto is notnull , returnundefined . - IfO
is not an Object , returnundefined . - Letstatus be ? O.[[SetPrototypeOf]](proto).
- Ifstatus is
false , throw aTypeError exception. - Return
undefined .
20.1.3.9 Legacy Object.prototype Accessor Methods
20.1.3.9.1 Object.prototype.__defineGetter__ (P,getter )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - If
IsCallable (getter) isfalse , throw aTypeError exception. - Letdesc be PropertyDescriptor {[[Get]]:getter,[[Enumerable]]:
true ,[[Configurable]]:true }. - Letkey be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O,key,desc). - Return
undefined .
20.1.3.9.2 Object.prototype.__defineSetter__ (P,setter )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - If
IsCallable (setter) isfalse , throw aTypeError exception. - Letdesc be PropertyDescriptor {[[Set]]:setter,[[Enumerable]]:
true ,[[Configurable]]:true }. - Letkey be ?
ToPropertyKey (P). - Perform ?
DefinePropertyOrThrow (O,key,desc). - Return
undefined .
20.1.3.9.3 Object.prototype.__lookupGetter__ (P )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letkey be ?
ToPropertyKey (P). - Repeat,
- Letdesc be ? O.[[GetOwnProperty]](key).
- Ifdesc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , returndesc.[[Get]]. - Return
undefined .
- If
- SetO to ? O.[[GetPrototypeOf]]().
- IfO is
null , returnundefined .
20.1.3.9.4 Object.prototype.__lookupSetter__ (P )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letkey be ?
ToPropertyKey (P). - Repeat,
- Letdesc be ? O.[[GetOwnProperty]](key).
- Ifdesc is not
undefined , then- If
IsAccessorDescriptor (desc) istrue , returndesc.[[Set]]. - Return
undefined .
- If
- SetO to ? O.[[GetPrototypeOf]]().
- IfO is
null , returnundefined .
20.1.4 Properties of Object Instances
Object instances have no special properties beyond those inherited from the
20.2 Function Objects
20.2.1 The Function Constructor
The Function
- is%Function%.
- is the initial value of the
"Function" property of theglobal object . - creates and initializes a new
function object when called as a function rather than as aconstructor . Thus the function callFunction(…)is equivalent to the object creation expressionnew Function(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Function behaviour must include asupercall to the Functionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in function behaviour. All ECMAScript syntactic forms for definingfunction objects create instances of Function. There is no syntactic means to create instances of Function subclasses except for the built-in GeneratorFunction, AsyncFunction, and AsyncGeneratorFunction subclasses.
20.2.1.1 Function ( ...parameterArgs,bodyArg )
The last argument (if any) specifies the body (executable code) of a function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- LetC be the
active function object . - IfbodyArg is not present, setbodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,normal ,parameterArgs,bodyArg).
It is permissible but not necessary to have one argument for each formal parameter to be specified. For example, all three of the following expressions produce the same result:
newFunction("a","b","c","return a+b+c")newFunction("a, b, c","return a+b+c")newFunction("a,b","c","return a+b+c")20.2.1.1.1 CreateDynamicFunction (constructor,newTarget,kind,parameterArgs,bodyArg )
The abstract operation CreateDynamicFunction takes argumentsconstructor (anew was initially applied to.parameterArgs andbodyArg reflect the argument values that were passed toconstructor. It performs the following steps when called:
- IfnewTarget is
undefined , setnewTarget toconstructor. - Ifkind is
normal , then- Letprefix be
"function" . - LetexprSym be the grammar symbol
FunctionExpression . - LetbodySym be the grammar symbol
FunctionBody .[~Yield, ~Await] - LetparameterSym be the grammar symbol
FormalParameters .[~Yield, ~Await] - LetfallbackProto be
"%Function.prototype%" .
- Letprefix be
- Else ifkind is
generator , then- Letprefix be
"function*" . - LetexprSym be the grammar symbol
GeneratorExpression . - LetbodySym be the grammar symbol
GeneratorBody . - LetparameterSym be the grammar symbol
FormalParameters .[+Yield, ~Await] - LetfallbackProto be
"%GeneratorFunction.prototype%" .
- Letprefix be
- Else ifkind is
async , then- Letprefix be
"async function" . - LetexprSym be the grammar symbol
AsyncFunctionExpression . - LetbodySym be the grammar symbol
AsyncFunctionBody . - LetparameterSym be the grammar symbol
FormalParameters .[~Yield, +Await] - LetfallbackProto be
"%AsyncFunction.prototype%" .
- Letprefix be
- Else,
Assert :kind isasync-generator .- Letprefix be
"async function*" . - LetexprSym be the grammar symbol
AsyncGeneratorExpression . - LetbodySym be the grammar symbol
AsyncGeneratorBody . - LetparameterSym be the grammar symbol
FormalParameters .[+Yield, +Await] - LetfallbackProto be
"%AsyncGeneratorFunction.prototype%" .
- LetargCount be the number of elements inparameterArgs.
- LetbodyString be ?
ToString (bodyArg). - LetparameterStrings be a new empty
List . - For each elementarg ofparameterArgs, do
- Append ?
ToString (arg) toparameterStrings.
- Append ?
- LetcurrentRealm be
the current Realm Record . - Perform ?
HostEnsureCanCompileStrings (currentRealm,parameterStrings,bodyString,false ). - LetP be the empty String.
- IfargCount > 0, then
- SetP toparameterStrings[0].
- Letk be 1.
- Repeat, whilek <argCount,
- LetnextArgString beparameterStrings[k].
- SetP to the
string-concatenation ofP,"," (a comma), andnextArgString. - Setk tok + 1.
- LetbodyParseString be the
string-concatenation of 0x000A (LINE FEED),bodyString, and 0x000A (LINE FEED). - LetsourceString be the
string-concatenation ofprefix," anonymous(" ,P, 0x000A (LINE FEED),") {" ,bodyParseString, and"}" . - LetsourceText be
StringToCodePoints (sourceString). - Letparameters be
ParseText (StringToCodePoints (P),parameterSym). - Ifparameters is a
List of errors, throw aSyntaxError exception. - Letbody be
ParseText (StringToCodePoints (bodyParseString),bodySym). - Ifbody is a
List of errors, throw aSyntaxError exception. - NOTE: The parameters and body are parsed separately to ensure that each is valid alone. For example,
new Function("/*", "*/ ) {")does not evaluate to a function. - NOTE: If this step is reached,sourceText must have the syntax ofexprSym (although the reverse implication does not hold). The purpose of the next two steps is to enforce any Early Error rules which apply toexprSym directly.
- Letexpr be
ParseText (sourceText,exprSym). - Ifexpr is a
List of errors, throw aSyntaxError exception. - Letproto be ?
GetPrototypeFromConstructor (newTarget,fallbackProto). - Letenv becurrentRealm.[[GlobalEnv]].
- LetprivateEnv be
null . - LetF be
OrdinaryFunctionCreate (proto,sourceText,parameters,body,non-lexical-this ,env,privateEnv). - Perform
SetFunctionName (F,"anonymous" ). - Ifkind is
generator , then- Letprototype be
OrdinaryObjectCreate (%GeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }).
- Letprototype be
- Else ifkind is
async-generator , then- Letprototype be
OrdinaryObjectCreate (%AsyncGeneratorFunction.prototype.prototype% ). - Perform !
DefinePropertyOrThrow (F,"prototype" , PropertyDescriptor {[[Value]]:prototype,[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }).
- Letprototype be
- Else ifkind is
normal , then- Perform
MakeConstructor (F).
- Perform
- NOTE: Functions whosekind is
async are not constructible and do not have a[[Construct]] internal method or a"prototype" property. - ReturnF.
CreateDynamicFunction defines a
20.2.2 Properties of the Function Constructor
The Function
- is itself a built-in
function object . - has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
20.2.2.1 Function.prototype
The value ofFunction.prototype is the
This property has the attributes {[[Writable]]:
20.2.3 Properties of the Function Prototype Object
TheFunction prototype object:
- is%Function.prototype%.
- is itself a built-in
function object . - accepts any arguments and returns
undefined when invoked. - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - has a[[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a
"prototype" property. - has a
"length" property whose value is+0 𝔽. - has a
"name" property whose value is the empty String.
The Function prototype object is specified to be a
20.2.3.1 Function.prototype.apply (thisArg,argArray )
This method performs the following steps when called:
- Letfunc be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - IfargArray is either
undefined ornull , then- Perform
PrepareForTailCall (). - Return ?
Call (func,thisArg).
- Perform
- LetargList be ?
CreateListFromArrayLike (argArray). - Perform
PrepareForTailCall (). - Return ?
Call (func,thisArg,argList).
ThethisArg value is passed without modification as the
Iffunc is either an arrow function or a
20.2.3.2 Function.prototype.bind (thisArg, ...args )
This method performs the following steps when called:
- LetTarget be the
this value. - If
IsCallable (Target) isfalse , throw aTypeError exception. - LetF be ?
BoundFunctionCreate (Target,thisArg,args). - LetL be 0.
- LettargetHasLength be ?
HasOwnProperty (Target,"length" ). - IftargetHasLength is
true , then- LettargetLen be ?
Get (Target,"length" ). - IftargetLen
is a Number , then- IftargetLen is
+∞ 𝔽, then- SetL to +∞.
- Else iftargetLen is
-∞ 𝔽, then- SetL to 0.
- Else,
- LettargetLenAsInt be !
ToIntegerOrInfinity (targetLen). Assert :targetLenAsInt isfinite .- LetargCount be the number of elements inargs.
- SetL to
max (targetLenAsInt -argCount, 0).
- LettargetLenAsInt be !
- IftargetLen is
- LettargetLen be ?
- Perform
SetFunctionLength (F,L). - LettargetName be ?
Get (Target,"name" ). - IftargetName
is not a String , settargetName to the empty String. - Perform
SetFunctionName (F,targetName,"bound" ). - ReturnF.
Function.prototype.bind are
IfTarget is either an arrow function or a
20.2.3.3 Function.prototype.call (thisArg, ...args )
This method performs the following steps when called:
- Letfunc be the
this value. - If
IsCallable (func) isfalse , throw aTypeError exception. - Perform
PrepareForTailCall (). - Return ?
Call (func,thisArg,args).
ThethisArg value is passed without modification as the
Iffunc is either an arrow function or a
20.2.3.4 Function.prototype.constructor
The initial value ofFunction.prototype.constructor is
20.2.3.5 Function.prototype.toString ( )
This method performs the following steps when called:
- Letfunc be the
this value. - Iffunc
is an Object ,func has a[[SourceText]] internal slot,func.[[SourceText]] is a sequence of Unicode code points, andHostHasSourceTextAvailable (func) istrue , then- Return
CodePointsToString (func.[[SourceText]]).
- Return
- Iffunc is a
built-in function object , return animplementation-defined String source code representation offunc. The representation must have the syntax of aNativeFunction . Additionally, iffunc has an[[InitialName]] internal slot andfunc.[[InitialName]]is a String , the portion of the returned String that would be matched byNativeFunctionAccessor opt PropertyName must be the value offunc.[[InitialName]]. - Iffunc
is an Object andIsCallable (func) istrue , return animplementation-defined String source code representation offunc. The representation must have the syntax of aNativeFunction . - Throw a
TypeError exception.
20.2.3.6 Function.prototype [ @@hasInstance ] (V )
This method performs the following steps when called:
- LetF be the
this value. - Return ?
OrdinaryHasInstance (F,V).
This property has the attributes {[[Writable]]:
This is the default implementation of@@hasInstance that most functions inherit.@@hasInstance is called by theinstanceof operator to determine whether a value is an instance of a specific
vinstanceof Fevaluates as
F[@@hasInstance](v)Ainstanceof by exposing a different@@hasInstance method on the function.
This property is non-writable and non-configurable to prevent tampering that could be used to globally expose the target function of a bound function.
The value of the
20.2.4 Function Instances
Every Function instance is an ECMAScriptFunction.prototype.bind method (
Function instances have the following properties:
20.2.4.1 length
The value of the
20.2.4.2 name
The value of the
Anonymous functions objects that do not have a contextual name associated with them by this specification use the empty String as the value of the
20.2.4.3 prototype
Function instances that can be used as a
This property has the attributes {[[Writable]]:
Function.prototype.bind, or by evaluating a
20.2.5 HostHasSourceTextAvailable (func )
The
An implementation of HostHasSourceTextAvailable must conform to the following requirements:
- It must be deterministic with respect to its parameters. Each time it is called with a specificfunc as its argument, it must return the same result.
The default implementation of HostHasSourceTextAvailable is to return
20.3 Boolean Objects
20.3.1 The Boolean Constructor
The Boolean
- is%Boolean%.
- is the initial value of the
"Boolean" property of theglobal object . - creates and initializes a new Boolean object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Boolean behaviour must include asupercall to the Booleanconstructor to create and initialize the subclass instance with a[[BooleanData]] internal slot.
20.3.1.1 Boolean (value )
This function performs the following steps when called:
- Letb be
ToBoolean (value). - If NewTarget is
undefined , returnb. - LetO be ?
OrdinaryCreateFromConstructor (NewTarget,"%Boolean.prototype%" , «[[BooleanData]] »). - SetO.[[BooleanData]] tob.
- ReturnO.
20.3.2 Properties of the Boolean Constructor
The Boolean
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.3.2.1 Boolean.prototype
The initial value ofBoolean.prototype is the
This property has the attributes {[[Writable]]:
20.3.3 Properties of the Boolean Prototype Object
TheBoolean prototype object:
- is%Boolean.prototype%.
- is an
ordinary object . - is itself a Boolean object; it has a[[BooleanData]] internal slot with the value
false . - has a[[Prototype]] internal slot whose value is
%Object.prototype% .
20.3.3.1 Boolean.prototype.constructor
The initial value ofBoolean.prototype.constructor is
20.3.3.2 Boolean.prototype.toString ( )
This method performs the following steps when called:
- Letb be ?
ThisBooleanValue (this value). - Ifb is
true , return"true" ; else return"false" .
20.3.3.3 Boolean.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisBooleanValue (this value).
20.3.3.3.1 ThisBooleanValue (value )
The abstract operation ThisBooleanValue takes argumentvalue (an
- Ifvalue
is a Boolean , returnvalue. - Ifvalue
is an Object andvalue has a[[BooleanData]] internal slot, then- Letb bevalue.[[BooleanData]].
Assert :bis a Boolean .- Returnb.
- Throw a
TypeError exception.
20.3.4 Properties of Boolean Instances
Boolean instances are
20.4 Symbol Objects
20.4.1 The Symbol Constructor
The Symbol
- is%Symbol%.
- is the initial value of the
"Symbol" property of theglobal object . - returns a new Symbol value when called as a function.
- is not intended to be used with the
newoperator. - is not intended to be subclassed.
- may be used as the value of an
extendsclause of a class definition but asupercall to it will cause an exception.
20.4.1.1 Symbol ( [description ] )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - Ifdescription is
undefined , letdescString beundefined . - Else, letdescString be ?
ToString (description). - Return a new Symbol whose[[Description]] isdescString.
20.4.2 Properties of the Symbol Constructor
The Symbol
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.4.2.1 Symbol.asyncIterator
The initial value ofSymbol.asyncIterator is the well known symbol
This property has the attributes {[[Writable]]:
20.4.2.2 Symbol.for (key )
This function performs the following steps when called:
- LetstringKey be ?
ToString (key). - For each elemente of the GlobalSymbolRegistry
List , do- If
SameValue (e.[[Key]],stringKey) istrue , returne.[[Symbol]].
- If
Assert : GlobalSymbolRegistry does not currently contain an entry forstringKey.- LetnewSymbol be a new Symbol whose[[Description]] isstringKey.
- Append the
Record {[[Key]]:stringKey,[[Symbol]]:newSymbol } to the GlobalSymbolRegistryList . - ReturnnewSymbol.
The GlobalSymbolRegistry is an append-only
20.4.2.3 Symbol.hasInstance
The initial value ofSymbol.hasInstance is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.4 Symbol.isConcatSpreadable
The initial value ofSymbol.isConcatSpreadable is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.5 Symbol.iterator
The initial value ofSymbol.iterator is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.6 Symbol.keyFor (sym )
This function performs the following steps when called:
- Ifsym
is not a Symbol , throw aTypeError exception. - Return
KeyForSymbol (sym).
20.4.2.7 Symbol.match
The initial value ofSymbol.match is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.8 Symbol.matchAll
The initial value ofSymbol.matchAll is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.9 Symbol.prototype
The initial value ofSymbol.prototype is the
This property has the attributes {[[Writable]]:
20.4.2.10 Symbol.replace
The initial value ofSymbol.replace is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.11 Symbol.search
The initial value ofSymbol.search is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.12 Symbol.species
The initial value ofSymbol.species is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.13 Symbol.split
The initial value ofSymbol.split is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.14 Symbol.toPrimitive
The initial value ofSymbol.toPrimitive is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.15 Symbol.toStringTag
The initial value ofSymbol.toStringTag is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.2.16 Symbol.unscopables
The initial value ofSymbol.unscopables is the well-known symbol
This property has the attributes {[[Writable]]:
20.4.3 Properties of the Symbol Prototype Object
TheSymbol prototype object:
- is%Symbol.prototype%.
- is an
ordinary object . is not a Symbol instance and does not have a[[SymbolData]] internal slot.- has a[[Prototype]] internal slot whose value is
%Object.prototype% .
20.4.3.1 Symbol.prototype.constructor
The initial value ofSymbol.prototype.constructor is
20.4.3.2 get Symbol.prototype.description
Symbol.prototype.description is an
- Lets be the
this value. - Letsym be ?
ThisSymbolValue (s). - Returnsym.[[Description]].
20.4.3.3 Symbol.prototype.toString ( )
This method performs the following steps when called:
- Letsym be ?
ThisSymbolValue (this value). - Return
SymbolDescriptiveString (sym).
20.4.3.3.1 SymbolDescriptiveString (sym )
The abstract operation SymbolDescriptiveString takes argumentsym (a Symbol) and returns a String. It performs the following steps when called:
- Letdesc besym's[[Description]] value.
- Ifdesc is
undefined , setdesc to the empty String. Assert :descis a String .- Return the
string-concatenation of"Symbol(" ,desc, and")" .
20.4.3.4 Symbol.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
20.4.3.4.1 ThisSymbolValue (value )
The abstract operation ThisSymbolValue takes argumentvalue (an
- Ifvalue
is a Symbol , returnvalue. - Ifvalue
is an Object andvalue has a[[SymbolData]] internal slot, then- Lets bevalue.[[SymbolData]].
Assert :sis a Symbol .- Returns.
- Throw a
TypeError exception.
20.4.3.5 Symbol.prototype [ @@toPrimitive ] (hint )
This method is called by ECMAScript language operators to convert a Symbol object to a primitive value.
It performs the following steps when called:
- Return ?
ThisSymbolValue (this value).
The argument is ignored.
This property has the attributes {[[Writable]]:
The value of the
20.4.3.6 Symbol.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
20.4.4 Properties of Symbol Instances
Symbol instances are
20.4.5 Abstract Operations for Symbols
20.4.5.1 KeyForSymbol (sym )
The abstract operation KeyForSymbol takes argumentsym (a Symbol) and returns a String or
20.5 Error Objects
Instances of Error objects are thrown as exceptions when runtime errors occur. The Error objects may also serve as base objects for user-defined exception classes.
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of theNativeError objects defined in
20.5.1 The Error Constructor
The Error
- is%Error%.
- is the initial value of the
"Error" property of theglobal object . - creates and initializes a new Error object when called as a function rather than as a
constructor . Thus the function callError(…)is equivalent to the object creation expressionnew Error(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Error behaviour must include asupercall to the Errorconstructor to create and initialize subclass instances with an[[ErrorData]] internal slot.
20.5.1.1 Error (message [ ,options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , letnewTarget be theactive function object ; else letnewTarget be NewTarget. - LetO be ?
OrdinaryCreateFromConstructor (newTarget,"%Error.prototype%" , «[[ErrorData]] »). - Ifmessage is not
undefined , then- Letmsg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" ,msg).
- Letmsg be ?
- Perform ?
InstallErrorCause (O,options). - ReturnO.
20.5.2 Properties of the Error Constructor
The Error
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
20.5.2.1 Error.prototype
The initial value ofError.prototype is the
This property has the attributes {[[Writable]]:
20.5.3 Properties of the Error Prototype Object
TheError prototype object:
- is%Error.prototype%.
- is an
ordinary object . - is not an Error instance and does not have an[[ErrorData]] internal slot.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% .
20.5.3.1 Error.prototype.constructor
The initial value ofError.prototype.constructor is
20.5.3.2 Error.prototype.message
The initial value ofError.prototype.message is the empty String.
20.5.3.3 Error.prototype.name
The initial value ofError.prototype.name is
20.5.3.4 Error.prototype.toString ( )
This method performs the following steps when called:
- LetO be the
this value. - IfO
is not an Object , throw aTypeError exception. - Letname be ?
Get (O,"name" ). - Ifname is
undefined , setname to"Error" ; otherwise setname to ?ToString (name). - Letmsg be ?
Get (O,"message" ). - Ifmsg is
undefined , setmsg to the empty String; otherwise setmsg to ?ToString (msg). - Ifname is the empty String, returnmsg.
- Ifmsg is the empty String, returnname.
- Return the
string-concatenation ofname, the code unit 0x003A (COLON), the code unit 0x0020 (SPACE), andmsg.
20.5.4 Properties of Error Instances
Error instances areObject.prototype.toString.
20.5.5 Native Error Types Used in This Standard
A new instance of one of theNativeError objects below or of the AggregateError object is thrown when a runtime error is detected. AllNativeError objects share the same structure, as described in
20.5.5.1 EvalError
The EvalError
This exception is not currently used within this specification. This object remains for compatibility with previous editions of this specification.
20.5.5.2 RangeError
The RangeError
Indicates a value that is not in the set or range of allowable values.
20.5.5.3 ReferenceError
The ReferenceError
Indicate that an invalid reference has been detected.
20.5.5.4 SyntaxError
The SyntaxError
Indicates that a parsing error has occurred.
20.5.5.5 TypeError
The TypeError
TypeError is used to indicate an unsuccessful operation when none of the otherNativeError objects are an appropriate indication of the failure cause.
20.5.5.6 URIError
The URIError
Indicates that one of the global URI handling functions was used in a way that is incompatible with its definition.
20.5.6NativeError Object Structure
When an ECMAScript implementation detects a runtime error, it throws a new instance of one of theNativeError objects defined in
For each error object, references toNativeError in the definition should be replaced with the appropriate error object name from
20.5.6.1 TheNativeError Constructors
EachNativeError
- creates and initializes a newNativeError object when called as a function rather than as a
constructor . A call of the object as a function is equivalent to calling it as aconstructor with the same arguments. Thus the function callNativeError(…)is equivalent to the object creation expressionnewNativeError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedNativeError behaviour must include asupercall to theNativeErrorconstructor to create and initialize subclass instances with an[[ErrorData]] internal slot.
20.5.6.1.1NativeError (message [ ,options ] )
EachNativeError function performs the following steps when called:
- If NewTarget is
undefined , letnewTarget be theactive function object ; else letnewTarget be NewTarget. - LetO be ?
OrdinaryCreateFromConstructor (newTarget,"%NativeError.prototype%", «[[ErrorData]] »). - Ifmessage is not
undefined , then- Letmsg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" ,msg).
- Letmsg be ?
- Perform ?
InstallErrorCause (O,options). - ReturnO.
The actual value of the string passed in step
20.5.6.2 Properties of theNativeError Constructors
EachNativeError
- has a[[Prototype]] internal slot whose value is
%Error% . - has a
"name" property whose value is the String value"NativeError" . - has the following properties:
20.5.6.2.1NativeError.prototype
The initial value ofNativeError.prototype is aNativeError prototype object (
This property has the attributes {[[Writable]]:
20.5.6.3 Properties of theNativeError Prototype Objects
EachNativeError prototype object:
- is an
ordinary object . - is not an Error instance and does not have an[[ErrorData]] internal slot.
- has a[[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.6.3.1NativeError.prototype.constructor
The initial value of the
20.5.6.3.2NativeError.prototype.message
The initial value of the
20.5.6.3.3NativeError.prototype.name
The initial value of the
20.5.6.4 Properties ofNativeError Instances
NativeError instances areObject.prototype.toString (
20.5.7 AggregateError Objects
20.5.7.1 The AggregateError Constructor
The AggregateError
- is%AggregateError%.
- is the initial value of the
"AggregateError" property of theglobal object . - creates and initializes a new AggregateError object when called as a function rather than as a
constructor . Thus the function callAggregateError(…)is equivalent to the object creation expressionnew AggregateError(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AggregateError behaviour must include asupercall to the AggregateErrorconstructor to create and initialize subclass instances with an[[ErrorData]] internal slot.
20.5.7.1.1 AggregateError (errors,message [ ,options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , letnewTarget be theactive function object ; else letnewTarget be NewTarget. - LetO be ?
OrdinaryCreateFromConstructor (newTarget,"%AggregateError.prototype%" , «[[ErrorData]] »). - Ifmessage is not
undefined , then- Letmsg be ?
ToString (message). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"message" ,msg).
- Letmsg be ?
- Perform ?
InstallErrorCause (O,options). - LeterrorsList be ?
IteratorToList (?GetIterator (errors,sync )). - Perform !
DefinePropertyOrThrow (O,"errors" , PropertyDescriptor {[[Configurable]]:true ,[[Enumerable]]:false ,[[Writable]]:true ,[[Value]]:CreateArrayFromList (errorsList) }). - ReturnO.
20.5.7.2 Properties of the AggregateError Constructor
The AggregateError
- has a[[Prototype]] internal slot whose value is
%Error% . - has the following properties:
20.5.7.2.1 AggregateError.prototype
The initial value ofAggregateError.prototype is
This property has the attributes {[[Writable]]:
20.5.7.3 Properties of the AggregateError Prototype Object
TheAggregateError prototype object:
- is%AggregateError.prototype%.
- is an
ordinary object . - is not an Error instance or an AggregateError instance and does not have an[[ErrorData]] internal slot.
- has a[[Prototype]] internal slot whose value is
%Error.prototype% .
20.5.7.3.1 AggregateError.prototype.constructor
The initial value ofAggregateError.prototype.constructor is
20.5.7.3.2 AggregateError.prototype.message
The initial value ofAggregateError.prototype.message is the empty String.
20.5.7.3.3 AggregateError.prototype.name
The initial value ofAggregateError.prototype.name is
20.5.7.4 Properties of AggregateError Instances
AggregateError instances areObject.prototype.toString (
20.5.8 Abstract Operations for Error Objects
20.5.8.1 InstallErrorCause (O,options )
The abstract operation InstallErrorCause takes argumentsO (an Object) andoptions (an
- Ifoptions
is an Object and ?HasProperty (options,"cause" ) istrue , then- Letcause be ?
Get (options,"cause" ). - Perform
CreateNonEnumerableDataPropertyOrThrow (O,"cause" ,cause).
- Letcause be ?
- Return
unused .
21 Numbers and Dates
21.1 Number Objects
21.1.1 The Number Constructor
The Number
- is%Number%.
- is the initial value of the
"Number" property of theglobal object . - creates and initializes a new Number object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Number behaviour must include asupercall to the Numberconstructor to create and initialize the subclass instance with a[[NumberData]] internal slot.
21.1.1.1 Number (value )
This function performs the following steps when called:
- Ifvalue is present, then
- Letprim be ?
ToNumeric (value). - Ifprim
is a BigInt , letn be𝔽 (ℝ (prim)). - Otherwise, letn beprim.
- Letprim be ?
- Else,
- Letn be
+0 𝔽.
- Letn be
- If NewTarget is
undefined , returnn. - LetO be ?
OrdinaryCreateFromConstructor (NewTarget,"%Number.prototype%" , «[[NumberData]] »). - SetO.[[NumberData]] ton.
- ReturnO.
21.1.2 Properties of the Number Constructor
The Number
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.1.2.1 Number.EPSILON
The value ofNumber.EPSILON is the
This property has the attributes {[[Writable]]:
21.1.2.2 Number.isFinite (number )
This function performs the following steps when called:
- Ifnumber
is not a Number , returnfalse . - Ifnumber is not
finite , returnfalse . - Otherwise, return
true .
21.1.2.3 Number.isInteger (number )
This function performs the following steps when called:
- Return
IsIntegralNumber (number).
21.1.2.4 Number.isNaN (number )
This function performs the following steps when called:
- Ifnumber
is not a Number , returnfalse . - Ifnumber is
NaN , returntrue . - Otherwise, return
false .
This function differs from the global isNaN function (
21.1.2.5 Number.isSafeInteger (number )
An
This function performs the following steps when called:
- If
IsIntegralNumber (number) istrue , then - Return
false .
21.1.2.6 Number.MAX_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations ofNumber.MAX_SAFE_INTEGER is shared with at least one other9007199254740992 and9007199254740993 evaluate to the Number value
The value ofNumber.MAX_SAFE_INTEGER is
This property has the attributes {[[Writable]]:
21.1.2.7 Number.MAX_VALUE
The value ofNumber.MAX_VALUE is the largest positive
This property has the attributes {[[Writable]]:
21.1.2.8 Number.MIN_SAFE_INTEGER
Due to rounding behaviour necessitated by precision limitations ofNumber.MIN_SAFE_INTEGER is shared with at least one other-9007199254740992 and-9007199254740993 evaluate to the Number value
The value ofNumber.MIN_SAFE_INTEGER is
This property has the attributes {[[Writable]]:
21.1.2.9 Number.MIN_VALUE
The value ofNumber.MIN_VALUE is the smallest positive value of the
In theNumber.MIN_VALUE must be the smallest non-zero positive value that can actually be represented by the implementation.
This property has the attributes {[[Writable]]:
21.1.2.10 Number.NaN
The value ofNumber.NaN is
This property has the attributes {[[Writable]]:
21.1.2.11 Number.NEGATIVE_INFINITY
The value ofNumber.NEGATIVE_INFINITY is
This property has the attributes {[[Writable]]:
21.1.2.12 Number.parseFloat (string )
The initial value of the
21.1.2.13 Number.parseInt (string,radix )
The initial value of the
21.1.2.14 Number.POSITIVE_INFINITY
The value ofNumber.POSITIVE_INFINITY is
This property has the attributes {[[Writable]]:
21.1.2.15 Number.prototype
The initial value ofNumber.prototype is the
This property has the attributes {[[Writable]]:
21.1.3 Properties of the Number Prototype Object
TheNumber prototype object:
- is%Number.prototype%.
- is an
ordinary object . - is itself a Number object; it has a[[NumberData]] internal slot with the value
+0 𝔽. - has a[[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the Number prototype object defined below are not generic and the
The phrase “this Number value” within the specification of a method refers to the result returned by calling the abstract operation
21.1.3.1 Number.prototype.constructor
The initial value ofNumber.prototype.constructor is
21.1.3.2 Number.prototype.toExponential (fractionDigits )
This method returns a String containing this Number value represented in decimal exponential notation with one digit before the significand's decimal point andfractionDigits digits after the significand's decimal point. IffractionDigits is
It performs the following steps when called:
- Letx be ?
ThisNumberValue (this value). - Letf be ?
ToIntegerOrInfinity (fractionDigits). Assert : IffractionDigits isundefined , thenf is 0.- Ifx is not
finite , returnNumber::toString (x, 10). - Iff < 0 orf > 100, throw a
RangeError exception. - Setx to
ℝ (x). - Lets be the empty String.
- Ifx < 0, then
- Sets to
"-" . - Setx to -x.
- Sets to
- Ifx = 0, then
- Letm be the String value consisting off + 1 occurrences of the code unit 0x0030 (DIGIT ZERO).
- Lete be 0.
- Else,
- IffractionDigits is not
undefined , then- Lete andn be
integers such that 10f ≤n < 10f + 1 and for whichn × 10e -f -x is as close to zero as possible. If there are two such sets ofe andn, pick thee andn for whichn × 10e -f is larger.
- Lete andn be
- Else,
- Lete,n, andff be
integers such thatff ≥ 0, 10ff ≤n < 10ff + 1,𝔽 (n × 10e -ff) is𝔽 (x), andff is as small as possible. Note that the decimal representation ofn hasff + 1 digits,n is not divisible by 10, and the least significant digit ofn is not necessarily uniquely determined by these criteria. - Setf toff.
- Lete,n, andff be
- Letm be the String value consisting of the digits of the decimal representation ofn (in order, with no leading zeroes).
- IffractionDigits is not
- Iff ≠ 0, then
- Leta be the first code unit ofm.
- Letb be the otherf code units ofm.
- Setm to the
string-concatenation ofa,"." , andb.
- Ife = 0, then
- Letc be
"+" . - Letd be
"0" .
- Letc be
- Else,
- Ife > 0, then
- Letc be
"+" .
- Letc be
- Else,
Assert :e < 0.- Letc be
"-" . - Sete to -e.
- Letd be the String value consisting of the digits of the decimal representation ofe (in order, with no leading zeroes).
- Ife > 0, then
- Setm to the
string-concatenation ofm,"e" ,c, andd. - Return the
string-concatenation ofs andm.
For implementations that provide more accurate conversions than required by the rules above, it is recommended that the following alternative version of step
21.1.3.3 Number.prototype.toFixed (fractionDigits )
This method returns a String containing this Number value represented in decimal fixed-point notation withfractionDigits digits after the decimal point. IffractionDigits is
It performs the following steps when called:
- Letx be ?
ThisNumberValue (this value). - Letf be ?
ToIntegerOrInfinity (fractionDigits). Assert : IffractionDigits isundefined , thenf is 0.- Iff is not
finite , throw aRangeError exception. - Iff < 0 orf > 100, throw a
RangeError exception. - Ifx is not
finite , returnNumber::toString (x, 10). - Setx to
ℝ (x). - Lets be the empty String.
- Ifx < 0, then
- Sets to
"-" . - Setx to -x.
- Sets to
- Ifx ≥ 1021, then
- Else,
- Letn be an
integer for whichn / 10f -x is as close to zero as possible. If there are two suchn, pick the largern. - Ifn = 0, letm be
"0" . Otherwise, letm be the String value consisting of the digits of the decimal representation ofn (in order, with no leading zeroes). - Iff ≠ 0, then
- Letk be the length ofm.
- Ifk ≤f, then
- Letz be the String value consisting off + 1 -k occurrences of the code unit 0x0030 (DIGIT ZERO).
- Setm to the
string-concatenation ofz andm. - Setk tof + 1.
- Leta be the firstk -f code units ofm.
- Letb be the otherf code units ofm.
- Setm to the
string-concatenation ofa,"." , andb.
- Letn be an
- Return the
string-concatenation ofs andm.
The output oftoFixed may be more precise thantoString for some values because toString only prints enough significant digits to distinguish the number from adjacent Number values. For example,
(1000000000000000128).toString() returns(1000000000000000128).toFixed(0) returns
21.1.3.4 Number.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this Number value formatted according to the conventions of thetoString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.1.3.5 Number.prototype.toPrecision (precision )
This method returns a String containing this Number value represented either in decimal exponential notation with one digit before the significand's decimal point and
It performs the following steps when called:
- Letx be ?
ThisNumberValue (this value). - Ifprecision is
undefined , return !ToString (x). - Letp be ?
ToIntegerOrInfinity (precision). - Ifx is not
finite , returnNumber::toString (x, 10). - Ifp < 1 orp > 100, throw a
RangeError exception. - Setx to
ℝ (x). - Lets be the empty String.
- Ifx < 0, then
- Sets to the code unit 0x002D (HYPHEN-MINUS).
- Setx to -x.
- Ifx = 0, then
- Letm be the String value consisting ofp occurrences of the code unit 0x0030 (DIGIT ZERO).
- Lete be 0.
- Else,
- Lete andn be
integers such that 10p - 1 ≤n < 10p and for whichn × 10e -p + 1 -x is as close to zero as possible. If there are two such sets ofe andn, pick thee andn for whichn × 10e -p + 1 is larger. - Letm be the String value consisting of the digits of the decimal representation ofn (in order, with no leading zeroes).
- Ife < -6 ore ≥p, then
Assert :e ≠ 0.- Ifp ≠ 1, then
- Leta be the first code unit ofm.
- Letb be the otherp - 1 code units ofm.
- Setm to the
string-concatenation ofa,"." , andb.
- Ife > 0, then
- Letc be the code unit 0x002B (PLUS SIGN).
- Else,
Assert :e < 0.- Letc be the code unit 0x002D (HYPHEN-MINUS).
- Sete to -e.
- Letd be the String value consisting of the digits of the decimal representation ofe (in order, with no leading zeroes).
- Return the
string-concatenation ofs,m, the code unit 0x0065 (LATIN SMALL LETTER E),c, andd.
- Lete andn be
- Ife =p - 1, return the
string-concatenation ofs andm. - Ife ≥ 0, then
- Setm to the
string-concatenation of the firste + 1 code units ofm, the code unit 0x002E (FULL STOP), and the remainingp - (e + 1) code units ofm.
- Setm to the
- Else,
- Setm to the
string-concatenation of the code unit 0x0030 (DIGIT ZERO), the code unit 0x002E (FULL STOP), -(e + 1) occurrences of the code unit 0x0030 (DIGIT ZERO), and the Stringm.
- Setm to the
- Return the
string-concatenation ofs andm.
21.1.3.6 Number.prototype.toString ( [radix ] )
The optionalradix should be an
This method performs the following steps when called:
- Letx be ?
ThisNumberValue (this value). - Ifradix is
undefined , letradixMV be 10. - Else, letradixMV be ?
ToIntegerOrInfinity (radix). - IfradixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
Number::toString (x,radixMV).
This method is not generic; it throws a
The
21.1.3.7 Number.prototype.valueOf ( )
- Return ?
ThisNumberValue (this value).
21.1.3.7.1 ThisNumberValue (value )
The abstract operation ThisNumberValue takes argumentvalue (an
- Ifvalue
is a Number , returnvalue. - Ifvalue
is an Object andvalue has a[[NumberData]] internal slot, then- Letn bevalue.[[NumberData]].
Assert :nis a Number .- Returnn.
- Throw a
TypeError exception.
21.1.4 Properties of Number Instances
Number instances are
21.2 BigInt Objects
21.2.1 The BigInt Constructor
The BigInt
- is%BigInt%.
- is the initial value of the
"BigInt" property of theglobal object . - performs a type conversion when called as a function rather than as a
constructor . - is not intended to be used with the
newoperator or to be subclassed. It may be used as the value of anextendsclause of a class definition but asupercall to the BigIntconstructor will cause an exception.
21.2.1.1 BigInt (value )
This function performs the following steps when called:
- If NewTarget is not
undefined , throw aTypeError exception. - Letprim be ?
ToPrimitive (value,number ). - Ifprim
is a Number , return ?NumberToBigInt (prim). - Otherwise, return ?
ToBigInt (prim).
21.2.1.1.1 NumberToBigInt (number )
The abstract operation NumberToBigInt takes argumentnumber (a Number) and returns either a
- If
IsIntegralNumber (number) isfalse , throw aRangeError exception. - Return
ℤ (ℝ (number)).
21.2.2 Properties of the BigInt Constructor
The BigInt
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
21.2.2.1 BigInt.asIntN (bits,bigint )
This function performs the following steps when called:
21.2.2.2 BigInt.asUintN (bits,bigint )
This function performs the following steps when called:
21.2.2.3 BigInt.prototype
The initial value ofBigInt.prototype is the
This property has the attributes {[[Writable]]:
21.2.3 Properties of the BigInt Prototype Object
TheBigInt prototype object:
- is%BigInt.prototype%.
- is an
ordinary object . is not a BigInt object; it does not have a[[BigIntData]] internal slot.- has a[[Prototype]] internal slot whose value is
%Object.prototype% .
The phrase “this BigInt value” within the specification of a method refers to the result returned by calling the abstract operation
21.2.3.1 BigInt.prototype.constructor
The initial value ofBigInt.prototype.constructor is
21.2.3.2 BigInt.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method produces a String value that represents this BigInt value formatted according to the conventions of thetoString.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.2.3.3 BigInt.prototype.toString ( [radix ] )
The optionalradix should be an
This method performs the following steps when called:
- Letx be ?
ThisBigIntValue (this value). - Ifradix is
undefined , letradixMV be 10. - Else, letradixMV be ?
ToIntegerOrInfinity (radix). - IfradixMV is not in the
inclusive interval from 2 to 36, throw aRangeError exception. - Return
BigInt::toString (x,radixMV).
This method is not generic; it throws a
21.2.3.4 BigInt.prototype.valueOf ( )
- Return ?
ThisBigIntValue (this value).
21.2.3.4.1 ThisBigIntValue (value )
The abstract operation ThisBigIntValue takes argumentvalue (an
- Ifvalue
is a BigInt , returnvalue. - Ifvalue
is an Object andvalue has a[[BigIntData]] internal slot, thenAssert :value.[[BigIntData]]is a BigInt .- Returnvalue.[[BigIntData]].
- Throw a
TypeError exception.
21.2.3.5 BigInt.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
21.2.4 Properties of BigInt Instances
BigInt instances are
21.3 The Math Object
The Math object:
- is%Math%.
- is the initial value of the
"Math" property of theglobal object . - is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a[[Call]] internal method; it cannot be invoked as a function.
In this specification, the phrase “the
21.3.1 Value Properties of the Math Object
21.3.1.1 Math.E
The
This property has the attributes {[[Writable]]:
21.3.1.2 Math.LN10
The
This property has the attributes {[[Writable]]:
21.3.1.3 Math.LN2
The
This property has the attributes {[[Writable]]:
21.3.1.4 Math.LOG10E
The
This property has the attributes {[[Writable]]:
The value ofMath.LOG10E is approximately the reciprocal of the value ofMath.LN10.
21.3.1.5 Math.LOG2E
The
This property has the attributes {[[Writable]]:
The value ofMath.LOG2E is approximately the reciprocal of the value ofMath.LN2.
21.3.1.6 Math.PI
The
This property has the attributes {[[Writable]]:
21.3.1.7 Math.SQRT1_2
The
This property has the attributes {[[Writable]]:
The value ofMath.SQRT1_2 is approximately the reciprocal of the value ofMath.SQRT2.
21.3.1.8 Math.SQRT2
The
This property has the attributes {[[Writable]]:
21.3.1.9 Math [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
21.3.2 Function Properties of the Math Object
The behaviour of the functionsacos,acosh,asin,asinh,atan,atanh,atan2,cbrt,cos,cosh,exp,expm1,hypot,log,log1p,log2,log10,pow,random,sin,sinh,sqrt,tan, andtanh is not precisely specified here except to require specific results for certain argument values that represent boundary cases of interest. For other argument values, these functions are intended to compute approximations to the results of familiar mathematical functions, but some latitude is allowed in the choice of approximation algorithms. The general intent is that an implementer should be able to use the same mathematical library for ECMAScript on a given hardware platform that is available to C programmers on that platform.
Although the choice of algorithms is left to the implementation, it is recommended (but not specified by this standard) that implementations use the approximation algorithms forfdlibm, the freely distributable mathematical library from Sun Microsystems (http://www.netlib.org/fdlibm).
21.3.2.1 Math.abs (x )
This function returns the absolute value ofx; the result has the same magnitude asx but has positive sign.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is
NaN , returnNaN . - Ifn is
-0 𝔽, return+0 𝔽. - Ifn is
-∞ 𝔽, return+∞ 𝔽. - Ifn <
-0 𝔽, return -n. - Returnn.
21.3.2.2 Math.acos (x )
This function returns the inverse cosine ofx. The result is expressed in radians and is in the
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is
NaN ,n >1 𝔽, orn <-1 𝔽, returnNaN . - Ifn is
1 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the result of the inverse cosine ofℝ (n).
21.3.2.3 Math.acosh (x )
This function returns the inverse hyperbolic cosine ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is either
NaN or+∞ 𝔽, returnn. - Ifn is
1 𝔽, return+0 𝔽. - Ifn <
1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic cosine ofℝ (n).
21.3.2.4 Math.asin (x )
This function returns the inverse sine ofx. The result is expressed in radians and is in the
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn >
1 𝔽 orn <-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the inverse sine ofℝ (n).
21.3.2.5 Math.asinh (x )
This function returns the inverse hyperbolic sine ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic sine ofℝ (n).
21.3.2.6 Math.atan (x )
This function returns the inverse tangent ofx. The result is expressed in radians and is in the
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn is
+∞ 𝔽, return animplementation-approximated Number value representing π / 2. - Ifn is
-∞ 𝔽, return animplementation-approximated Number value representing -π / 2. - Return an
implementation-approximated Number value representing the result of the inverse tangent ofℝ (n).
21.3.2.7 Math.atanh (x )
This function returns the inverse hyperbolic tangent ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn >
1 𝔽 orn <-1 𝔽, returnNaN . - Ifn is
1 𝔽, return+∞ 𝔽. - Ifn is
-1 𝔽, return-∞ 𝔽. - Return an
implementation-approximated Number value representing the result of the inverse hyperbolic tangent ofℝ (n).
21.3.2.8 Math.atan2 (y,x )
This function returns the inverse tangent of the quotient
It performs the following steps when called:
- Letny be ?
ToNumber (y). - Letnx be ?
ToNumber (x). - Ifny is
NaN ornx isNaN , returnNaN . - Ifny is
+∞ 𝔽, then- Ifnx is
+∞ 𝔽, return animplementation-approximated Number value representing π / 4. - Ifnx is
-∞ 𝔽, return animplementation-approximated Number value representing 3π / 4. - Return an
implementation-approximated Number value representing π / 2.
- Ifnx is
- Ifny is
-∞ 𝔽, then- Ifnx is
+∞ 𝔽, return animplementation-approximated Number value representing -π / 4. - Ifnx is
-∞ 𝔽, return animplementation-approximated Number value representing -3π / 4. - Return an
implementation-approximated Number value representing -π / 2.
- Ifnx is
- Ifny is
+0 𝔽, then- Ifnx >
+0 𝔽 ornx is+0 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing π.
- Ifnx >
- Ifny is
-0 𝔽, then- Ifnx >
+0 𝔽 ornx is+0 𝔽, return-0 𝔽. - Return an
implementation-approximated Number value representing -π.
- Ifnx >
Assert :ny isfinite and is neither+0 𝔽 nor-0 𝔽.- Ifny >
+0 𝔽, then- Ifnx is
+∞ 𝔽, return+0 𝔽. - Ifnx is
-∞ 𝔽, return animplementation-approximated Number value representing π. - Ifnx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing π / 2.
- Ifnx is
- Ifny <
-0 𝔽, then- Ifnx is
+∞ 𝔽, return-0 𝔽. - Ifnx is
-∞ 𝔽, return animplementation-approximated Number value representing -π. - Ifnx is either
+0 𝔽 or-0 𝔽, return animplementation-approximated Number value representing -π / 2.
- Ifnx is
Assert :nx isfinite and is neither+0 𝔽 nor-0 𝔽.- Letr be the inverse tangent of
abs (ℝ (ny) /ℝ (nx)). - Ifnx <
-0 𝔽, then- Ifny >
+0 𝔽, setr to π -r. - Else, setr to -π +r.
- Ifny >
- Else,
- Ifny <
-0 𝔽, setr to -r.
- Ifny <
- Return an
implementation-approximated Number value representingr.
21.3.2.9 Math.cbrt (x )
This function returns the cube root ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Return an
implementation-approximated Number value representing the result of the cube root ofℝ (n).
21.3.2.10 Math.ceil (x )
This function returns the smallest (closest to -∞)
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Ifn <
-0 𝔽 andn >-1 𝔽, return-0 𝔽. - Ifn is an
integral Number , returnn. - Return the smallest (closest to -∞)
integral Number value that is not less thann.
The value ofMath.ceil(x) is the same as the value of-Math.floor(-x).
21.3.2.11 Math.clz32 (x )
This function performs the following steps when called:
Ifn is either
21.3.2.12 Math.cos (x )
This function returns the cosine ofx. The argument is expressed in radians.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite , returnNaN . - Ifn is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the result of the cosine ofℝ (n).
21.3.2.13 Math.cosh (x )
This function returns the hyperbolic cosine ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is
NaN , returnNaN . - Ifn is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽. - Ifn is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Return an
implementation-approximated Number value representing the result of the hyperbolic cosine ofℝ (n).
The value ofMath.cosh(x) is the same as the value of(Math.exp(x) + Math.exp(-x)) / 2.
21.3.2.14 Math.exp (x )
This function returns the exponential function ofx (e raised to the power ofx, wheree is the base of the natural logarithms).
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is either
NaN or+∞ 𝔽, returnn. - Ifn is either
+0 𝔽 or-0 𝔽, return1 𝔽. - Ifn is
-∞ 𝔽, return+0 𝔽. - Return an
implementation-approximated Number value representing the result of the exponential function ofℝ (n).
21.3.2.15 Math.expm1 (x )
This function returns the result of subtracting 1 from the exponential function ofx (e raised to the power ofx, wheree is the base of the natural logarithms). The result is computed in a way that is accurate even when the value ofx is close to 0.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, returnn. - Ifn is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the result of subtracting 1 from the exponential function ofℝ (n).
21.3.2.16 Math.floor (x )
This function returns the greatest (closest to +∞)
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Ifn <
1 𝔽 andn >+0 𝔽, return+0 𝔽. - Ifn is an
integral Number , returnn. - Return the greatest (closest to +∞)
integral Number value that is not greater thann.
The value ofMath.floor(x) is the same as the value of-Math.ceil(-x).
21.3.2.17 Math.fround (x )
This function performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is
NaN , returnNaN . - Ifn is one of
+0 𝔽,-0 𝔽,+∞ 𝔽, or-∞ 𝔽, returnn. - Letn32 be the result of convertingn to
IEEE 754-2019 binary32 format using roundTiesToEven mode. - Letn64 be the result of convertingn32 to
IEEE 754-2019 binary64 format. - Return the ECMAScript Number value corresponding ton64.
21.3.2.18 Math.hypot ( ...args )
Given zero or more arguments, this function returns the square root of the sum of squares of its arguments.
It performs the following steps when called:
- Letcoerced be a new empty
List . - For each elementarg ofargs, do
- Letn be ?
ToNumber (arg). - Appendn tocoerced.
- Letn be ?
- For each elementnumber ofcoerced, do
- Ifnumber is either
+∞ 𝔽 or-∞ 𝔽, return+∞ 𝔽.
- Ifnumber is either
- LetonlyZero be
true . - For each elementnumber ofcoerced, do
- Ifnumber is
NaN , returnNaN . - Ifnumber is neither
+0 𝔽 nor-0 𝔽, setonlyZero tofalse .
- Ifnumber is
- IfonlyZero is
true , return+0 𝔽. - Return an
implementation-approximated Number value representing the square root of the sum of squares of themathematical values of the elements ofcoerced.
The
Implementations should take care to avoid the loss of precision from overflows and underflows that are prone to occur in naive implementations when this function is called with two or more arguments.
21.3.2.19 Math.imul (x,y )
This function performs the following steps when called:
21.3.2.20 Math.log (x )
This function returns the natural logarithm ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is either
NaN or+∞ 𝔽, returnn. - Ifn is
1 𝔽, return+0 𝔽. - Ifn is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - Ifn <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the natural logarithm ofℝ (n).
21.3.2.21 Math.log1p (x )
This function returns the natural logarithm of 1 +x. The result is computed in a way that is accurate even when the value of x is close to zero.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, returnn. - Ifn is
-1 𝔽, return-∞ 𝔽. - Ifn <
-1 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the natural logarithm of 1 +ℝ (n).
21.3.2.22 Math.log10 (x )
This function returns the base 10 logarithm ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is either
NaN or+∞ 𝔽, returnn. - Ifn is
1 𝔽, return+0 𝔽. - Ifn is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - Ifn <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the base 10 logarithm ofℝ (n).
21.3.2.23 Math.log2 (x )
This function returns the base 2 logarithm ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is either
NaN or+∞ 𝔽, returnn. - Ifn is
1 𝔽, return+0 𝔽. - Ifn is either
+0 𝔽 or-0 𝔽, return-∞ 𝔽. - Ifn <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the base 2 logarithm ofℝ (n).
21.3.2.24 Math.max ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
The comparison of values to determine the largest value is done using the
The
21.3.2.25 Math.min ( ...args )
Given zero or more arguments, this function calls
It performs the following steps when called:
The comparison of values to determine the largest value is done using the
The
21.3.2.26 Math.pow (base,exponent )
This function performs the following steps when called:
- Setbase to ?
ToNumber (base). - Setexponent to ?
ToNumber (exponent). - Return
Number::exponentiate (base,exponent).
21.3.2.27 Math.random ( )
This function returns a Number value with positive sign, greater than or equal to
EachMath.random function created for distinct
21.3.2.28 Math.round (x )
This function returns the Number value that is closest tox and is integral. If two
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is anintegral Number , returnn. - Ifn <
0.5 𝔽 andn >+0 𝔽, return+0 𝔽. - Ifn <
-0 𝔽 andn ≥-0.5 𝔽, return-0 𝔽. - Return the
integral Number closest ton, preferring the Number closer to +∞ in the case of a tie.
Math.round(3.5) returns 4, butMath.round(-3.5) returns -3.
The value ofMath.round(x) is not always the same as the value ofMath.floor(x + 0.5). Whenx isx is less thanMath.round(x) returnsMath.floor(x + 0.5) returnsMath.round(x) may also differ from the value ofMath.floor(x + 0.5)because of internal rounding when computingx + 0.5.
21.3.2.29 Math.sign (x )
This function returns the sign ofx, indicating whetherx is positive, negative, or zero.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn <
-0 𝔽, return-1 𝔽. - Return
1 𝔽.
21.3.2.30 Math.sin (x )
This function returns the sine ofx. The argument is expressed in radians.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the sine ofℝ (n).
21.3.2.31 Math.sinh (x )
This function returns the hyperbolic sine ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Return an
implementation-approximated Number value representing the result of the hyperbolic sine ofℝ (n).
The value ofMath.sinh(x) is the same as the value of(Math.exp(x) - Math.exp(-x)) / 2.
21.3.2.32 Math.sqrt (x )
This function returns the square root ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽,-0 𝔽, or+∞ 𝔽, returnn. - Ifn <
-0 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the square root ofℝ (n).
21.3.2.33 Math.tan (x )
This function returns the tangent ofx. The argument is expressed in radians.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn is either
+∞ 𝔽 or-∞ 𝔽, returnNaN . - Return an
implementation-approximated Number value representing the result of the tangent ofℝ (n).
21.3.2.34 Math.tanh (x )
This function returns the hyperbolic tangent ofx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is one of
NaN ,+0 𝔽, or-0 𝔽, returnn. - Ifn is
+∞ 𝔽, return1 𝔽. - Ifn is
-∞ 𝔽, return-1 𝔽. - Return an
implementation-approximated Number value representing the result of the hyperbolic tangent ofℝ (n).
The value ofMath.tanh(x) is the same as the value of(Math.exp(x) - Math.exp(-x)) / (Math.exp(x) + Math.exp(-x)).
21.3.2.35 Math.trunc (x )
This function returns the integral part of the numberx, removing any fractional digits. Ifx is already integral, the result isx.
It performs the following steps when called:
- Letn be ?
ToNumber (x). - Ifn is not
finite orn is either+0 𝔽 or-0 𝔽, returnn. - Ifn <
1 𝔽 andn >+0 𝔽, return+0 𝔽. - Ifn <
-0 𝔽 andn >-1 𝔽, return-0 𝔽. - Return the
integral Number nearestn in the direction of+0 𝔽.
21.4 Date Objects
21.4.1 Overview of Date Objects and Definitions of Abstract Operations
The following
21.4.1.1 Time Values and Time Range
Time measurement in ECMAScript is analogous to time measurement in POSIX, in particular sharing definition in terms of the proleptic Gregorian calendar, anepoch of midnight at the beginning of 1 January 1970 UTC, and an accounting of every day as comprising exactly 86,400 seconds (each of which is 1000 milliseconds long).
An ECMAScripttime value
Time values do not account for UTC leap seconds—there are no time values representing instants within positive leap seconds, and there are time values representing instants removed from the UTC timeline by negative leap seconds. However, the definition of time values nonetheless yields piecewise alignment with UTC, with discontinuities only at leap second boundaries and zero difference outside of leap seconds.
A Number can exactly represent all
The exact moment of midnight at the beginning of 1 January 1970 UTC is represented by the time value
In the proleptic Gregorian calendar, leap years are precisely those which are both divisible by 4 and either divisible by 400 or not divisible by 100.
The 400 year cycle of the proleptic Gregorian calendar contains 97 leap years. This yields an average of 365.2425 days per year, which is 31,556,952,000 milliseconds. Therefore, the maximum range a Number could represent exactly with millisecond precision is approximately -285,426 to 285,426 years relative to 1970. The smaller range supported by a time value as specified in this section is approximately -273,790 to 273,790 years relative to 1970.
21.4.1.2 Time-related Constants
These constants are referenced by algorithms in the following sections.
21.4.1.3 Day (t )
The abstract operation Day takes argumentt (a
21.4.1.4 TimeWithinDay (t )
The abstract operation TimeWithinDay takes argumentt (a
21.4.1.5 DaysInYear (y )
The abstract operation DaysInYear takes argumenty (an
21.4.1.6 DayFromYear (y )
The abstract operation DayFromYear takes argumenty (an
- Letry be
ℝ (y). - NOTE: In the following steps,numYears1,numYears4,numYears100, andnumYears400 represent the number of years divisible by 1, 4, 100, and 400, respectively, that occur between the
epoch and the start of yeary. The number is negative ify is before theepoch . - LetnumYears1 be (ry - 1970).
- LetnumYears4 be
floor ((ry - 1969) / 4). - LetnumYears100 be
floor ((ry - 1901) / 100). - LetnumYears400 be
floor ((ry - 1601) / 400). - Return
𝔽 (365 ×numYears1 +numYears4 -numYears100 +numYears400).
21.4.1.7 TimeFromYear (y )
The abstract operation TimeFromYear takes argumenty (an
- Return
msPerDay ×DayFromYear (y).
21.4.1.8 YearFromTime (t )
The abstract operation YearFromTime takes argumentt (a
- Return the largest
integral Number y (closest to +∞) such thatTimeFromYear (y) ≤t.
21.4.1.9 DayWithinYear (t )
The abstract operation DayWithinYear takes argumentt (a
- Return
Day (t) -DayFromYear (YearFromTime (t)).
21.4.1.10 InLeapYear (t )
The abstract operation InLeapYear takes argumentt (a
- If
DaysInYear (YearFromTime (t)) is366 𝔽, return1 𝔽; else return+0 𝔽.
21.4.1.11 MonthFromTime (t )
The abstract operation MonthFromTime takes argumentt (a
- LetinLeapYear be
InLeapYear (t). - LetdayWithinYear be
DayWithinYear (t). - IfdayWithinYear <
31 𝔽, return+0 𝔽. - IfdayWithinYear <
59 𝔽 +inLeapYear, return1 𝔽. - IfdayWithinYear <
90 𝔽 +inLeapYear, return2 𝔽. - IfdayWithinYear <
120 𝔽 +inLeapYear, return3 𝔽. - IfdayWithinYear <
151 𝔽 +inLeapYear, return4 𝔽. - IfdayWithinYear <
181 𝔽 +inLeapYear, return5 𝔽. - IfdayWithinYear <
212 𝔽 +inLeapYear, return6 𝔽. - IfdayWithinYear <
243 𝔽 +inLeapYear, return7 𝔽. - IfdayWithinYear <
273 𝔽 +inLeapYear, return8 𝔽. - IfdayWithinYear <
304 𝔽 +inLeapYear, return9 𝔽. - IfdayWithinYear <
334 𝔽 +inLeapYear, return10 𝔽. Assert :dayWithinYear <365 𝔽 +inLeapYear.- Return
11 𝔽.
21.4.1.12 DateFromTime (t )
The abstract operation DateFromTime takes argumentt (a
- LetinLeapYear be
InLeapYear (t). - LetdayWithinYear be
DayWithinYear (t). - Letmonth be
MonthFromTime (t). - Ifmonth is
+0 𝔽, returndayWithinYear +1 𝔽. - Ifmonth is
1 𝔽, returndayWithinYear -30 𝔽. - Ifmonth is
2 𝔽, returndayWithinYear -58 𝔽 -inLeapYear. - Ifmonth is
3 𝔽, returndayWithinYear -89 𝔽 -inLeapYear. - Ifmonth is
4 𝔽, returndayWithinYear -119 𝔽 -inLeapYear. - Ifmonth is
5 𝔽, returndayWithinYear -150 𝔽 -inLeapYear. - Ifmonth is
6 𝔽, returndayWithinYear -180 𝔽 -inLeapYear. - Ifmonth is
7 𝔽, returndayWithinYear -211 𝔽 -inLeapYear. - Ifmonth is
8 𝔽, returndayWithinYear -242 𝔽 -inLeapYear. - Ifmonth is
9 𝔽, returndayWithinYear -272 𝔽 -inLeapYear. - Ifmonth is
10 𝔽, returndayWithinYear -303 𝔽 -inLeapYear. Assert :month is11 𝔽.- ReturndayWithinYear -
333 𝔽 -inLeapYear.
21.4.1.13 WeekDay (t )
The abstract operation WeekDay takes argumentt (a
21.4.1.14 HourFromTime (t )
The abstract operation HourFromTime takes argumentt (a
21.4.1.15 MinFromTime (t )
The abstract operation MinFromTime takes argumentt (a
- Return
𝔽 (floor (ℝ (t /msPerMinute ))modulo MinutesPerHour ).
21.4.1.16 SecFromTime (t )
The abstract operation SecFromTime takes argumentt (a
- Return
𝔽 (floor (ℝ (t /msPerSecond ))modulo SecondsPerMinute ).
21.4.1.17 msFromTime (t )
The abstract operation msFromTime takes argumentt (a
- Return
𝔽 (ℝ (t)modulo ℝ (msPerSecond )).
21.4.1.18 GetUTCEpochNanoseconds (year,month,day,hour,minute,second,millisecond,microsecond,nanosecond )
The abstract operation GetUTCEpochNanoseconds takes argumentsyear (an
21.4.1.19 Time Zone Identifiers
Time zones in ECMAScript are represented bytime zone identifiers, which are Strings composed entirely of code units in the
Aprimary time zone identifier is the preferred identifier for an available named time zone. Anon-primary time zone identifier is an identifier for an available named time zone that is not a primary time zone identifier. Anavailable named time zone identifier is either a primary time zone identifier or a non-primary time zone identifier. Each available named time zone identifier is associated with exactly one available named time zone. Each available named time zone is associated with exactly one primary time zone identifier and zero or more non-primary time zone identifiers.
ECMAScript implementations must support an available named time zone with the identifier
Implementations that follow the requirements for time zones as described in the ECMA-402 Internationalization API specification are calledtime zone aware. Time zone aware implementations must support available named time zones corresponding to the Zone and Link names of the IANA Time Zone Database, and only such names. In time zone aware implementations, a primary time zone identifier is a Zone name, and a non-primary time zone identifier is a Link name, respectively, in the IANA Time Zone Database except as specifically overridden by
21.4.1.20 GetNamedTimeZoneEpochNanoseconds (timeZoneIdentifier,year,month,day,hour,minute,second,millisecond,microsecond,nanosecond )
The
When the input represents a local time occurring more than once because of a negative time zone transition (e.g. when daylight saving time ends or the time zone offset is decreased due to a time zone rule change), the returned
The default implementation of GetNamedTimeZoneEpochNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert :timeZoneIdentifier is"UTC" .- LetepochNanoseconds be
GetUTCEpochNanoseconds (year,month,day,hour,minute,second,millisecond,microsecond,nanosecond). - Return «epochNanoseconds ».
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice, so GetNamedTimeZoneEpochNanoseconds(
2:30 AM on 12 March 2017 in America/New_York does not exist, so GetNamedTimeZoneEpochNanoseconds(
21.4.1.21 GetNamedTimeZoneOffsetNanoseconds (timeZoneIdentifier,epochNanoseconds )
The
The returned
The default implementation of GetNamedTimeZoneOffsetNanoseconds, to be used for ECMAScript implementations that do not include local political rules for any time zones, performs the following steps when called:
Assert :timeZoneIdentifier is"UTC" .- Return 0.
Time zone offset values may be positive or negative.
21.4.1.22 Time Zone Identifier Record
ATime Zone Identifier Record is a
Time Zone Identifier Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Identifier]] | a String | An |
| [[PrimaryIdentifier]] | a String | The |
If[[Identifier]] is a
21.4.1.23 AvailableNamedTimeZoneIdentifiers ( )
The
- If the implementation does not include local political rules for any time zones, then
- Return « the
Time Zone Identifier Record {[[Identifier]]:"UTC" ,[[PrimaryIdentifier]]:"UTC" } ».
- Return « the
- Letidentifiers be the
List of uniqueavailable named time zone identifiers . - Sortidentifiers into the same order as if an Array of the same values had been sorted using %Array.prototype.sort% with
undefined ascomparefn. - Letresult be a new empty
List . - For each elementidentifier ofidentifiers, do
- Letprimary beidentifier.
- Ifidentifier is a
non-primary time zone identifier in this implementation andidentifier is not"UTC" , then- Setprimary to the
primary time zone identifier associated withidentifier. - NOTE: An implementation may need to resolveidentifier iteratively to obtain the
primary time zone identifier .
- Setprimary to the
- Letrecord be the
Time Zone Identifier Record {[[Identifier]]:identifier,[[PrimaryIdentifier]]:primary }. - Appendrecord toresult.
Assert :result contains aTime Zone Identifier Record r such thatr.[[Identifier]] is"UTC" andr.[[PrimaryIdentifier]] is"UTC" .- Returnresult.
21.4.1.24 SystemTimeZoneIdentifier ( )
The
- If the implementation only supports the UTC time zone, return
"UTC" . - LetsystemTimeZoneString be the String representing the
host environment 's current time zone, either aprimary time zone identifier or anoffset time zone identifier. - ReturnsystemTimeZoneString.
To ensure the level of functionality that implementations commonly provide in the methods of the Date object, it is recommended that SystemTimeZoneIdentifier return an IANA time zone name corresponding to the
For example, if the
21.4.1.25 LocalTime (t )
The abstract operation LocalTime takes argumentt (a
- LetsystemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- LetoffsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- LetoffsetNs be
- Else,
- LetoffsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (t) × 106)).
- LetoffsetNs be
- LetoffsetMs be
truncate (offsetNs / 106). - Returnt +
𝔽 (offsetMs).
If political rules for the local timet are not available within the implementation, the result ist because
It is required for
Two different input
21.4.1.26 UTC (t )
The abstract operation UTC takes argumentt (a Number) and returns a
- Ift is not
finite , returnNaN . - LetsystemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- LetoffsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- LetoffsetNs be
- Else,
- LetpossibleInstants be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (t)),ℝ (MonthFromTime (t)) + 1,ℝ (DateFromTime (t)),ℝ (HourFromTime (t)),ℝ (MinFromTime (t)),ℝ (SecFromTime (t)),ℝ (msFromTime (t)), 0, 0). - NOTE: The following steps ensure that whent represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change),t is interpreted using the time zone offset before the transition.
- IfpossibleInstants is not empty, then
- LetdisambiguatedInstant bepossibleInstants[0].
- Else,
- NOTE:t represents a local time skipped at a positive time zone transition (e.g. due to daylight saving time starting or a time zone rule change increasing the UTC offset).
- LetpossibleInstantsBefore be
GetNamedTimeZoneEpochNanoseconds (systemTimeZoneIdentifier,ℝ (YearFromTime (tBefore)),ℝ (MonthFromTime (tBefore)) + 1,ℝ (DateFromTime (tBefore)),ℝ (HourFromTime (tBefore)),ℝ (MinFromTime (tBefore)),ℝ (SecFromTime (tBefore)),ℝ (msFromTime (tBefore)), 0, 0), wheretBefore is the largestintegral Number <t for whichpossibleInstantsBefore is not empty (i.e.,tBefore represents the last local time before the transition). - LetdisambiguatedInstant be the last element ofpossibleInstantsBefore.
- LetoffsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,disambiguatedInstant).
- LetpossibleInstants be
- LetoffsetMs be
truncate (offsetNs / 106). - Returnt -
𝔽 (offsetMs).
Inputt is nominally a
If political rules for the local timet are not available within the implementation, the result ist because
It is required for
1:30 AM on 5 November 2017 in America/New_York is repeated twice (fall backward), but it must be interpreted as 1:30 AM UTC-04 instead of 1:30 AM UTC-05. In UTC(
2:30 AM on 12 March 2017 in America/New_York does not exist, but it must be interpreted as 2:30 AM UTC-05 (equivalent to 3:30 AM UTC-04). In UTC(
21.4.1.27 MakeTime (hour,min,sec,ms )
The abstract operation MakeTime takes argumentshour (a Number),min (a Number),sec (a Number), andms (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- Ifhour is not
finite ,min is notfinite ,sec is notfinite , orms is notfinite , returnNaN . - Leth be
𝔽 (!ToIntegerOrInfinity (hour)). - Letm be
𝔽 (!ToIntegerOrInfinity (min)). - Lets be
𝔽 (!ToIntegerOrInfinity (sec)). - Letmilli be
𝔽 (!ToIntegerOrInfinity (ms)). - Return ((h ×
msPerHour +m ×msPerMinute ) +s ×msPerSecond ) +milli.
The arithmetic in MakeTime is floating-point arithmetic, which is not associative, so the operations must be performed in the correct order.
21.4.1.28 MakeDay (year,month,date )
The abstract operation MakeDay takes argumentsyear (a Number),month (a Number), anddate (a Number) and returns a Number. It calculates a number of days. It performs the following steps when called:
- Ifyear is not
finite ,month is notfinite , ordate is notfinite , returnNaN . - Lety be
𝔽 (!ToIntegerOrInfinity (year)). - Letm be
𝔽 (!ToIntegerOrInfinity (month)). - Letdt be
𝔽 (!ToIntegerOrInfinity (date)). - Letym bey +
𝔽 (floor (ℝ (m) / 12)). - Ifym is not
finite , returnNaN . - Letmn be
𝔽 (ℝ (m)modulo 12). - Find a
finite time value t such thatYearFromTime (t) isym,MonthFromTime (t) ismn, andDateFromTime (t) is1 𝔽; but if this is not possible (because some argument is out of range), returnNaN . - Return
Day (t) +dt -1 𝔽.
21.4.1.29 MakeDate (day,time )
The abstract operation MakeDate takes argumentsday (a Number) andtime (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
21.4.1.30 MakeFullYear (year )
The abstract operation MakeFullYear takes argumentyear (a Number) and returns an
- Ifyear is
NaN , returnNaN . - Lettruncated be !
ToIntegerOrInfinity (year). - Iftruncated is in the
inclusive interval from 0 to 99, return1900 𝔽 +𝔽 (truncated). - Return
𝔽 (truncated).
21.4.1.31 TimeClip (time )
The abstract operation TimeClip takes argumenttime (a Number) and returns a Number. It calculates a number of milliseconds. It performs the following steps when called:
- Iftime is not
finite , returnNaN . - If
abs (ℝ (time)) > 8.64 × 1015, returnNaN . - Return
𝔽 (!ToIntegerOrInfinity (time)).
21.4.1.32 Date Time String Format
ECMAScript defines a string interchange format for date-times based upon a simplification of the ISO 8601 calendar date extended format. The format is as follows:YYYY-MM-DDTHH:mm:ss.sssZ
Where the elements are as follows:
YYYY | is the year in the proleptic Gregorian calendar as four decimal digits from 0000 to 9999, or as an |
- | |
MM | is the month of the year as two decimal digits from 01 (January) to 12 (December). |
DD | is the day of the month as two decimal digits from 01 to 31. |
T | |
HH | is the number of complete hours that have passed since midnight as two decimal digits from 00 to 24. |
: | |
mm | is the number of complete minutes since the start of the hour as two decimal digits from 00 to 59. |
ss | is the number of complete seconds since the start of the minute as two decimal digits from 00 to 59. |
. | |
sss | is the number of complete milliseconds since the start of the second as three decimal digits. |
Z | is the UTC offset representation specified asHH:mm (a subset of the |
This format includes date-only forms:
YYYYYYYY-MMYYYY-MM-DD
It also includes “date-time” forms that consist of one of the above date-only forms immediately followed by one of the following time forms with an optional UTC offset representation appended:
THH:mmTHH:mm:ssTHH:mm:ss.sss
A string containing out-of-bounds or nonconforming elements is not a valid instance of this format.
As every day both starts and ends with midnight, the two notations00:00 and24:00 are available to distinguish the two midnights that can be associated with one date. This means that the following two notations refer to exactly the same point in time:1995-02-04T24:00 and1995-02-05T00:00. This interpretation of the latter form as "end of a calendar day" is consistent with ISO 8601, even though that specification reserves it for describing time intervals and does not permit it within representations of single points in time.
There exists no international standard that specifies abbreviations for civil time zones like CET, EST, etc. and sometimes the same abbreviation is even used for two very different time zones. For this reason, both ISO 8601 and this format specify numeric representations of time zone offsets.
21.4.1.32.1 Expanded Years
Covering the fullDate.parse
Examples of date-
| -271821-04-20T00:00:00Z | 271822 B.C. |
| -000001-01-01T00:00:00Z | 2 B.C. |
| +000000-01-01T00:00:00Z | 1 B.C. |
| +000001-01-01T00:00:00Z | 1 A.D. |
| +001970-01-01T00:00:00Z | 1970 A.D. |
| +002009-12-15T00:00:00Z | 2009 A.D. |
| +275760-09-13T00:00:00Z | 275760 A.D. |
21.4.1.33 Time Zone Offset String Format
ECMAScript defines a string interchange format for UTC offsets, derived from ISO 8601. The format is described by the following grammar. The usage of Unicode code points in this grammar is listed in
| Code Point | Unicode Name | Abbreviation |
|---|---|---|
U+2212 | MINUS SIGN | <MINUS> |
Syntax
21.4.1.33.1 IsTimeZoneOffsetString (offsetString )
The abstract operation IsTimeZoneOffsetString takes argumentoffsetString (a String) and returns a Boolean. The return value indicates whetheroffsetString conforms to the grammar given by
- LetparseResult be
ParseText (StringToCodePoints (offsetString),UTCOffset ). - IfparseResult is a
List of errors, returnfalse . - Return
true .
21.4.1.33.2 ParseTimeZoneOffsetString (offsetString )
The abstract operation ParseTimeZoneOffsetString takes argumentoffsetString (a String) and returns an
- LetparseResult be
ParseText (StringToCodePoints (offsetString),UTCOffset ). Assert :parseResult is not aList of errors.Assert :parseResult contains aTemporalSign Parse Node .- LetparsedSign be the
source text matched by theTemporalSign Parse Node contained withinparseResult. - IfparsedSign is the single code point U+002D (HYPHEN-MINUS) or U+2212 (MINUS SIGN), then
- Letsign be -1.
- Else,
- Letsign be 1.
- NOTE: Applications of
StringToNumber below do not lose precision, since each of the parsed values is guaranteed to be a sufficiently short string of decimal digits. Assert :parseResult contains anHour Parse Node .- LetparsedHours be the
source text matched by theHour Parse Node contained withinparseResult. - Lethours be
ℝ (StringToNumber (CodePointsToString (parsedHours))). - IfparseResult does not contain a
MinuteSecond Parse Node , then- Letminutes be 0.
- Else,
- LetparsedMinutes be the
source text matched by the firstMinuteSecond Parse Node contained withinparseResult. - Letminutes be
ℝ (StringToNumber (CodePointsToString (parsedMinutes))).
- LetparsedMinutes be the
- IfparseResult does not contain two
MinuteSecond Parse Nodes , then- Letseconds be 0.
- Else,
- LetparsedSeconds be the
source text matched by the secondMinuteSecond Parse Node contained withinparseResult. - Letseconds be
ℝ (StringToNumber (CodePointsToString (parsedSeconds))).
- LetparsedSeconds be the
- IfparseResult does not contain a
TemporalDecimalFraction Parse Node , then- Letnanoseconds be 0.
- Else,
- LetparsedFraction be the
source text matched by theTemporalDecimalFraction Parse Node contained withinparseResult. - Letfraction be the
string-concatenation ofCodePointsToString (parsedFraction) and"000000000" . - LetnanosecondsString be the
substring offraction from 1 to 10. - Letnanoseconds be
ℝ (StringToNumber (nanosecondsString)).
- LetparsedFraction be the
- Returnsign × (((hours × 60 +minutes) × 60 +seconds) × 109 +nanoseconds).
21.4.2 The Date Constructor
The Date
- is%Date%.
- is the initial value of the
"Date" property of theglobal object . - creates and initializes a new Date when called as a
constructor . - returns a String representing the current time (UTC) when called as a function rather than as a
constructor . - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Date behaviour must include asupercall to the Dateconstructor to create and initialize the subclass instance with a[[DateValue]] internal slot.
21.4.2.1 Date ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , then- Letnow be the
time value (UTC) identifying the current time. - Return
ToDateString (now).
- Letnow be the
- LetnumberOfArgs be the number of elements invalues.
- IfnumberOfArgs = 0, then
- Letdv be the
time value (UTC) identifying the current time.
- Letdv be the
- Else ifnumberOfArgs = 1, then
- Letvalue bevalues[0].
- Ifvalue
is an Object andvalue has a[[DateValue]] internal slot, then- Lettv bevalue.[[DateValue]].
- Else,
- Letv be ?
ToPrimitive (value). - Ifv
is a String , thenAssert : The next step never returns anabrupt completion becausevis a String .- Lettv be the result of parsingv as a date, in exactly the same manner as for the
parsemethod (21.4.3.2 ).
- Else,
- Lettv be ?
ToNumber (v).
- Lettv be ?
- Letv be ?
- Letdv be
TimeClip (tv).
- Else,
Assert :numberOfArgs ≥ 2.- Lety be ?
ToNumber (values[0]). - Letm be ?
ToNumber (values[1]). - IfnumberOfArgs > 2, letdt be ?
ToNumber (values[2]); else letdt be1 𝔽. - IfnumberOfArgs > 3, leth be ?
ToNumber (values[3]); else leth be+0 𝔽. - IfnumberOfArgs > 4, letmin be ?
ToNumber (values[4]); else letmin be+0 𝔽. - IfnumberOfArgs > 5, lets be ?
ToNumber (values[5]); else lets be+0 𝔽. - IfnumberOfArgs > 6, letmilli be ?
ToNumber (values[6]); else letmilli be+0 𝔽. - Letyr be
MakeFullYear (y). - LetfinalDate be
MakeDate (MakeDay (yr,m,dt),MakeTime (h,min,s,milli)). - Letdv be
TimeClip (UTC (finalDate)).
- LetO be ?
OrdinaryCreateFromConstructor (NewTarget,"%Date.prototype%" , «[[DateValue]] »). - SetO.[[DateValue]] todv.
- ReturnO.
21.4.3 Properties of the Date Constructor
The Date
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is7 𝔽. - has the following properties:
21.4.3.1 Date.now ( )
This function returns the
21.4.3.2 Date.parse (string )
This function applies the
If the String conforms to theMM orDD elements are absent,HH,mm, orss elements are absent,sss element is absent,
Ifx is any Date whose milliseconds amount is zero within a particular implementation of ECMAScript, then all of the following expressions should produce the same numeric value in that implementation, if all the properties referenced have their initial values:
x.valueOf()Date.parse(x.toString())Date.parse(x.toUTCString())Date.parse(x.toISOString())However, the expression
Date.parse(x.toLocaleString())is not required to produce the same Number value as the preceding three expressions and, in general, the value produced by this function istoString ortoUTCString method.
21.4.3.3 Date.prototype
The initial value ofDate.prototype is the
This property has the attributes {[[Writable]]:
21.4.3.4 Date.UTC (year [ ,month [ ,date [ ,hours [ ,minutes [ ,seconds [ ,ms ] ] ] ] ] ] )
This function performs the following steps when called:
- Lety be ?
ToNumber (year). - Ifmonth is present, letm be ?
ToNumber (month); else letm be+0 𝔽. - Ifdate is present, letdt be ?
ToNumber (date); else letdt be1 𝔽. - Ifhours is present, leth be ?
ToNumber (hours); else leth be+0 𝔽. - Ifminutes is present, letmin be ?
ToNumber (minutes); else letmin be+0 𝔽. - Ifseconds is present, lets be ?
ToNumber (seconds); else lets be+0 𝔽. - Ifms is present, letmilli be ?
ToNumber (ms); else letmilli be+0 𝔽. - Letyr be
MakeFullYear (y). - Return
TimeClip (MakeDate (MakeDay (yr,m,dt),MakeTime (h,min,s,milli))).
The
This function differs from the Date
21.4.4 Properties of the Date Prototype Object
TheDate prototype object:
- is%Date.prototype%.
- is itself an
ordinary object . - is not a Date instance and does not have a[[DateValue]] internal slot.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly defined otherwise, the methods of the Date prototype object defined below are not generic and the
21.4.4.1 Date.prototype.constructor
The initial value ofDate.prototype.constructor is
21.4.4.2 Date.prototype.getDate ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
DateFromTime (LocalTime (t)).
21.4.4.3 Date.prototype.getDay ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
WeekDay (LocalTime (t)).
21.4.4.4 Date.prototype.getFullYear ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)).
21.4.4.5 Date.prototype.getHours ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
HourFromTime (LocalTime (t)).
21.4.4.6 Date.prototype.getMilliseconds ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
msFromTime (LocalTime (t)).
21.4.4.7 Date.prototype.getMinutes ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
MinFromTime (LocalTime (t)).
21.4.4.8 Date.prototype.getMonth ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
MonthFromTime (LocalTime (t)).
21.4.4.9 Date.prototype.getSeconds ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
SecFromTime (LocalTime (t)).
21.4.4.10 Date.prototype.getTime ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - ReturndateObject.[[DateValue]].
21.4.4.11 Date.prototype.getTimezoneOffset ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return (t -
LocalTime (t)) /msPerMinute .
21.4.4.12 Date.prototype.getUTCDate ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
DateFromTime (t).
21.4.4.13 Date.prototype.getUTCDay ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
WeekDay (t).
21.4.4.14 Date.prototype.getUTCFullYear ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
YearFromTime (t).
21.4.4.15 Date.prototype.getUTCHours ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
HourFromTime (t).
21.4.4.16 Date.prototype.getUTCMilliseconds ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
msFromTime (t).
21.4.4.17 Date.prototype.getUTCMinutes ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
MinFromTime (t).
21.4.4.18 Date.prototype.getUTCMonth ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
MonthFromTime (t).
21.4.4.19 Date.prototype.getUTCSeconds ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
SecFromTime (t).
21.4.4.20 Date.prototype.setDate (date )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letdt be ?
ToNumber (date). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - LetnewDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t),dt),TimeWithinDay (t)). - Letu be
TimeClip (UTC (newDate)). - SetdateObject.[[DateValue]] tou.
- Returnu.
21.4.4.21 Date.prototype.setFullYear (year [ ,month [ ,date ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Lety be ?
ToNumber (year). - Ift is
NaN , sett to+0 𝔽; otherwise, sett toLocalTime (t). - Ifmonth is not present, letm be
MonthFromTime (t); otherwise, letm be ?ToNumber (month). - Ifdate is not present, letdt be
DateFromTime (t); otherwise, letdt be ?ToNumber (date). - LetnewDate be
MakeDate (MakeDay (y,m,dt),TimeWithinDay (t)). - Letu be
TimeClip (UTC (newDate)). - SetdateObject.[[DateValue]] tou.
- Returnu.
The
Ifmonth is not present, this method behaves as ifmonth was present with the valuegetMonth(). Ifdate is not present, it behaves as ifdate was present with the valuegetDate().
21.4.4.22 Date.prototype.setHours (hour [ ,min [ ,sec [ ,ms ] ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Leth be ?
ToNumber (hour). - Ifmin is present, letm be ?
ToNumber (min). - Ifsec is present, lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - Ifmin is not present, letm be
MinFromTime (t). - Ifsec is not present, lets be
SecFromTime (t). - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (h,m,s,milli)). - Letu be
TimeClip (UTC (date)). - SetdateObject.[[DateValue]] tou.
- Returnu.
The
Ifmin is not present, this method behaves as ifmin was present with the valuegetMinutes(). Ifsec is not present, it behaves as ifsec was present with the valuegetSeconds(). Ifms is not present, it behaves as ifms was present with the valuegetMilliseconds().
21.4.4.23 Date.prototype.setMilliseconds (ms )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Setms to ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - Lettime be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t),ms). - Letu be
TimeClip (UTC (MakeDate (Day (t),time))). - SetdateObject.[[DateValue]] tou.
- Returnu.
21.4.4.24 Date.prototype.setMinutes (min [ ,sec [ ,ms ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letm be ?
ToNumber (min). - Ifsec is present, lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - Ifsec is not present, lets be
SecFromTime (t). - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (HourFromTime (t),m,s,milli)). - Letu be
TimeClip (UTC (date)). - SetdateObject.[[DateValue]] tou.
- Returnu.
The
Ifsec is not present, this method behaves as ifsec was present with the valuegetSeconds(). Ifms is not present, this behaves as ifms was present with the valuegetMilliseconds().
21.4.4.25 Date.prototype.setMonth (month [ ,date ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letm be ?
ToNumber (month). - Ifdate is present, letdt be ?
ToNumber (date). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - Ifdate is not present, letdt be
DateFromTime (t). - LetnewDate be
MakeDate (MakeDay (YearFromTime (t),m,dt),TimeWithinDay (t)). - Letu be
TimeClip (UTC (newDate)). - SetdateObject.[[DateValue]] tou.
- Returnu.
The
Ifdate is not present, this method behaves as ifdate was present with the valuegetDate().
21.4.4.26 Date.prototype.setSeconds (sec [ ,ms ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Sett to
LocalTime (t). - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t),s,milli)). - Letu be
TimeClip (UTC (date)). - SetdateObject.[[DateValue]] tou.
- Returnu.
The
Ifms is not present, this method behaves as ifms was present with the valuegetMilliseconds().
21.4.4.27 Date.prototype.setTime (time )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett be ?
ToNumber (time). - Letv be
TimeClip (t). - SetdateObject.[[DateValue]] tov.
- Returnv.
21.4.4.28 Date.prototype.setUTCDate (date )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letdt be ?
ToNumber (date). - Ift is
NaN , returnNaN . - LetnewDate be
MakeDate (MakeDay (YearFromTime (t),MonthFromTime (t),dt),TimeWithinDay (t)). - Letv be
TimeClip (newDate). - SetdateObject.[[DateValue]] tov.
- Returnv.
21.4.4.29 Date.prototype.setUTCFullYear (year [ ,month [ ,date ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , sett to+0 𝔽. - Lety be ?
ToNumber (year). - Ifmonth is not present, letm be
MonthFromTime (t); otherwise, letm be ?ToNumber (month). - Ifdate is not present, letdt be
DateFromTime (t); otherwise, letdt be ?ToNumber (date). - LetnewDate be
MakeDate (MakeDay (y,m,dt),TimeWithinDay (t)). - Letv be
TimeClip (newDate). - SetdateObject.[[DateValue]] tov.
- Returnv.
The
Ifmonth is not present, this method behaves as ifmonth was present with the valuegetUTCMonth(). Ifdate is not present, it behaves as ifdate was present with the valuegetUTCDate().
21.4.4.30 Date.prototype.setUTCHours (hour [ ,min [ ,sec [ ,ms ] ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Leth be ?
ToNumber (hour). - Ifmin is present, letm be ?
ToNumber (min). - Ifsec is present, lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Ifmin is not present, letm be
MinFromTime (t). - Ifsec is not present, lets be
SecFromTime (t). - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (h,m,s,milli)). - Letv be
TimeClip (date). - SetdateObject.[[DateValue]] tov.
- Returnv.
The
Ifmin is not present, this method behaves as ifmin was present with the valuegetUTCMinutes(). Ifsec is not present, it behaves as ifsec was present with the valuegetUTCSeconds(). Ifms is not present, it behaves as ifms was present with the valuegetUTCMilliseconds().
21.4.4.31 Date.prototype.setUTCMilliseconds (ms )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Setms to ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Lettime be
MakeTime (HourFromTime (t),MinFromTime (t),SecFromTime (t),ms). - Letv be
TimeClip (MakeDate (Day (t),time)). - SetdateObject.[[DateValue]] tov.
- Returnv.
21.4.4.32 Date.prototype.setUTCMinutes (min [ ,sec [ ,ms ] ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letm be ?
ToNumber (min). - Ifsec is present, lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Ifsec is not present, lets be
SecFromTime (t). - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (HourFromTime (t),m,s,milli)). - Letv be
TimeClip (date). - SetdateObject.[[DateValue]] tov.
- Returnv.
The
Ifsec is not present, this method behaves as ifsec was present with the valuegetUTCSeconds(). Ifms is not present, it behaves as ifms was present with the value return bygetUTCMilliseconds().
21.4.4.33 Date.prototype.setUTCMonth (month [ ,date ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Letm be ?
ToNumber (month). - Ifdate is present, letdt be ?
ToNumber (date). - Ift is
NaN , returnNaN . - Ifdate is not present, letdt be
DateFromTime (t). - LetnewDate be
MakeDate (MakeDay (YearFromTime (t),m,dt),TimeWithinDay (t)). - Letv be
TimeClip (newDate). - SetdateObject.[[DateValue]] tov.
- Returnv.
The
Ifdate is not present, this method behaves as ifdate was present with the valuegetUTCDate().
21.4.4.34 Date.prototype.setUTCSeconds (sec [ ,ms ] )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Lets be ?
ToNumber (sec). - Ifms is present, letmilli be ?
ToNumber (ms). - Ift is
NaN , returnNaN . - Ifms is not present, letmilli be
msFromTime (t). - Letdate be
MakeDate (Day (t),MakeTime (HourFromTime (t),MinFromTime (t),s,milli)). - Letv be
TimeClip (date). - SetdateObject.[[DateValue]] tov.
- Returnv.
The
Ifms is not present, this method behaves as ifms was present with the valuegetUTCMilliseconds().
21.4.4.35 Date.prototype.toDateString ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lettv bedateObject.[[DateValue]].
- Iftv is
NaN , return"Invalid Date" . - Lett be
LocalTime (tv). - Return
DateString (t).
21.4.4.36 Date.prototype.toISOString ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lettv bedateObject.[[DateValue]].
- Iftv is not
finite , throw aRangeError exception. - Iftv corresponds with a year that cannot be represented in the
Date Time String Format , throw aRangeError exception. - Return a String representation oftv in the
Date Time String Format on the UTC time scale, including all format elements and the UTC offset representation"Z" .
21.4.4.37 Date.prototype.toJSON (key )
This method provides a String representation of a Date for use byJSON.stringify (
It performs the following steps when called:
- LetO be ?
ToObject (this value). - Lettv be ?
ToPrimitive (O,number ). - Iftv
is a Number andtv is notfinite , returnnull . - Return ?
Invoke (O,"toISOString" ).
The argument is ignored.
This method is intentionally generic; it does not require that itstoISOString method.
21.4.4.38 Date.prototype.toLocaleDateString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.39 Date.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.40 Date.prototype.toLocaleTimeString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a String value. The contents of the String are
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
21.4.4.41 Date.prototype.toString ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lettv bedateObject.[[DateValue]].
- Return
ToDateString (tv).
For any Dated such thatd.[[DateValue]] is evenly divisible by 1000, the result ofDate.parse(d.toString()) =d.valueOf(). See
This method is not generic; it throws a
21.4.4.41.1 TimeString (tv )
The abstract operation TimeString takes argumenttv (a Number, but not
- Lethour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (tv)), 2). - Letminute be
ToZeroPaddedDecimalString (ℝ (MinFromTime (tv)), 2). - Letsecond be
ToZeroPaddedDecimalString (ℝ (SecFromTime (tv)), 2). - Return the
string-concatenation ofhour,":" ,minute,":" ,second, the code unit 0x0020 (SPACE), and"GMT" .
21.4.4.41.2 DateString (tv )
The abstract operation DateString takes argumenttv (a Number, but not
- Letweekday be the Name of the entry in
Table 63 with the NumberWeekDay (tv). - Letmonth be the Name of the entry in
Table 64 with the NumberMonthFromTime (tv). - Letday be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Letyv be
YearFromTime (tv). - Ifyv is
+0 𝔽 oryv >+0 𝔽, letyearSign be the empty String; otherwise, letyearSign be"-" . - LetpaddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation ofweekday, the code unit 0x0020 (SPACE),month, the code unit 0x0020 (SPACE),day, the code unit 0x0020 (SPACE),yearSign, andpaddedYear.
| Number | Name |
|---|---|
| Number | Name |
|---|---|
21.4.4.41.3 TimeZoneString (tv )
The abstract operation TimeZoneString takes argumenttv (an
- LetsystemTimeZoneIdentifier be
SystemTimeZoneIdentifier (). - If
IsTimeZoneOffsetString (systemTimeZoneIdentifier) istrue , then- LetoffsetNs be
ParseTimeZoneOffsetString (systemTimeZoneIdentifier).
- LetoffsetNs be
- Else,
- LetoffsetNs be
GetNamedTimeZoneOffsetNanoseconds (systemTimeZoneIdentifier,ℤ (ℝ (tv) × 106)).
- LetoffsetNs be
- Letoffset be
𝔽 (truncate (offsetNs / 106)). - Ifoffset is
+0 𝔽 oroffset >+0 𝔽, then- LetoffsetSign be
"+" . - LetabsOffset beoffset.
- LetoffsetSign be
- Else,
- LetoffsetSign be
"-" . - LetabsOffset be -offset.
- LetoffsetSign be
- LetoffsetMin be
ToZeroPaddedDecimalString (ℝ (MinFromTime (absOffset)), 2). - LetoffsetHour be
ToZeroPaddedDecimalString (ℝ (HourFromTime (absOffset)), 2). - LettzName be an
implementation-defined string that is either the empty String or thestring-concatenation of the code unit 0x0020 (SPACE), the code unit 0x0028 (LEFT PARENTHESIS), animplementation-defined timezone name, and the code unit 0x0029 (RIGHT PARENTHESIS). - Return the
string-concatenation ofoffsetSign,offsetHour,offsetMin, andtzName.
21.4.4.41.4 ToDateString (tv )
The abstract operation ToDateString takes argumenttv (an
- Iftv is
NaN , return"Invalid Date" . - Lett be
LocalTime (tv). - Return the
string-concatenation ofDateString (t), the code unit 0x0020 (SPACE),TimeString (t), andTimeZoneString (tv).
21.4.4.42 Date.prototype.toTimeString ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lettv bedateObject.[[DateValue]].
- Iftv is
NaN , return"Invalid Date" . - Lett be
LocalTime (tv). - Return the
string-concatenation ofTimeString (t) andTimeZoneString (tv).
21.4.4.43 Date.prototype.toUTCString ( )
This method returns a String value representing the instant in time corresponding to the
It performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lettv bedateObject.[[DateValue]].
- Iftv is
NaN , return"Invalid Date" . - Letweekday be the Name of the entry in
Table 63 with the NumberWeekDay (tv). - Letmonth be the Name of the entry in
Table 64 with the NumberMonthFromTime (tv). - Letday be
ToZeroPaddedDecimalString (ℝ (DateFromTime (tv)), 2). - Letyv be
YearFromTime (tv). - Ifyv is
+0 𝔽 oryv >+0 𝔽, letyearSign be the empty String; otherwise, letyearSign be"-" . - LetpaddedYear be
ToZeroPaddedDecimalString (abs (ℝ (yv)), 4). - Return the
string-concatenation ofweekday,"," , the code unit 0x0020 (SPACE),day, the code unit 0x0020 (SPACE),month, the code unit 0x0020 (SPACE),yearSign,paddedYear, the code unit 0x0020 (SPACE), andTimeString (tv).
21.4.4.44 Date.prototype.valueOf ( )
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - ReturndateObject.[[DateValue]].
21.4.4.45 Date.prototype [ @@toPrimitive ] (hint )
This method is called by ECMAScript language operators to convert a Date to a primitive value. The allowed values forhint are
It performs the following steps when called:
- LetO be the
this value. - IfO
is not an Object , throw aTypeError exception. - Ifhint is either
"string" or"default" , then- LettryFirst be
string .
- LettryFirst be
- Else ifhint is
"number" , then- LettryFirst be
number .
- LettryFirst be
- Else,
- Throw a
TypeError exception.
- Throw a
- Return ?
OrdinaryToPrimitive (O,tryFirst).
This property has the attributes {[[Writable]]:
The value of the
21.4.5 Properties of Date Instances
Date instances are
22 Text Processing
22.1 String Objects
22.1.1 The String Constructor
The String
- is%String%.
- is the initial value of the
"String" property of theglobal object . - creates and initializes a new String object when called as a
constructor . - performs a type conversion when called as a function rather than as a
constructor . - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified String behaviour must include asupercall to the Stringconstructor to create and initialize the subclass instance with a[[StringData]] internal slot.
22.1.1.1 String (value )
This function performs the following steps when called:
- Ifvalue is not present, then
- Lets be the empty String.
- Else,
- If NewTarget is
undefined andvalueis a Symbol , returnSymbolDescriptiveString (value). - Lets be ?
ToString (value).
- If NewTarget is
- If NewTarget is
undefined , returns. - Return
StringCreate (s, ?GetPrototypeFromConstructor (NewTarget,"%String.prototype%" )).
22.1.2 Properties of the String Constructor
The String
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.1.2.1 String.fromCharCode ( ...codeUnits )
This function may be called with any number of arguments which form the rest parametercodeUnits.
It performs the following steps when called:
- Letresult be the empty String.
- For each elementnext ofcodeUnits, do
- LetnextCU be the code unit whose numeric value is
ℝ (?ToUint16 (next)). - Setresult to the
string-concatenation ofresult andnextCU.
- LetnextCU be the code unit whose numeric value is
- Returnresult.
The
22.1.2.2 String.fromCodePoint ( ...codePoints )
This function may be called with any number of arguments which form the rest parametercodePoints.
It performs the following steps when called:
- Letresult be the empty String.
- For each elementnext ofcodePoints, do
- LetnextCP be ?
ToNumber (next). - If
IsIntegralNumber (nextCP) isfalse , throw aRangeError exception. - If
ℝ (nextCP) < 0 orℝ (nextCP) > 0x10FFFF, throw aRangeError exception. - Setresult to the
string-concatenation ofresult andUTF16EncodeCodePoint (ℝ (nextCP)).
- LetnextCP be ?
Assert : IfcodePoints is empty, thenresult is the empty String.- Returnresult.
The
22.1.2.3 String.prototype
The initial value ofString.prototype is the
This property has the attributes {[[Writable]]:
22.1.2.4 String.raw (template, ...substitutions )
This function may be called with a variable number of arguments. The first argument istemplate and the remainder of the arguments form the
It performs the following steps when called:
- LetsubstitutionCount be the number of elements insubstitutions.
- Letcooked be ?
ToObject (template). - Letliterals be ?
ToObject (?Get (cooked,"raw" )). - LetliteralCount be ?
LengthOfArrayLike (literals). - IfliteralCount ≤ 0, return the empty String.
- LetR be the empty String.
- LetnextIndex be 0.
- Repeat,
- LetnextLiteralVal be ?
Get (literals, !ToString (𝔽 (nextIndex))). - LetnextLiteral be ?
ToString (nextLiteralVal). - SetR to the
string-concatenation ofR andnextLiteral. - IfnextIndex + 1 =literalCount, returnR.
- IfnextIndex <substitutionCount, then
- LetnextSubVal besubstitutions[nextIndex].
- LetnextSub be ?
ToString (nextSubVal). - SetR to the
string-concatenation ofR andnextSub.
- SetnextIndex tonextIndex + 1.
- LetnextLiteralVal be ?
This function is intended for use as a tag function of a Tagged Template (
22.1.3 Properties of the String Prototype Object
TheString prototype object:
- is%String.prototype%.
is a String exotic object and has the internal methods specified for such objects.- has a[[StringData]] internal slot whose value is the empty String.
- has a
"length" property whose initial value is+0 𝔽 and whose attributes are {[[Writable]]:false ,[[Enumerable]]:false ,[[Configurable]]:false }. - has a[[Prototype]] internal slot whose value is
%Object.prototype% .
Unless explicitly stated otherwise, the methods of the String prototype object defined below are not generic and the
22.1.3.1 String.prototype.at (index )
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letlen be the length ofS.
- LetrelativeIndex be ?
ToIntegerOrInfinity (index). - IfrelativeIndex ≥ 0, then
- Letk berelativeIndex.
- Else,
- Letk belen +relativeIndex.
- Ifk < 0 ork ≥len, return
undefined . - Return the
substring ofS fromk tok + 1.
22.1.3.2 String.prototype.charAt (pos )
This method returns a single element String containing the code unit at indexpos within the String value resulting from converting this object to a String. If there is no element at that index, the result is the empty String. The result
Ifpos is anx.charAt(pos) is equivalent to the result ofx.substring(pos, pos + 1).
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letposition be ?
ToIntegerOrInfinity (pos). - Letsize be the length ofS.
- Ifposition < 0 orposition ≥size, return the empty String.
- Return the
substring ofS fromposition toposition + 1.
This method is intentionally generic; it does not require that its
22.1.3.3 String.prototype.charCodeAt (pos )
This method returns a Number (a non-negative
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letposition be ?
ToIntegerOrInfinity (pos). - Letsize be the length ofS.
- Ifposition < 0 orposition ≥size, return
NaN . - Return the
Number value for the numeric value of the code unit at indexposition within the StringS.
This method is intentionally generic; it does not require that its
22.1.3.4 String.prototype.codePointAt (pos )
This method returns a non-negative
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letposition be ?
ToIntegerOrInfinity (pos). - Letsize be the length ofS.
- Ifposition < 0 orposition ≥size, return
undefined . - Letcp be
CodePointAt (S,position). - Return
𝔽 (cp.[[CodePoint]]).
This method is intentionally generic; it does not require that its
22.1.3.5 String.prototype.concat ( ...args )
When this method is called it returns the String value consisting of the code units of the
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetR beS.
- For each elementnext ofargs, do
- LetnextString be ?
ToString (next). - SetR to the
string-concatenation ofR andnextString.
- LetnextString be ?
- ReturnR.
The
This method is intentionally generic; it does not require that its
22.1.3.6 String.prototype.constructor
The initial value ofString.prototype.constructor is
22.1.3.7 String.prototype.endsWith (searchString [ ,endPosition ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetisRegExp be ?
IsRegExp (searchString). - IfisRegExp is
true , throw aTypeError exception. - LetsearchStr be ?
ToString (searchString). - Letlen be the length ofS.
- IfendPosition is
undefined , letpos belen; else letpos be ?ToIntegerOrInfinity (endPosition). - Letend be the result of
clamping pos between 0 andlen. - LetsearchLength be the length ofsearchStr.
- IfsearchLength = 0, return
true . - Letstart beend -searchLength.
- Ifstart < 0, return
false . - Letsubstring be the
substring ofS fromstart toend. - Ifsubstring issearchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.8 String.prototype.includes (searchString [ ,position ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetisRegExp be ?
IsRegExp (searchString). - IfisRegExp is
true , throw aTypeError exception. - LetsearchStr be ?
ToString (searchString). - Letpos be ?
ToIntegerOrInfinity (position). Assert : Ifposition isundefined , thenpos is 0.- Letlen be the length ofS.
- Letstart be the result of
clamping pos between 0 andlen. - Letindex be
StringIndexOf (S,searchStr,start). - Ifindex ≠ -1, return
true . - Return
false .
IfsearchString appears as a
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.9 String.prototype.indexOf (searchString [ ,position ] )
IfsearchString appears as a
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetsearchStr be ?
ToString (searchString). - Letpos be ?
ToIntegerOrInfinity (position). Assert : Ifposition isundefined , thenpos is 0.- Letlen be the length ofS.
- Letstart be the result of
clamping pos between 0 andlen. - Return
𝔽 (StringIndexOf (S,searchStr,start)).
This method is intentionally generic; it does not require that its
22.1.3.10 String.prototype.isWellFormed ( )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Return
IsStringWellFormedUnicode (S).
22.1.3.11 String.prototype.lastIndexOf (searchString [ ,position ] )
IfsearchString appears as a
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetsearchStr be ?
ToString (searchString). - LetnumPos be ?
ToNumber (position). Assert : Ifposition isundefined , thennumPos isNaN .- IfnumPos is
NaN , letpos be +∞; otherwise, letpos be !ToIntegerOrInfinity (numPos). - Letlen be the length ofS.
- LetsearchLen be the length ofsearchStr.
- Letstart be the result of
clamping pos between 0 andlen -searchLen. - IfsearchStr is the empty String, return
𝔽 (start). - For each
integer i such that 0 ≤i ≤start, in descending order, do - Return
-1 𝔽.
This method is intentionally generic; it does not require that its
22.1.3.12 String.prototype.localeCompare (that [ ,reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method returns a Number other than
Before performing the comparisons, this method performs the following steps to prepare the Strings:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetthatValue be ?
ToString (that).
The meaning of the optional second and third parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not assign any other interpretation to those parameter positions.
The actual return values are
This method itself is not directly suitable as an argument toArray.prototype.sort because the latter requires a function of two arguments.
This method may rely on whatever language- and/or locale-sensitive comparison functionality is available to the ECMAScript environment from the
// Å ANGSTROM SIGN vs.// Å LATIN CAPITAL LETTER A + COMBINING RING ABOVE"\u212B".localeCompare("A\u030A")// Ω OHM SIGN vs.// Ω GREEK CAPITAL LETTER OMEGA"\u2126".localeCompare("\u03A9")// ṩ LATIN SMALL LETTER S WITH DOT BELOW AND DOT ABOVE vs.// ṩ LATIN SMALL LETTER S + COMBINING DOT ABOVE + COMBINING DOT BELOW"\u1E69".localeCompare("s\u0307\u0323")// ḍ̇ LATIN SMALL LETTER D WITH DOT ABOVE + COMBINING DOT BELOW vs.// ḍ̇ LATIN SMALL LETTER D WITH DOT BELOW + COMBINING DOT ABOVE"\u1E0B\u0323".localeCompare("\u1E0D\u0307")// 가 HANGUL CHOSEONG KIYEOK + HANGUL JUNGSEONG A vs.// 가 HANGUL SYLLABLE GA"\u1100\u1161".localeCompare("\uAC00")For a definition and discussion of canonical equivalence see the Unicode Standard, chapters 2 and 3, as well asUnicode Standard Annex #15, Unicode Normalization Forms andUnicode Technical Note #5, Canonical Equivalence in Applications. Also seeUnicode Technical Standard #10, Unicode Collation Algorithm.
It is recommended that this method should not honour Unicode compatibility equivalents or compatibility decompositions as defined in the Unicode Standard, chapter 3, section 3.7.
This method is intentionally generic; it does not require that its
22.1.3.13 String.prototype.match (regexp )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Ifregexp is neither
undefined nornull , then - LetS be ?
ToString (O). - Letrx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,@@match , «S »).
This method is intentionally generic; it does not require that its
22.1.3.14 String.prototype.matchAll (regexp )
This method performs a regular expression match of the String representing the
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Ifregexp is neither
undefined nornull , then- LetisRegExp be ?
IsRegExp (regexp). - IfisRegExp is
true , then- Letflags be ?
Get (regexp,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Letflags be ?
- Letmatcher be ?
GetMethod (regexp,@@matchAll ). - Ifmatcher is not
undefined , then- Return ?
Call (matcher,regexp, «O »).
- Return ?
- LetisRegExp be ?
- LetS be ?
ToString (O). - Letrx be ?
RegExpCreate (regexp,"g" ). - Return ?
Invoke (rx,@@matchAll , «S »).
String.prototype.split,String.prototype.matchAll is designed to typically act without mutating its inputs.22.1.3.15 String.prototype.normalize ( [form ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Ifform is
undefined , letf be"NFC" . - Else, letf be ?
ToString (form). - Iff is not one of
"NFC" ,"NFD" ,"NFKC" , or"NFKD" , throw aRangeError exception. - Letns be the String value that is the result of normalizingS into the normalization form named byf as specified inthe latest Unicode Standard, Normalization Forms.
- Returnns.
This method is intentionally generic; it does not require that its
22.1.3.16 String.prototype.padEnd (maxLength [ ,fillString ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O,maxLength,fillString,end ).
22.1.3.17 String.prototype.padStart (maxLength [ ,fillString ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Return ?
StringPaddingBuiltinsImpl (O,maxLength,fillString,start ).
22.1.3.17.1 StringPaddingBuiltinsImpl (O,maxLength,fillString,placement )
The abstract operation StringPaddingBuiltinsImpl takes argumentsO (an
- LetS be ?
ToString (O). - LetintMaxLength be
ℝ (?ToLength (maxLength)). - LetstringLength be the length ofS.
- IfintMaxLength ≤stringLength, returnS.
- IffillString is
undefined , setfillString to the String value consisting solely of the code unit 0x0020 (SPACE). - Else, setfillString to ?
ToString (fillString). - Return
StringPad (S,intMaxLength,fillString,placement).
22.1.3.17.2 StringPad (S,maxLength,fillString,placement )
The abstract operation StringPad takes argumentsS (a String),maxLength (a non-negative
- LetstringLength be the length ofS.
- IfmaxLength ≤stringLength, returnS.
- IffillString is the empty String, returnS.
- LetfillLen bemaxLength -stringLength.
- LettruncatedStringFiller be the String value consisting of repeated concatenations offillString truncated to lengthfillLen.
- Ifplacement is
start , return thestring-concatenation oftruncatedStringFiller andS. - Else, return the
string-concatenation ofS andtruncatedStringFiller.
The argumentmaxLength will be clamped such that it can be no smaller than the length ofS.
The argumentfillString defaults to
22.1.3.17.3 ToZeroPaddedDecimalString (n,minLength )
The abstract operation ToZeroPaddedDecimalString takes argumentsn (a non-negative
- LetS be the String representation ofn, formatted as a decimal number.
- Return
StringPad (S,minLength,"0" ,start ).
22.1.3.18 String.prototype.repeat (count )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letn be ?
ToIntegerOrInfinity (count). - Ifn < 0 orn = +∞, throw a
RangeError exception. - Ifn = 0, return the empty String.
- Return the String value that is made fromn copies ofS appended together.
This method creates the String value consisting of the code units of the
This method is intentionally generic; it does not require that its
22.1.3.19 String.prototype.replace (searchValue,replaceValue )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - IfsearchValue is neither
undefined nornull , then - Letstring be ?
ToString (O). - LetsearchString be ?
ToString (searchValue). - LetfunctionalReplace be
IsCallable (replaceValue). - IffunctionalReplace is
false , then- SetreplaceValue to ?
ToString (replaceValue).
- SetreplaceValue to ?
- LetsearchLength be the length ofsearchString.
- Letposition be
StringIndexOf (string,searchString, 0). - Ifposition = -1, returnstring.
- Letpreceding be the
substring ofstring from 0 toposition. - Letfollowing be the
substring ofstring fromposition +searchLength. - IffunctionalReplace is
true , then - Else,
Assert :replaceValueis a String .- Letcaptures be a new empty
List . - Letreplacement be !
GetSubstitution (searchString,string,position,captures,undefined ,replaceValue).
- Return the
string-concatenation ofpreceding,replacement, andfollowing.
This method is intentionally generic; it does not require that its
22.1.3.19.1 GetSubstitution (matched,str,position,captures,namedCaptures,replacementTemplate )
The abstract operation GetSubstitution takes argumentsmatched (a String),str (a String),position (a non-negative
- LetstringLength be the length ofstr.
Assert :position ≤stringLength.- Letresult be the empty String.
- LettemplateRemainder bereplacementTemplate.
- Repeat, whiletemplateRemainder is not the empty String,
- NOTE: The following steps isolateref (a prefix oftemplateRemainder), determinerefReplacement (its replacement), and then append that replacement toresult.
- IftemplateRemainder starts with
"$$" , then- Letref be
"$$" . - LetrefReplacement be
"$" .
- Letref be
- Else iftemplateRemainder starts with
"$`" , then- Letref be
"$`" . - LetrefReplacement be the
substring ofstr from 0 toposition.
- Letref be
- Else iftemplateRemainder starts with
"$&" , then- Letref be
"$&" . - LetrefReplacement bematched.
- Letref be
- Else iftemplateRemainder starts with
"$'" (0x0024 (DOLLAR SIGN) followed by 0x0027 (APOSTROPHE)), then- Letref be
"$'" . - LetmatchLength be the length ofmatched.
- LettailPos beposition +matchLength.
- LetrefReplacement be the
substring ofstr frommin (tailPos,stringLength). - NOTE:tailPos can exceedstringLength only if this abstract operation was invoked by a call to the intrinsic
@@replace method of%RegExp.prototype% on an object whose"exec" property is not the intrinsic %RegExp.prototype.exec%.
- Letref be
- Else iftemplateRemainder starts with
"$" followed by 1 or more decimal digits, then- IftemplateRemainder starts with
"$" followed by 2 or more decimal digits, letdigitCount be 2. Otherwise, letdigitCount be 1. - Letdigits be the
substring oftemplateRemainder from 1 to 1 +digitCount. - Letindex be
ℝ (StringToNumber (digits)). Assert : 0 ≤index ≤ 99.- LetcaptureLen be the number of elements incaptures.
- Ifindex >captureLen anddigitCount = 2, then
- NOTE: When a two-digit replacement pattern specifies an index exceeding the count of capturing groups, it is treated as a one-digit replacement pattern followed by a literal digit.
- SetdigitCount to 1.
- Setdigits to the
substring ofdigits from 0 to 1. - Setindex to
ℝ (StringToNumber (digits)).
- Letref be the
substring oftemplateRemainder from 0 to 1 +digitCount. - If 1 ≤index ≤captureLen, then
- Letcapture becaptures[index - 1].
- Ifcapture is
undefined , then- LetrefReplacement be the empty String.
- Else,
- LetrefReplacement becapture.
- Else,
- LetrefReplacement beref.
- IftemplateRemainder starts with
- Else iftemplateRemainder starts with
"$<" , then- LetgtPos be
StringIndexOf (templateRemainder,">" , 0). - IfgtPos = -1 ornamedCaptures is
undefined , then- Letref be
"$<" . - LetrefReplacement beref.
- Letref be
- Else,
- Letref be the
substring oftemplateRemainder from 0 togtPos + 1. - LetgroupName be the
substring oftemplateRemainder from 2 togtPos. Assert :namedCapturesis an Object .- Letcapture be ?
Get (namedCaptures,groupName). - Ifcapture is
undefined , then- LetrefReplacement be the empty String.
- Else,
- LetrefReplacement be ?
ToString (capture).
- LetrefReplacement be ?
- Letref be the
- LetgtPos be
- Else,
- Letref be the
substring oftemplateRemainder from 0 to 1. - LetrefReplacement beref.
- Letref be the
- LetrefLength be the length ofref.
- SettemplateRemainder to the
substring oftemplateRemainder fromrefLength. - Setresult to the
string-concatenation ofresult andrefReplacement.
- Returnresult.
22.1.3.20 String.prototype.replaceAll (searchValue,replaceValue )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - IfsearchValue is neither
undefined nornull , then- LetisRegExp be ?
IsRegExp (searchValue). - IfisRegExp is
true , then- Letflags be ?
Get (searchValue,"flags" ). - Perform ?
RequireObjectCoercible (flags). - If ?
ToString (flags) does not contain"g" , throw aTypeError exception.
- Letflags be ?
- Letreplacer be ?
GetMethod (searchValue,@@replace ). - Ifreplacer is not
undefined , then- Return ?
Call (replacer,searchValue, «O,replaceValue »).
- Return ?
- LetisRegExp be ?
- Letstring be ?
ToString (O). - LetsearchString be ?
ToString (searchValue). - LetfunctionalReplace be
IsCallable (replaceValue). - IffunctionalReplace is
false , then- SetreplaceValue to ?
ToString (replaceValue).
- SetreplaceValue to ?
- LetsearchLength be the length ofsearchString.
- LetadvanceBy be
max (1,searchLength). - LetmatchPositions be a new empty
List . - Letposition be
StringIndexOf (string,searchString, 0). - Repeat, whileposition ≠ -1,
- Appendposition tomatchPositions.
- Setposition to
StringIndexOf (string,searchString,position +advanceBy).
- LetendOfLastMatch be 0.
- Letresult be the empty String.
- For each elementp ofmatchPositions, do
- Letpreserved be the
substring ofstring fromendOfLastMatch top. - IffunctionalReplace is
true , then - Else,
Assert :replaceValueis a String .- Letcaptures be a new empty
List . - Letreplacement be !
GetSubstitution (searchString,string,p,captures,undefined ,replaceValue).
- Setresult to the
string-concatenation ofresult,preserved, andreplacement. - SetendOfLastMatch top +searchLength.
- Letpreserved be the
- IfendOfLastMatch < the length ofstring, then
- Setresult to the
string-concatenation ofresult and thesubstring ofstring fromendOfLastMatch.
- Setresult to the
- Returnresult.
22.1.3.21 String.prototype.search (regexp )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Ifregexp is neither
undefined nornull , then - Letstring be ?
ToString (O). - Letrx be ?
RegExpCreate (regexp,undefined ). - Return ?
Invoke (rx,@@search , «string »).
This method is intentionally generic; it does not require that its
22.1.3.22 String.prototype.slice (start,end )
This method returns a
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letlen be the length ofS.
- LetintStart be ?
ToIntegerOrInfinity (start). - IfintStart = -∞, letfrom be 0.
- Else ifintStart < 0, letfrom be
max (len +intStart, 0). - Else, letfrom be
min (intStart,len). - Ifend is
undefined , letintEnd belen; else letintEnd be ?ToIntegerOrInfinity (end). - IfintEnd = -∞, letto be 0.
- Else ifintEnd < 0, letto be
max (len +intEnd, 0). - Else, letto be
min (intEnd,len). - Iffrom ≥to, return the empty String.
- Return the
substring ofS fromfrom toto.
This method is intentionally generic; it does not require that its
22.1.3.23 String.prototype.split (separator,limit )
This method returns an Array into which substrings of the result of converting this object to a String have been stored. The substrings are determined by searching from left to right for occurrences ofseparator; these occurrences are not part of any String in the returned array, but serve to divide up the String value. The value ofseparator may be a String of any length or it may be an object, such as a RegExp, that has a
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Ifseparator is neither
undefined nornull , then - LetS be ?
ToString (O). - Iflimit is
undefined , letlim be 232 - 1; else letlim beℝ (?ToUint32 (limit)). - LetR be ?
ToString (separator). - Iflim = 0, then
- Return
CreateArrayFromList (« »).
- Return
- Ifseparator is
undefined , then- Return
CreateArrayFromList («S »).
- Return
- LetseparatorLength be the length ofR.
- IfseparatorLength = 0, then
- Lethead be the
substring ofS from 0 tolim. - LetcodeUnits be a
List consisting of the sequence of code units that are the elements ofhead. - Return
CreateArrayFromList (codeUnits).
- Lethead be the
- IfS is the empty String, return
CreateArrayFromList («S »). - Letsubstrings be a new empty
List . - Leti be 0.
- Letj be
StringIndexOf (S,R, 0). - Repeat, whilej ≠ -1,
- LetT be the
substring ofS fromi toj. - AppendT tosubstrings.
- If the number of elements insubstrings islim, return
CreateArrayFromList (substrings). - Seti toj +separatorLength.
- Setj to
StringIndexOf (S,R,i).
- LetT be the
- LetT be the
substring ofS fromi. - AppendT tosubstrings.
- Return
CreateArrayFromList (substrings).
The value ofseparator may be an empty String. In this case,separator does not match the empty
If the
Ifseparator is
This method is intentionally generic; it does not require that its
22.1.3.24 String.prototype.startsWith (searchString [ ,position ] )
This method performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetisRegExp be ?
IsRegExp (searchString). - IfisRegExp is
true , throw aTypeError exception. - LetsearchStr be ?
ToString (searchString). - Letlen be the length ofS.
- Ifposition is
undefined , letpos be 0; else letpos be ?ToIntegerOrInfinity (position). - Letstart be the result of
clamping pos between 0 andlen. - LetsearchLength be the length ofsearchStr.
- IfsearchLength = 0, return
true . - Letend bestart +searchLength.
- Ifend >len, return
false . - Letsubstring be the
substring ofS fromstart toend. - Ifsubstring issearchStr, return
true . - Return
false .
This method returns
Throwing an exception if the first argument is a RegExp is specified in order to allow future editions to define extensions that allow such argument values.
This method is intentionally generic; it does not require that its
22.1.3.25 String.prototype.substring (start,end )
This method returns a
If either argument is
Ifstart is strictly greater thanend, they are swapped.
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letlen be the length ofS.
- LetintStart be ?
ToIntegerOrInfinity (start). - Ifend is
undefined , letintEnd belen; else letintEnd be ?ToIntegerOrInfinity (end). - LetfinalStart be the result of
clamping intStart between 0 andlen. - LetfinalEnd be the result of
clamping intEnd between 0 andlen. - Letfrom be
min (finalStart,finalEnd). - Letto be
max (finalStart,finalEnd). - Return the
substring ofS fromfrom toto.
This method is intentionally generic; it does not require that its
22.1.3.26 String.prototype.toLocaleLowerCase ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same astoLowerCase except that it is intended to yield a locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.27 String.prototype.toLocaleUpperCase ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used:
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It works exactly the same astoUpperCase except that it is intended to yield a locale-sensitive result corresponding with conventions of the
The meaning of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method is intentionally generic; it does not require that its
22.1.3.28 String.prototype.toLowerCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetsText be
StringToCodePoints (S). - LetlowerText be the result of toLowercase(sText), according to the Unicode Default Case Conversion algorithm.
- LetL be
CodePointsToString (lowerText). - ReturnL.
The result must be derived according to the locale-insensitive case mappings in the Unicode Character Database (this explicitly includes not only the fileUnicodeData.txt, but also all locale-insensitive mappings in the fileSpecialCasing.txt that accompanies it).
The case mapping of some code points may produce multiple code points. In this case the result String may not be the same length as the source String. Because bothtoUpperCase andtoLowerCase have context-sensitive behaviour, the methods are not symmetrical. In other words,s.toUpperCase().toLowerCase() is not necessarily equal tos.toLowerCase().
This method is intentionally generic; it does not require that its
22.1.3.29 String.prototype.toString ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
For a String object, this method happens to return the same thing as thevalueOf method.
22.1.3.30 String.prototype.toUpperCase ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It behaves in exactly the same way asString.prototype.toLowerCase, except that the String is mapped using the toUppercase algorithm of the Unicode Default Case Conversion.
This method is intentionally generic; it does not require that its
22.1.3.31 String.prototype.toWellFormed ( )
This method returns a String representation of this object with all
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - LetstrLen be the length ofS.
- Letk be 0.
- Letresult be the empty String.
- Repeat, whilek <strLen,
- Letcp be
CodePointAt (S,k). - Ifcp.[[IsUnpairedSurrogate]] is
true , then- Setresult to the
string-concatenation ofresult and 0xFFFD (REPLACEMENT CHARACTER).
- Setresult to the
- Else,
- Setresult to the
string-concatenation ofresult andUTF16EncodeCodePoint (cp.[[CodePoint]]).
- Setresult to the
- Setk tok +cp.[[CodeUnitCount]].
- Letcp be
- Returnresult.
22.1.3.32 String.prototype.trim ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- LetS be the
this value. - Return ?
TrimString (S,start+end ).
This method is intentionally generic; it does not require that its
22.1.3.32.1 TrimString (string,where )
The abstract operation TrimString takes argumentsstring (an
- Letstr be ?
RequireObjectCoercible (string). - LetS be ?
ToString (str). - Ifwhere is
start , then- LetT be the String value that is a copy ofS with leading white space removed.
- Else ifwhere is
end , then- LetT be the String value that is a copy ofS with trailing white space removed.
- Else,
Assert :where isstart+end .- LetT be the String value that is a copy ofS with both leading and trailing white space removed.
- ReturnT.
The definition of white space is the union of
22.1.3.33 String.prototype.trimEnd ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- LetS be the
this value. - Return ?
TrimString (S,end ).
This method is intentionally generic; it does not require that its
22.1.3.34 String.prototype.trimStart ( )
This method interprets a String value as a sequence of UTF-16 encoded code points, as described in
It performs the following steps when called:
- LetS be the
this value. - Return ?
TrimString (S,start ).
This method is intentionally generic; it does not require that its
22.1.3.35 String.prototype.valueOf ( )
This method performs the following steps when called:
- Return ?
ThisStringValue (this value).
22.1.3.35.1 ThisStringValue (value )
The abstract operation ThisStringValue takes argumentvalue (an
- Ifvalue
is a String , returnvalue. - Ifvalue
is an Object andvalue has a[[StringData]] internal slot, then- Lets bevalue.[[StringData]].
Assert :sis a String .- Returns.
- Throw a
TypeError exception.
22.1.3.36 String.prototype [ @@iterator ] ( )
This method returns an Iterator object (
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - Lets be ?
ToString (O). - Letclosure be a new
Abstract Closure with no parameters that capturess and performs the following steps when called:- Letlen be the length ofs.
- Letposition be 0.
- Repeat, whileposition <len,
- Letcp be
CodePointAt (s,position). - LetnextIndex beposition +cp.[[CodeUnitCount]].
- LetresultString be the
substring ofs fromposition tonextIndex. - Setposition tonextIndex.
- Perform ?
GeneratorYield (CreateIterResultObject (resultString,false )).
- Letcp be
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%StringIteratorPrototype%" ,%StringIteratorPrototype% ).
The value of the
22.1.4 Properties of String Instances
String instances are
String instances have a
22.1.4.1 length
The number of elements in the String value represented by this String object.
Once a String object is initialized, this property is unchanging. It has the attributes {[[Writable]]:
22.1.5 String Iterator Objects
A String Iterator is an object, that represents a specific iteration over some specific String instance object. There is not a named
22.1.5.1 The %StringIteratorPrototype% Object
The%StringIteratorPrototype% object:
- has properties that are inherited by all String Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
22.1.5.1.1 %StringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%StringIteratorPrototype%" ).
22.1.5.1.2 %StringIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
22.2 RegExp (Regular Expression) Objects
A RegExp object contains a regular expression and the associated flags.
The form and functionality of regular expressions is modelled after the regular expression facility in the Perl 5 programming language.
22.2.1 Patterns
The RegExp
Syntax
Each\uuu\u
The first two lines here are equivalent to CharacterClass.
A number of productions in this section are given alternative definitions in section
22.2.1.1 Static Semantics: Early Errors
This section is amended in
- It is a Syntax Error if
CountLeftCapturingParensWithin (Pattern ) ≥ 232 - 1. - It is a Syntax Error if
Pattern contains two or moreGroupSpecifier s for whichCapturingGroupName ofGroupSpecifier is the same.
- It is a Syntax Error if the MV of the first
DecimalDigits is strictly greater than the MV of the secondDecimalDigits .
- It is a Syntax Error if
GroupSpecifiersThatMatch (GroupName ) is empty.
- It is a Syntax Error if the
CapturingGroupNumber ofDecimalEscape is strictly greater thanCountLeftCapturingParensWithin (thePattern containingAtomEscape ).
- It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue . - It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
- It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue . - It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
- It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierStartChar lexical grammar production.
- It is a Syntax Error if
RegExpIdentifierCodePoint ofRegExpIdentifierStart is not matched by theUnicodeIDStart lexical grammar production.
- It is a Syntax Error if the
CharacterValue ofRegExpUnicodeEscapeSequence is not the numeric value of some code point matched by theIdentifierPartChar lexical grammar production.
- It is a Syntax Error if
RegExpIdentifierCodePoint ofRegExpIdentifierPart is not matched by theUnicodeIDContinue lexical grammar production.
- It is a Syntax Error if the
source text matched by UnicodePropertyName is not a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 . - It is a Syntax Error if the
source text matched by UnicodePropertyValue is not a property value or property value alias for the Unicode property or property alias given by thesource text matched by UnicodePropertyName listed inPropertyValueAliases.txt.
- It is a Syntax Error if the
source text matched by LoneUnicodePropertyNameOrValue is not a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, nor a binary property or binary property alias listed in the “Property name and aliases” column ofTable 68 , nor a binary property of strings listed in the “Property name ” column ofTable 69 . - It is a Syntax Error if the enclosing
Pattern does not have a[UnicodeSetsMode] parameter and thesource text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 69 .
- It is a Syntax Error if
MayContainStrings of theUnicodePropertyValueExpression istrue .
- It is a Syntax Error if
MayContainStrings of theClassContents istrue .
- It is a Syntax Error if
MayContainStrings of theClassContents istrue .
- It is a Syntax Error if the
CharacterValue of the firstClassSetCharacter is strictly greater than theCharacterValue of the secondClassSetCharacter .
22.2.1.2 Static Semantics: CountLeftCapturingParensWithin (node )
The abstract operation CountLeftCapturingParensWithin takes argumentnode (a( pattern character that is matched by the( terminal of the
This section is amended in
It performs the following steps when called:
Assert :node is an instance of a production inthe RegExp Pattern grammar .- Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained withinnode.
22.2.1.3 Static Semantics: CountLeftCapturingParensBefore (node )
The abstract operation CountLeftCapturingParensBefore takes argumentnode (a
This section is amended in
It performs the following steps when called:
Assert :node is an instance of a production inthe RegExp Pattern grammar .- Letpattern be the
Pattern containingnode. - Return the number of
Atom :: ( GroupSpecifier opt Disjunction ) Parse Nodes contained withinpattern that either occur beforenode or containnode.
22.2.1.4 Static Semantics: CapturingGroupNumber
The
This section is amended in
It is defined piecewise over the following productions:
- Return the MV of
NonZeroDigit .
- Letn be the number of code points in
DecimalDigits . - Return (the MV of
NonZeroDigit × 10n plus the MV ofDecimalDigits ).
The definitions of “the MV of
22.2.1.5 Static Semantics: IsCharacterClass
The
This section is amended in
It is defined piecewise over the following productions:
- Return
false .
- Return
true .
22.2.1.6 Static Semantics: CharacterValue
The
This section is amended in
It is defined piecewise over the following productions:
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Letch be the code point matched by
SourceCharacter . - Return the numeric value ofch.
- Return the numeric value of U+0008 (BACKSPACE).
- Return the numeric value of U+002D (HYPHEN-MINUS).
- Return the numeric value according to
Table 65 .
| ControlEscape | Numeric Value | Code Point | Unicode Name | Symbol |
|---|---|---|---|---|
t | 9 | U+0009 | CHARACTER TABULATION | <HT> |
n | 10 | U+000A | LINE FEED (LF) | <LF> |
v | 11 | U+000B | LINE TABULATION | <VT> |
f | 12 | U+000C | FORM FEED (FF) | <FF> |
r | 13 | U+000D | CARRIAGE RETURN (CR) | <CR> |
- Letch be the code point matched by
AsciiLetter . - Leti be the numeric value ofch.
- Return the remainder of dividingi by 32.
- Return the numeric value of U+0000 (NULL).
\0 represents the <NUL> character and cannot be followed by a decimal digit.
- Return the MV of
HexEscapeSequence .
- Letlead be the
CharacterValue ofHexLeadSurrogate . - Lettrail be the
CharacterValue ofHexTrailSurrogate . - Letcp be
UTF16SurrogatePairToCodePoint (lead,trail). - Return the numeric value ofcp.
- Return the MV of
Hex4Digits .
- Return the MV of
CodePoint .
- Return the MV of
Hex4Digits .
- Letch be the code point matched by
IdentityEscape . - Return the numeric value ofch.
- Letch be the code point matched by
SourceCharacter . - Return the numeric value ofch.
- Letch be the code point matched by
ClassSetReservedPunctuator . - Return the numeric value ofch.
- Return the numeric value of U+0008 (BACKSPACE).
22.2.1.7 Static Semantics: MayContainStrings
The
- Return
false .
- If the
source text matched by LoneUnicodePropertyNameOrValue is a binary property of strings listed in the “Property name ” column ofTable 69 , returntrue . - Return
false .
- If the
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of theClassSetOperand istrue , returntrue . - If
ClassUnion is present, returnMayContainStrings of theClassUnion . - Return
false .
- If
MayContainStrings of the firstClassSetOperand isfalse , returnfalse . - If
MayContainStrings of the secondClassSetOperand isfalse , returnfalse . - Return
true .
- If
MayContainStrings of theClassIntersection isfalse , returnfalse . - If
MayContainStrings of theClassSetOperand isfalse , returnfalse . - Return
true .
- Return
MayContainStrings of the firstClassSetOperand .
- Return
MayContainStrings of theClassSubtraction .
- If
MayContainStrings of theClassString istrue , returntrue . - Return
MayContainStrings of theClassStringDisjunctionContents .
- Return
true .
- Return
MayContainStrings of theNonEmptyClassString .
- If
NonEmptyClassString is present, returntrue . - Return
false .
22.2.1.8 Static Semantics: GroupSpecifiersThatMatch (thisGroupName )
The abstract operation GroupSpecifiersThatMatch takes argumentthisGroupName (a
- Letname be the
CapturingGroupName ofthisGroupName. - Letpattern be the
Pattern containingthisGroupName. - Letresult be a new empty
List . - For each
GroupSpecifier gs thatpattern contains, do- If the
CapturingGroupName ofgs isname, then- Appendgs toresult.
- If the
- Returnresult.
22.2.1.9 Static Semantics: CapturingGroupName
The
- LetidTextUnescaped be
RegExpIdentifierCodePoints ofRegExpIdentifierName . - Return
CodePointsToString (idTextUnescaped).
22.2.1.10 Static Semantics: RegExpIdentifierCodePoints
The
- Letcp be
RegExpIdentifierCodePoint ofRegExpIdentifierStart . - Return «cp ».
- Letcps be
RegExpIdentifierCodePoints of the derivedRegExpIdentifierName . - Letcp be
RegExpIdentifierCodePoint ofRegExpIdentifierPart . - Return the
list-concatenation ofcps and «cp ».
22.2.1.11 Static Semantics: RegExpIdentifierCodePoint
The
- Return the code point matched by
IdentifierStartChar .
- Return the code point matched by
IdentifierPartChar .
- Return the code point whose numeric value is the
CharacterValue ofRegExpUnicodeEscapeSequence .
- Letlead be the code unit whose numeric value is the numeric value of the code point matched by
UnicodeLeadSurrogate . - Lettrail be the code unit whose numeric value is the numeric value of the code point matched by
UnicodeTrailSurrogate . - Return
UTF16SurrogatePairToCodePoint (lead,trail).
22.2.2 Pattern Semantics
A regular expression pattern is converted into an
Au nor av. Otherwise, it is a Unicode pattern. A BMP pattern matches against a String interpreted as consisting of a sequence of 16-bit values that are Unicode code points in the range of the Basic Multilingual Plane. A Unicode pattern matches against a String interpreted as consisting of Unicode code points encoded using UTF-16. In the context of describing the behaviour of a BMP pattern “character” means a single 16-bit Unicode BMP code point. In the context of describing the behaviour of a Unicode pattern “character” means a UTF-16 encoded code point (
The syntax and semantics of
For example, consider a pattern expressed in source text as the single non-BMP character U+1D11E (MUSICAL SYMBOL G CLEF). Interpreted as a Unicode pattern, it would be a single element (character)
Patterns are passed to the RegExp
An implementation may not actually perform such translations to or from UTF-16, but the semantics of this specification requires that the result of pattern matching be as if such translations were performed.
22.2.2.1 Notation
The descriptions below use the following internal data structures:
- ACharSetElement is one of the two following entities:
- Ifrer.[[UnicodeSets]] is
false , then a CharSetElement is a character in the sense of the Pattern Semantics above. - Ifrer.[[UnicodeSets]] is
true , then a CharSetElement is a sequence whose elements are characters in the sense of the Pattern Semantics above. This includes the empty sequence, sequences of one character, and sequences of more than one character. For convenience, when working with CharSetElements of this kind, an individual character is treated interchangeably with a sequence of one character.
- Ifrer.[[UnicodeSets]] is
- ACharSet is a mathematical set of CharSetElements.
- ACaptureRange is a
Record {[[StartIndex]],[[EndIndex]] } that represents the range of characters included in a capture, where[[StartIndex]] is aninteger representing the start index (inclusive) of the range withinInput, and[[EndIndex]] is aninteger representing the end index (exclusive) of the range withinInput. For anyCaptureRange , these indices must satisfy the invariant that[[StartIndex]] ≤[[EndIndex]]. - AMatchState is a
Record {[[Input]],[[EndIndex]],[[Captures]] } where[[Input]] is aList of characters representing the String being matched,[[EndIndex]] is aninteger , and[[Captures]] is aList of values, one for eachleft-capturing parenthesis in the pattern. States are used to represent partial match states in the regular expression matching algorithms. The[[EndIndex]] is one plus the index of the last input character matched so far by the pattern, while[[Captures]] holds the results of capturing parentheses. Thenth element of[[Captures]] is either aCaptureRange representing the range of characters captured by thenth set of capturing parentheses, orundefined if thenth set of capturing parentheses hasn't been reached yet. Due to backtracking, many States may be in use at any time during the matching process. - AMatchResult is either a
MatchState or the special tokenfailure that indicates that the match failed. - AMatcherContinuation is an
Abstract Closure that takes oneMatchState argument and returns aMatchResult result. TheMatcherContinuation attempts to match the remaining portion (specified by the closure's captured values) of the pattern againstInput, starting at the intermediate state given by itsMatchState argument. If the match succeeds, theMatcherContinuation returns the finalMatchState that it reached; if the match fails, theMatcherContinuation returnsfailure . - AMatcher is an
Abstract Closure that takes two arguments—aMatchState and aMatcherContinuation —and returns aMatchResult result. AMatcher attempts to match a middle subpattern (specified by the closure's captured values) of the pattern against theMatchState 's[[Input]], starting at the intermediate state given by itsMatchState argument. TheMatcherContinuation argument should be a closure that matches the rest of the pattern. After matching the subpattern of a pattern to obtain a newMatchState , theMatcher then callsMatcherContinuation on that newMatchState to test if the rest of the pattern can match as well. If it can, theMatcher returns theMatchState returned byMatcherContinuation ; if not, theMatcher may try different choices at its choice points, repeatedly callingMatcherContinuation until it either succeeds or all possibilities have been exhausted.
22.2.2.1.1 RegExp Records
ARegExp Record is a
It has the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[IgnoreCase]] | a Boolean | indicates whether |
| [[Multiline]] | a Boolean | indicates whether |
| [[DotAll]] | a Boolean | indicates whether |
| [[Unicode]] | a Boolean | indicates whether |
| [[UnicodeSets]] | a Boolean | indicates whether |
| [[CapturingGroupsCount]] | a non-negative | the number of |
22.2.2.2 Runtime Semantics: CompilePattern
The
- Letm be
CompileSubpattern ofDisjunction with argumentsrer andforward . - Return a new
Abstract Closure with parameters (Input,index) that capturesrer andm and performs the following steps when called:Assert :Input is aList of characters.Assert : 0 ≤index ≤ the number of elements inInput.- Letc be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert :y is aMatchState .- Returny.
- Letcap be a
List ofrer.[[CapturingGroupsCount]]undefined values, indexed 1 throughrer.[[CapturingGroupsCount]]. - Letx be the
MatchState {[[Input]]:Input,[[EndIndex]]:index,[[Captures]]:cap }. - Returnm(x,c).
A Pattern compiles to an
22.2.2.3 Runtime Semantics: CompileSubpattern
The
This section is amended in
It is defined piecewise over the following productions:
- Letm1 be
CompileSubpattern ofAlternative with argumentsrer anddirection. - Letm2 be
CompileSubpattern ofDisjunction with argumentsrer anddirection. - Return
MatchTwoAlternatives (m1,m2).
The| regular expression operator separates two alternatives. The pattern first tries to match the left| produce
/a|ab/.exec("abc")returns the result
/((a)|(ab))((c)|(bc))/.exec("abc")returns the array
["abc","a","a",undefined,"bc",undefined,"bc"]and not
["abc","ab",undefined,"ab","c","c",undefined]The order in which the two alternatives are tried is independent of the value ofdirection.
- Return
EmptyMatcher ().
- Letm1 be
CompileSubpattern ofAlternative with argumentsrer anddirection. - Letm2 be
CompileSubpattern ofTerm with argumentsrer anddirection. - Return
MatchSequence (m1,m2,direction).
Consecutive
- Return
CompileAssertion ofAssertion with argumentrer.
The resulting
- Return
CompileAtom ofAtom with argumentsrer anddirection.
- Letm be
CompileAtom ofAtom with argumentsrer anddirection. - Letq be
CompileQuantifier ofQuantifier . Assert :q.[[Min]] ≤q.[[Max]].- LetparenIndex be
CountLeftCapturingParensBefore (Term ). - LetparenCount be
CountLeftCapturingParensWithin (Atom ). - Return a new
Matcher with parameters (x,c) that capturesm,q,parenIndex, andparenCount and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Return
RepeatMatcher (m,q.[[Min]],q.[[Max]],q.[[Greedy]],x,c,parenIndex,parenCount).
22.2.2.3.1 RepeatMatcher (m,min,max,greedy,x,c,parenIndex,parenCount )
The abstract operation RepeatMatcher takes argumentsm (a
- Ifmax = 0, returnc(x).
- Letd be a new
MatcherContinuation with parameters (y) that capturesm,min,max,greedy,x,c,parenIndex, andparenCount and performs the following steps when called:Assert :y is aMatchState .- Ifmin = 0 andy.[[EndIndex]] =x.[[EndIndex]], return
failure . - Ifmin = 0, letmin2 be 0; otherwise letmin2 bemin - 1.
- Ifmax = +∞, letmax2 be +∞; otherwise letmax2 bemax - 1.
- Return
RepeatMatcher (m,min2,max2,greedy,y,c,parenIndex,parenCount).
- Letcap be a copy ofx.[[Captures]].
- For each
integer k in theinclusive interval fromparenIndex + 1 toparenIndex +parenCount, setcap[k] toundefined . - LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- Letxr be the
MatchState {[[Input]]:Input,[[EndIndex]]:e,[[Captures]]:cap }. - Ifmin ≠ 0, returnm(xr,d).
- Ifgreedy is
false , then- Letz bec(x).
- Ifz is not
failure , returnz. - Returnm(xr,d).
- Letz bem(xr,d).
- Ifz is not
failure , returnz. - Returnc(x).
An
If the
Compare
/a[a-z]{2,4}/.exec("abcdefghi")which returns
/a[a-z]{2,4}?/.exec("abcdefghi")which returns
Consider also
/(aa|aabaac|ba|b|c)*/.exec("aabaac")which, by the choice point ordering above, returns the array
["aaba","ba"]and not any of:
["aabaac","aabaac"]["aabaac","c"]The above ordering of choice points can be used to write a regular expression that calculates the greatest common divisor of two numbers (represented in unary notation). The following example calculates the gcd of 10 and 15:
"aaaaaaaaaa,aaaaaaaaaaaaaaa".replace(/^(a+)\1*,\1+$/,"$1")which returns the gcd in unary notation
Step
/(z)((a+)?(b+)?(c))*/.exec("zaacbbbcac")which returns the array
["zaacbbbcac","z","ac","a",undefined,"c"]and not
["zaacbbbcac","z","ac","a","bbb","c"]because each iteration of the outermost* clears all captured Strings contained in the quantified
Step
/(a*)*/.exec("b")or the slightly more complicated:
/(a*)b\1+/.exec("baaaac")which returns the array
["b",""]22.2.2.3.2 EmptyMatcher ( )
The abstract operation EmptyMatcher takes no arguments and returns a
- Return a new
Matcher with parameters (x,c) that captures nothing and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Returnc(x).
22.2.2.3.3 MatchTwoAlternatives (m1,m2 )
The abstract operation MatchTwoAlternatives takes argumentsm1 (a
- Return a new
Matcher with parameters (x,c) that capturesm1 andm2 and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letr bem1(x,c).
- Ifr is not
failure , returnr. - Returnm2(x,c).
22.2.2.3.4 MatchSequence (m1,m2,direction )
The abstract operation MatchSequence takes argumentsm1 (a
- Ifdirection is
forward , then- Return a new
Matcher with parameters (x,c) that capturesm1 andm2 and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that capturesc andm2 and performs the following steps when called:Assert :y is aMatchState .- Returnm2(y,c).
- Returnm1(x,d).
- Return a new
- Else,
Assert :direction isbackward .- Return a new
Matcher with parameters (x,c) that capturesm1 andm2 and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that capturesc andm1 and performs the following steps when called:Assert :y is aMatchState .- Returnm1(y,c).
- Returnm2(x,d).
22.2.2.4 Runtime Semantics: CompileAssertion
The
This section is amended in
It is defined piecewise over the following productions:
- Return a new
Matcher with parameters (x,c) that capturesrer and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- Ife = 0, or ifrer.[[Multiline]] is
true and the characterInput[e - 1] is matched byLineTerminator , then- Returnc(x).
- Return
failure .
Even when they flag is used with a pattern,^ always matches only at the beginning ofInput, or (ifrer.[[Multiline]] is
- Return a new
Matcher with parameters (x,c) that capturesrer and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- LetInputLength be the number of elements inInput.
- Ife =InputLength, or ifrer.[[Multiline]] is
true and the characterInput[e] is matched byLineTerminator , then- Returnc(x).
- Return
failure .
- Return a new
Matcher with parameters (x,c) that capturesrer and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- Leta be
IsWordChar (rer,Input,e - 1). - Letb be
IsWordChar (rer,Input,e). - Ifa is
true andb isfalse , or ifa isfalse andb istrue , returnc(x). - Return
failure .
- Return a new
Matcher with parameters (x,c) that capturesrer and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- Leta be
IsWordChar (rer,Input,e - 1). - Letb be
IsWordChar (rer,Input,e). - Ifa is
true andb istrue , or ifa isfalse andb isfalse , returnc(x). - Return
failure .
- Letm be
CompileSubpattern ofDisjunction with argumentsrer andforward . - Return a new
Matcher with parameters (x,c) that capturesm and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert :y is aMatchState .- Returny.
- Letr bem(x,d).
- Ifr is
failure , returnfailure . Assert :r is aMatchState .- Letcap ber.[[Captures]].
- LetInput bex.[[Input]].
- Letxe bex.[[EndIndex]].
- Letz be the
MatchState {[[Input]]:Input,[[EndIndex]]:xe,[[Captures]]:cap }. - Returnc(z).
The form(?=) specifies a zero-width positive lookahead. In order for it to succeed, the pattern inside(?= form (this unusual behaviour is inherited from Perl). This only matters when the
For example,
/(?=(a+))/.exec("baaabac")matches the empty String immediately after the firstb and therefore returns the array:
["","aaa"]To illustrate the lack of backtracking into the lookahead, consider:
/(?=(a+))a*b\1/.exec("baaabac")This expression returns
["aba","a"]and not:
["aaaba","a"]- Letm be
CompileSubpattern ofDisjunction with argumentsrer andforward . - Return a new
Matcher with parameters (x,c) that capturesm and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert :y is aMatchState .- Returny.
- Letr bem(x,d).
- Ifr is not
failure , returnfailure . - Returnc(x).
The form(?!) specifies a zero-width negative lookahead. In order for it to succeed, the pattern inside
/(.*?)a(?!(a+)b\2c)\2(.*)/.exec("baaabaac")looks for ana not immediately followed by some positive number n ofa's, ab, another na's (specified by the first\2) and ac. The second\2 is outside the negative lookahead, so it matches against
["baaabaac","ba",undefined,"abaac"]- Letm be
CompileSubpattern ofDisjunction with argumentsrer andbackward . - Return a new
Matcher with parameters (x,c) that capturesm and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert :y is aMatchState .- Returny.
- Letr bem(x,d).
- Ifr is
failure , returnfailure . Assert :r is aMatchState .- Letcap ber.[[Captures]].
- LetInput bex.[[Input]].
- Letxe bex.[[EndIndex]].
- Letz be the
MatchState {[[Input]]:Input,[[EndIndex]]:xe,[[Captures]]:cap }. - Returnc(z).
- Letm be
CompileSubpattern ofDisjunction with argumentsrer andbackward . - Return a new
Matcher with parameters (x,c) that capturesm and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that captures nothing and performs the following steps when called:Assert :y is aMatchState .- Returny.
- Letr bem(x,d).
- Ifr is not
failure , returnfailure . - Returnc(x).
22.2.2.4.1 IsWordChar (rer,Input,e )
The abstract operation IsWordChar takes argumentsrer (a
- LetInputLength be the number of elements inInput.
- Ife = -1 ore =InputLength, return
false . - Letc be the characterInput[e].
- If
WordCharacters (rer) containsc, returntrue . - Return
false .
22.2.2.5 Runtime Semantics: CompileQuantifier
The
- Letqp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record {[[Min]]:qp.[[Min]],[[Max]]:qp.[[Max]],[[Greedy]]:true }.
- Letqp be
CompileQuantifierPrefix ofQuantifierPrefix . - Return the
Record {[[Min]]:qp.[[Min]],[[Max]]:qp.[[Max]],[[Greedy]]:false }.
22.2.2.6 Runtime Semantics: CompileQuantifierPrefix
The
- Return the
Record {[[Min]]: 0,[[Max]]: +∞ }.
- Return the
Record {[[Min]]: 1,[[Max]]: +∞ }.
- Return the
Record {[[Min]]: 0,[[Max]]: 1 }.
- Leti be the MV of
DecimalDigits (see12.9.3 ). - Return the
Record {[[Min]]:i,[[Max]]:i }.
- Leti be the MV of
DecimalDigits . - Return the
Record {[[Min]]:i,[[Max]]: +∞ }.
- Leti be the MV of the first
DecimalDigits . - Letj be the MV of the second
DecimalDigits . - Return the
Record {[[Min]]:i,[[Max]]:j }.
22.2.2.7 Runtime Semantics: CompileAtom
The
This section is amended in
It is defined piecewise over the following productions:
- Letch be the character matched by
PatternCharacter . - LetA be a one-element
CharSet containing the characterch. - Return
CharacterSetMatcher (rer,A,false ,direction).
- LetA be
AllCharacters (rer). - Ifrer.[[DotAll]] is not
true , then- Remove fromA all characters corresponding to a code point on the right-hand side of the
LineTerminator production.
- Remove fromA all characters corresponding to a code point on the right-hand side of the
- Return
CharacterSetMatcher (rer,A,false ,direction).
- Letcc be
CompileCharacterClass ofCharacterClass with argumentrer. - Letcs becc.[[CharSet]].
- Ifrer.[[UnicodeSets]] is
false , or if everyCharSetElement ofcs consists of a single character (including ifcs is empty), returnCharacterSetMatcher (rer,cs,cc.[[Invert]],direction). Assert :cc.[[Invert]] isfalse .- Letlm be an empty
List ofMatchers . - For each
CharSetElement s incs containing more than 1 character, iterating in descending order of length, do- Letcs2 be a one-element
CharSet containing the last code point ofs. - Letm2 be
CharacterSetMatcher (rer,cs2,false ,direction). - For each code pointc1 ins, iterating backwards from its second-to-last code point, do
- Letcs1 be a one-element
CharSet containingc1. - Letm1 be
CharacterSetMatcher (rer,cs1,false ,direction). - Setm2 to
MatchSequence (m1,m2,direction).
- Letcs1 be a one-element
- Appendm2 tolm.
- Letcs2 be a one-element
- Letsingles be the
CharSet containing everyCharSetElement ofcs that consists of a single character. - Append
CharacterSetMatcher (rer,singles,false ,direction) tolm. - Ifcs contains the empty sequence of characters, append
EmptyMatcher () tolm. - Letm2 be the last
Matcher inlm. - For each
Matcher m1 oflm, iterating backwards from its second-to-last element, do- Setm2 to
MatchTwoAlternatives (m1,m2).
- Setm2 to
- Returnm2.
- Letm be
CompileSubpattern ofDisjunction with argumentsrer anddirection. - LetparenIndex be
CountLeftCapturingParensBefore (Atom ). - Return a new
Matcher with parameters (x,c) that capturesdirection,m, andparenIndex and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- Letd be a new
MatcherContinuation with parameters (y) that capturesx,c,direction, andparenIndex and performs the following steps when called:Assert :y is aMatchState .- Letcap be a copy ofy.[[Captures]].
- LetInput bex.[[Input]].
- Letxe bex.[[EndIndex]].
- Letye bey.[[EndIndex]].
- Ifdirection is
forward , thenAssert :xe ≤ye.- Letr be the
CaptureRange {[[StartIndex]]:xe,[[EndIndex]]:ye }.
- Else,
Assert :direction isbackward .Assert :ye ≤xe.- Letr be the
CaptureRange {[[StartIndex]]:ye,[[EndIndex]]:xe }.
- Setcap[parenIndex + 1] tor.
- Letz be the
MatchState {[[Input]]:Input,[[EndIndex]]:ye,[[Captures]]:cap }. - Returnc(z).
- Returnm(x,d).
Parentheses of the form() serve both to group the components of the\ followed by a non-zero decimal number), referenced in a replace String, or returned as part of an array from the regular expression matching(?:) instead.
- Return
CompileSubpattern ofDisjunction with argumentsrer anddirection.
- Letn be the
CapturingGroupNumber ofDecimalEscape . Assert :n ≤rer.[[CapturingGroupsCount]].- Return
BackreferenceMatcher (rer,n,direction).
An escape sequence of the form\ followed by a non-zero decimal numbern matches the result of thenth set of capturing parentheses (
- Letcv be the
CharacterValue ofCharacterEscape . - Letch be the character whose character value iscv.
- LetA be a one-element
CharSet containing the characterch. - Return
CharacterSetMatcher (rer,A,false ,direction).
- Letcs be
CompileToCharSet ofCharacterClassEscape with argumentrer. - Ifrer.[[UnicodeSets]] is
false , or if everyCharSetElement ofcs consists of a single character (including ifcs is empty), returnCharacterSetMatcher (rer,cs,false ,direction). - Letlm be an empty
List ofMatchers . - For each
CharSetElement s incs containing more than 1 character, iterating in descending order of length, do- Letcs2 be a one-element
CharSet containing the last code point ofs. - Letm2 be
CharacterSetMatcher (rer,cs2,false ,direction). - For each code pointc1 ins, iterating backwards from its second-to-last code point, do
- Letcs1 be a one-element
CharSet containingc1. - Letm1 be
CharacterSetMatcher (rer,cs1,false ,direction). - Setm2 to
MatchSequence (m1,m2,direction).
- Letcs1 be a one-element
- Appendm2 tolm.
- Letcs2 be a one-element
- Letsingles be the
CharSet containing everyCharSetElement ofcs that consists of a single character. - Append
CharacterSetMatcher (rer,singles,false ,direction) tolm. - Ifcs contains the empty sequence of characters, append
EmptyMatcher () tolm. - Letm2 be the last
Matcher inlm. - For each
Matcher m1 oflm, iterating backwards from its second-to-last element, do- Setm2 to
MatchTwoAlternatives (m1,m2).
- Setm2 to
- Returnm2.
- LetmatchingGroupSpecifiers be
GroupSpecifiersThatMatch (GroupName ). Assert :matchingGroupSpecifiers contains a singleGroupSpecifier .- LetgroupSpecifier be the sole element ofmatchingGroupSpecifiers.
- LetparenIndex be
CountLeftCapturingParensBefore (groupSpecifier). - Return
BackreferenceMatcher (rer,parenIndex,direction).
22.2.2.7.1 CharacterSetMatcher (rer,A,invert,direction )
The abstract operation CharacterSetMatcher takes argumentsrer (a
- Ifrer.[[UnicodeSets]] is
true , thenAssert :invert isfalse .Assert : EveryCharSetElement ofA consists of a single character.
- Return a new
Matcher with parameters (x,c) that capturesrer,A,invert, anddirection and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Lete bex.[[EndIndex]].
- Ifdirection is
forward , letf bee + 1. - Else, letf bee - 1.
- LetInputLength be the number of elements inInput.
- Iff < 0 orf >InputLength, return
failure . - Letindex be
min (e,f). - Letch be the characterInput[index].
- Letcc be
Canonicalize (rer,ch). - If there exists a
CharSetElement inA containing exactly one charactera such thatCanonicalize (rer,a) iscc, letfound betrue . Otherwise, letfound befalse . - Ifinvert is
false andfound isfalse , returnfailure . - Ifinvert is
true andfound istrue , returnfailure . - Letcap bex.[[Captures]].
- Lety be the
MatchState {[[Input]]:Input,[[EndIndex]]:f,[[Captures]]:cap }. - Returnc(y).
22.2.2.7.2 BackreferenceMatcher (rer,n,direction )
The abstract operation BackreferenceMatcher takes argumentsrer (a
Assert :n ≥ 1.- Return a new
Matcher with parameters (x,c) that capturesrer,n, anddirection and performs the following steps when called:Assert :x is aMatchState .Assert :c is aMatcherContinuation .- LetInput bex.[[Input]].
- Letcap bex.[[Captures]].
- Letr becap[n].
- Ifr is
undefined , returnc(x). - Lete bex.[[EndIndex]].
- Letrs ber.[[StartIndex]].
- Letre ber.[[EndIndex]].
- Letlen bere -rs.
- Ifdirection is
forward , letf bee +len. - Else, letf bee -len.
- LetInputLength be the number of elements inInput.
- Iff < 0 orf >InputLength, return
failure . - Letg be
min (e,f). - If there exists an
integer i in theinterval from 0 (inclusive) tolen (exclusive) such thatCanonicalize (rer,Input[rs +i]) is notCanonicalize (rer,Input[g +i]), returnfailure . - Lety be the
MatchState {[[Input]]:Input,[[EndIndex]]:f,[[Captures]]:cap }. - Returnc(y).
22.2.2.7.3 Canonicalize (rer,ch )
The abstract operation Canonicalize takes argumentsrer (a
- If
HasEitherUnicodeFlag (rer) istrue andrer.[[IgnoreCase]] istrue , then- If the file
CaseFolding.txtof the Unicode Character Database provides a simple or common case folding mapping forch, return the result of applying that mapping toch. - Returnch.
- If the file
- Ifrer.[[IgnoreCase]] is
false , returnch. Assert :ch is a UTF-16 code unit.- Letcp be the code point whose numeric value is the numeric value ofch.
- Letu be the result of toUppercase(«cp »), according to the Unicode Default Case Conversion algorithm.
- LetuStr be
CodePointsToString (u). - If the length ofuStr ≠ 1, returnch.
- Letcu beuStr's single code unit element.
- If the numeric value ofch ≥ 128 and the numeric value ofcu < 128, returnch.
- Returncu.
In case-insignificant matches whenß (U+00DF LATIN SMALL LETTER SHARP S) toss orSS. It may however map code points outside the Basic Latin block to code points within it—for example,ſ (U+017F LATIN SMALL LETTER LONG S) case-folds tos (U+0073 LATIN SMALL LETTER S) andK (U+212A KELVIN SIGN) case-folds tok (U+006B LATIN SMALL LETTER K). Strings containing those code points are matched by regular expressions such as/[a-z]/ui.
In case-insignificant matches whenΩ (U+2126 OHM SIGN) is mapped by toUppercase to itself but by toCasefold toω (U+03C9 GREEK SMALL LETTER OMEGA) along withΩ (U+03A9 GREEK CAPITAL LETTER OMEGA), so/[ω]/ui and/[\u03A9]/ui but not by/[ω]/i or/[\u03A9]/i. Also, no code point outside the Basic Latin block is mapped to a code point within it, so strings such as/[a-z]/i.
22.2.2.8 Runtime Semantics: CompileCharacterClass
The
- LetA be
CompileToCharSet ofClassContents with argumentrer. - Return the
Record {[[CharSet]]:A,[[Invert]]:false }.
- LetA be
CompileToCharSet ofClassContents with argumentrer. - Ifrer.[[UnicodeSets]] is
true , then- Return the
Record {[[CharSet]]:CharacterComplement (rer,A),[[Invert]]:false }.
- Return the
- Return the
Record {[[CharSet]]:A,[[Invert]]:true }.
22.2.2.9 Runtime Semantics: CompileToCharSet
The
This section is amended in
It is defined piecewise over the following productions:
- Return the empty
CharSet .
- LetA be
CompileToCharSet ofClassAtom with argumentrer. - LetB be
CompileToCharSet ofNonemptyClassRangesNoDash with argumentrer. - Return the union of
CharSets A andB.
- LetA be
CompileToCharSet of the firstClassAtom with argumentrer. - LetB be
CompileToCharSet of the secondClassAtom with argumentrer. - LetC be
CompileToCharSet ofClassContents with argumentrer. - LetD be
CharacterRange (A,B). - Return the union ofD andC.
- LetA be
CompileToCharSet ofClassAtomNoDash with argumentrer. - LetB be
CompileToCharSet ofNonemptyClassRangesNoDash with argumentrer. - Return the union of
CharSets A andB.
- LetA be
CompileToCharSet ofClassAtomNoDash with argumentrer. - LetB be
CompileToCharSet ofClassAtom with argumentrer. - LetC be
CompileToCharSet ofClassContents with argumentrer. - LetD be
CharacterRange (A,B). - Return the union ofD andC.
Even if the pattern ignores case, the case of the two ends of a range is significant in determining which characters belong to the range. Thus, for example, the pattern/[E-F]/i matches only the lettersE,F,e, andf, while the pattern/[E-f]/i matches all uppercase and lowercase letters in the Unicode Basic Latin block as well as the symbols[,\,],^,_, and`.
A- character can be treated literally or it can denote a range. It is treated literally if it is the first or last character of
- Return the
CharSet containing the single character-U+002D (HYPHEN-MINUS).
- Return the
CharSet containing the character matched bySourceCharacter .
- Letcv be the
CharacterValue of thisClassEscape . - Letc be the character whose character value iscv.
- Return the
CharSet containing the single characterc.
A\b,\B, and backreferences. Inside a\b means the backspace character, while\B and backreferences raise errors. Using a backreference inside a
- Return the ten-element
CharSet containing the characters0,1,2,3,4,5,6,7,8, and9.
- LetS be the
CharSet returned byCharacterClassEscape :: d - Return
CharacterComplement (rer,S).
- Return the
CharSet containing all characters corresponding to a code point on the right-hand side of theWhiteSpace orLineTerminator productions.
- LetS be the
CharSet returned byCharacterClassEscape :: s - Return
CharacterComplement (rer,S).
- Return
MaybeSimpleCaseFolding (rer,WordCharacters (rer)).
- LetS be the
CharSet returned byCharacterClassEscape :: w - Return
CharacterComplement (rer,S).
- Return
CompileToCharSet ofUnicodePropertyValueExpression with argumentrer.
- LetS be
CompileToCharSet ofUnicodePropertyValueExpression with argumentrer. Assert :S contains only single code points.- Return
CharacterComplement (rer,S).
- Letps be the
source text matched by UnicodePropertyName . - Letp be
UnicodeMatchProperty (rer,ps). Assert :p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 .- Letvs be the
source text matched by UnicodePropertyValue . - Letv be
UnicodeMatchPropertyValue (p,vs). - LetA be the
CharSet containing all Unicode code points whose character database definition includes the propertyp with valuev. - Return
MaybeSimpleCaseFolding (rer,A).
- Lets be the
source text matched by LoneUnicodePropertyNameOrValue . - If
UnicodeMatchPropertyValue (General_Category,s) is a Unicode property value or property value alias for the General_Category (gc) property listed inPropertyValueAliases.txt, then- Return the
CharSet containing all Unicode code points whose character database definition includes the property “General_Category” with values.
- Return the
- Letp be
UnicodeMatchProperty (rer,s). Assert :p is a binary Unicode property or binary property alias listed in the “Property name and aliases” column ofTable 68 , or a binary Unicode property of strings listed in the “Property name ” column ofTable 69 .- LetA be the
CharSet containing all CharSetElements whose character database definition includes the propertyp with value “True”. - Return
MaybeSimpleCaseFolding (rer,A).
- LetA be
CompileToCharSet ofClassSetRange with argumentrer. - If
ClassUnion is present, then- LetB be
CompileToCharSet ofClassUnion with argumentrer. - Return the union of
CharSets A andB.
- LetB be
- ReturnA.
- LetA be
CompileToCharSet ofClassSetOperand with argumentrer. - If
ClassUnion is present, then- LetB be
CompileToCharSet ofClassUnion with argumentrer. - Return the union of
CharSets A andB.
- LetB be
- ReturnA.
- LetA be
CompileToCharSet of the firstClassSetOperand with argumentrer. - LetB be
CompileToCharSet of the secondClassSetOperand with argumentrer. - Return the intersection of
CharSets A andB.
- LetA be
CompileToCharSet of theClassIntersection with argumentrer. - LetB be
CompileToCharSet of theClassSetOperand with argumentrer. - Return the intersection of
CharSets A andB.
- LetA be
CompileToCharSet of the firstClassSetOperand with argumentrer. - LetB be
CompileToCharSet of the secondClassSetOperand with argumentrer. - Return the
CharSet containing the CharSetElements ofA which are not also CharSetElements ofB.
- LetA be
CompileToCharSet of theClassSubtraction with argumentrer. - LetB be
CompileToCharSet of theClassSetOperand with argumentrer. - Return the
CharSet containing the CharSetElements ofA which are not also CharSetElements ofB.
- LetA be
CompileToCharSet of the firstClassSetCharacter with argumentrer. - LetB be
CompileToCharSet of the secondClassSetCharacter with argumentrer. - Return
MaybeSimpleCaseFolding (rer,CharacterRange (A,B)).
The result will often consist of two or more ranges. When UnicodeSets is
- LetA be
CompileToCharSet ofClassSetCharacter with argumentrer. - Return
MaybeSimpleCaseFolding (rer,A).
- LetA be
CompileToCharSet ofClassStringDisjunction with argumentrer. - Return
MaybeSimpleCaseFolding (rer,A).
- Return
CompileToCharSet ofNestedClass with argumentrer.
- Return
CompileToCharSet ofClassContents with argumentrer.
- LetA be
CompileToCharSet ofClassContents with argumentrer. - Return
CharacterComplement (rer,A).
- Return
CompileToCharSet ofCharacterClassEscape with argumentrer.
- Return
CompileToCharSet ofClassStringDisjunctionContents with argumentrer.
- Lets be
CompileClassSetString ofClassString with argumentrer. - Return the
CharSet containing the one strings.
- Lets be
CompileClassSetString ofClassString with argumentrer. - LetA be the
CharSet containing the one strings. - LetB be
CompileToCharSet ofClassStringDisjunctionContents with argumentrer. - Return the union of
CharSets A andB.
- Letcv be the
CharacterValue of thisClassSetCharacter . - Letc be the character whose character value iscv.
- Return the
CharSet containing the single characterc.
- Return the
CharSet containing the single character U+0008 (BACKSPACE).
22.2.2.9.1 CharacterRange (A,B )
The abstract operation CharacterRange takes argumentsA (a
Assert :A andB each contain exactly one character.- Leta be the one character in
CharSet A. - Letb be the one character in
CharSet B. - Leti be the character value of charactera.
- Letj be the character value of characterb.
Assert :i ≤j.- Return the
CharSet containing all characters with a character value in theinclusive interval fromi toj.
22.2.2.9.2 HasEitherUnicodeFlag (rer )
The abstract operation HasEitherUnicodeFlag takes argumentrer (a
- Ifrer.[[Unicode]] is
true orrer.[[UnicodeSets]] istrue , then- Return
true .
- Return
- Return
false .
22.2.2.9.3 WordCharacters (rer )
The abstract operation WordCharacters takes argumentrer (a\b,\B,\w, and\W It performs the following steps when called:
- LetbasicWordChars be the
CharSet containing every character inthe ASCII word characters . - LetextraWordChars be the
CharSet containing all charactersc such thatc is not inbasicWordChars butCanonicalize (rer,c) is inbasicWordChars. Assert :extraWordChars is empty unlessHasEitherUnicodeFlag (rer) istrue andrer.[[IgnoreCase]] istrue .- Return the union ofbasicWordChars andextraWordChars.
22.2.2.9.4 AllCharacters (rer )
The abstract operation AllCharacters takes argumentrer (a
- Ifrer.[[UnicodeSets]] is
true andrer.[[IgnoreCase]] istrue , then- Return the
CharSet containing all Unicode code pointsc that do not have aSimple Case Folding mapping (that is,scf (c)=c).
- Return the
- Else if
HasEitherUnicodeFlag (rer) istrue , then- Return the
CharSet containing all code point values.
- Return the
- Else,
- Return the
CharSet containing all code unit values.
- Return the
22.2.2.9.5 MaybeSimpleCaseFolding (rer,A )
The abstract operation MaybeSimpleCaseFolding takes argumentsrer (aCaseFolding.txt of the Unicode Character Database (each of which maps a single code point to another single code point) to map each
- Ifrer.[[UnicodeSets]] is
false orrer.[[IgnoreCase]] isfalse , returnA. - LetB be a new empty
CharSet . - For each
CharSetElement s ofA, do- Lett be an empty sequence of characters.
- For each single code pointcp ins, do
- Append
scf (cp) tot.
- Append
- Addt toB.
- ReturnB.
22.2.2.9.6 CharacterComplement (rer,S )
The abstract operation CharacterComplement takes argumentsrer (a
- LetA be
AllCharacters (rer). - Return the
CharSet containing the CharSetElements ofA which are not also CharSetElements ofS.
22.2.2.9.7 UnicodeMatchProperty (rer,p )
The abstract operation UnicodeMatchProperty takes argumentsrer (a
- Ifrer.[[UnicodeSets]] is
true andp is a Unicodeproperty name listed in the “Property name ” column ofTable 69 , then- Return the
List of Unicode code pointsp.
- Return the
Assert :p is a Unicodeproperty name or property alias listed in the “Property name and aliases” column ofTable 67 orTable 68 .- Letc be the canonical
property name ofp as given in the “Canonicalproperty name ” column of the corresponding row. - Return the
List of Unicode code pointsc.
Implementations must support the Unicode property names and aliases listed in
For example,Script_Extensions (scx (property alias) are valid, butscript_extensions orScx aren't.
The listed properties form a superset of whatUTS18 RL1.2 requires.
The spellings of entries in these tables (including casing) match the spellings used in the filePropertyAliases.txt in the Unicode Character Database. The precise spellings in that file areguaranteed to be stable.
| Canonical | |
|---|---|
General_Category | General_Category |
gc | |
Script | Script |
sc | |
Script_Extensions | Script_Extensions |
scx |
| Canonical | |
|---|---|
ASCII | ASCII |
ASCII_Hex_Digit | ASCII_Hex_Digit |
AHex | |
Alphabetic | Alphabetic |
Alpha | |
Any | Any |
Assigned | Assigned |
Bidi_Control | Bidi_Control |
Bidi_C | |
Bidi_Mirrored | Bidi_Mirrored |
Bidi_M | |
Case_Ignorable | Case_Ignorable |
CI | |
Cased | Cased |
Changes_When_Casefolded | Changes_When_Casefolded |
CWCF | |
Changes_When_Casemapped | Changes_When_Casemapped |
CWCM | |
Changes_When_Lowercased | Changes_When_Lowercased |
CWL | |
Changes_When_NFKC_Casefolded | Changes_When_NFKC_Casefolded |
CWKCF | |
Changes_When_Titlecased | Changes_When_Titlecased |
CWT | |
Changes_When_Uppercased | Changes_When_Uppercased |
CWU | |
Dash | Dash |
Default_Ignorable_Code_Point | Default_Ignorable_Code_Point |
DI | |
Deprecated | Deprecated |
Dep | |
Diacritic | Diacritic |
Dia | |
Emoji | Emoji |
Emoji_Component | Emoji_Component |
EComp | |
Emoji_Modifier | Emoji_Modifier |
EMod | |
Emoji_Modifier_Base | Emoji_Modifier_Base |
EBase | |
Emoji_Presentation | Emoji_Presentation |
EPres | |
Extended_Pictographic | Extended_Pictographic |
ExtPict | |
Extender | Extender |
Ext | |
Grapheme_Base | Grapheme_Base |
Gr_Base | |
Grapheme_Extend | Grapheme_Extend |
Gr_Ext | |
Hex_Digit | Hex_Digit |
Hex | |
IDS_Binary_Operator | IDS_Binary_Operator |
IDSB | |
IDS_Trinary_Operator | IDS_Trinary_Operator |
IDST | |
ID_Continue | ID_Continue |
IDC | |
ID_Start | ID_Start |
IDS | |
Ideographic | Ideographic |
Ideo | |
Join_Control | Join_Control |
Join_C | |
Logical_Order_Exception | Logical_Order_Exception |
LOE | |
Lowercase | Lowercase |
Lower | |
Math | Math |
Noncharacter_Code_Point | Noncharacter_Code_Point |
NChar | |
Pattern_Syntax | Pattern_Syntax |
Pat_Syn | |
Pattern_White_Space | Pattern_White_Space |
Pat_WS | |
Quotation_Mark | Quotation_Mark |
QMark | |
Radical | Radical |
Regional_Indicator | Regional_Indicator |
RI | |
Sentence_Terminal | Sentence_Terminal |
STerm | |
Soft_Dotted | Soft_Dotted |
SD | |
Terminal_Punctuation | Terminal_Punctuation |
Term | |
Unified_Ideograph | Unified_Ideograph |
UIdeo | |
Uppercase | Uppercase |
Upper | |
Variation_Selector | Variation_Selector |
VS | |
White_Space | White_Space |
space | |
XID_Continue | XID_Continue |
XIDC | |
XID_Start | XID_Start |
XIDS |
Basic_Emoji |
Emoji_Keycap_Sequence |
RGI_Emoji_Modifier_Sequence |
RGI_Emoji_Flag_Sequence |
RGI_Emoji_Tag_Sequence |
RGI_Emoji_ZWJ_Sequence |
RGI_Emoji |
22.2.2.9.8 UnicodeMatchPropertyValue (p,v )
The abstract operation UnicodeMatchPropertyValue takes argumentsp (
Assert :p is a canonical, unaliased Unicodeproperty name listed in the “Canonicalproperty name ” column ofTable 67 .Assert :v is a property value or property value alias for the Unicode propertyp listed inPropertyValueAliases.txt.- Letvalue be the canonical property value ofv as given in the “Canonical property value” column of the corresponding row.
- Return the
List of Unicode code pointsvalue.
Implementations must support the Unicode property values and property value aliases listed inPropertyValueAliases.txt for the properties listed in
For example,Xpeo andOld_Persian are validScript_Extensions values, butxpeo andOld Persian aren't.
This algorithm differs fromthe matching rules for symbolic values listed in UAX44: case,Is prefix is not supported.
22.2.2.10 Runtime Semantics: CompileClassSetString
The
- Return an empty sequence of characters.
- Return
CompileClassSetString ofNonEmptyClassString with argumentrer.
- Letcs be
CompileToCharSet ofClassSetCharacter with argumentrer. - Lets1 be the sequence of characters that is the single
CharSetElement ofcs. - If
NonEmptyClassString is present, then- Lets2 be
CompileClassSetString ofNonEmptyClassString with argumentrer. - Return the concatenation ofs1 ands2.
- Lets2 be
- Returns1.
22.2.3 Abstract Operations for RegExp Creation
22.2.3.1 RegExpCreate (P,F )
The abstract operation RegExpCreate takes argumentsP (an
- Letobj be !
RegExpAlloc (%RegExp% ). - Return ?
RegExpInitialize (obj,P,F).
22.2.3.2 RegExpAlloc (newTarget )
The abstract operation RegExpAlloc takes argumentnewTarget (a
- Letobj be ?
OrdinaryCreateFromConstructor (newTarget,"%RegExp.prototype%" , «[[OriginalSource]],[[OriginalFlags]],[[RegExpRecord]],[[RegExpMatcher]] »). - Perform !
DefinePropertyOrThrow (obj,"lastIndex" , PropertyDescriptor {[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }). - Returnobj.
22.2.3.3 RegExpInitialize (obj,pattern,flags )
The abstract operation RegExpInitialize takes argumentsobj (an Object),pattern (an
- Ifpattern is
undefined , letP be the empty String. - Else, letP be ?
ToString (pattern). - Ifflags is
undefined , letF be the empty String. - Else, letF be ?
ToString (flags). - IfF contains any code unit other than
"d" ,"g" ,"i" ,"m" ,"s" ,"u" ,"v" , or"y" , or ifF contains any code unit more than once, throw aSyntaxError exception. - IfF contains
"i" , leti betrue ; else leti befalse . - IfF contains
"m" , letm betrue ; else letm befalse . - IfF contains
"s" , lets betrue ; else lets befalse . - IfF contains
"u" , letu betrue ; else letu befalse . - IfF contains
"v" , letv betrue ; else letv befalse . - Ifu is
true orv istrue , then- LetpatternText be
StringToCodePoints (P).
- LetpatternText be
- Else,
- LetpatternText be the result of interpreting each ofP's 16-bit elements as a Unicode BMP code point. UTF-16 decoding is not applied to the elements.
- LetparseResult be
ParsePattern (patternText,u,v). - IfparseResult is a non-empty
List ofSyntaxError objects, throw aSyntaxError exception. Assert :parseResult is aPattern Parse Node .- Setobj.[[OriginalSource]] toP.
- Setobj.[[OriginalFlags]] toF.
- LetcapturingGroupsCount be
CountLeftCapturingParensWithin (parseResult). - Letrer be the
RegExp Record {[[IgnoreCase]]:i,[[Multiline]]:m,[[DotAll]]:s,[[Unicode]]:u,[[UnicodeSets]]:v,[[CapturingGroupsCount]]:capturingGroupsCount }. - Setobj.[[RegExpRecord]] torer.
- Setobj.[[RegExpMatcher]] to
CompilePattern ofparseResult with argumentrer. - Perform ?
Set (obj,"lastIndex" ,+0 𝔽,true ). - Returnobj.
22.2.3.4 Static Semantics: ParsePattern (patternText,u,v )
The abstract operation ParsePattern takes argumentspatternText (a sequence of Unicode code points),u (a Boolean), andv (a Boolean) and returns a
This section is amended in
It performs the following steps when called:
- Ifv is
true andu istrue , then- LetparseResult be a
List containing one or moreSyntaxError objects.
- LetparseResult be a
- Else ifv is
true , then - Else ifu is
true , then - Else,
- ReturnparseResult.
22.2.4 The RegExp Constructor
The RegExp
- is%RegExp%.
- is the initial value of the
"RegExp" property of theglobal object . - creates and initializes a new RegExp object when called as a
constructor . - when called as a function rather than as a
constructor , returns either a new RegExp object, or the argument itself if the only argument is a RegExp object. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified RegExp behaviour must include asupercall to the RegExpconstructor to create and initialize subclass instances with the necessary internal slots.
22.2.4.1 RegExp (pattern,flags )
This function performs the following steps when called:
- LetpatternIsRegExp be ?
IsRegExp (pattern). - If NewTarget is
undefined , then- LetnewTarget be the
active function object . - IfpatternIsRegExp is
true andflags isundefined , then
- LetnewTarget be the
- Else,
- LetnewTarget be NewTarget.
- Ifpattern
is an Object andpattern has a[[RegExpMatcher]] internal slot, then- LetP bepattern.[[OriginalSource]].
- Ifflags is
undefined , letF bepattern.[[OriginalFlags]]. - Else, letF beflags.
- Else ifpatternIsRegExp is
true , then - Else,
- LetP bepattern.
- LetF beflags.
- LetO be ?
RegExpAlloc (newTarget). - Return ?
RegExpInitialize (O,P,F).
If pattern is supplied using a
22.2.5 Properties of the RegExp Constructor
The RegExp
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
22.2.5.1 RegExp.prototype
The initial value ofRegExp.prototype is the
This property has the attributes {[[Writable]]:
22.2.5.2 get RegExp [ @@species ]
RegExp[@@species] is an
- Return the
this value.
The value of the
RegExp prototype methods normally use their
22.2.6 Properties of the RegExp Prototype Object
TheRegExp prototype object:
- is%RegExp.prototype%.
- is an
ordinary object . - is not a RegExp instance and does not have a[[RegExpMatcher]] internal slot or any of the other internal slots of RegExp instance objects.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% .
The RegExp prototype object does not have a
22.2.6.1 RegExp.prototype.constructor
The initial value ofRegExp.prototype.constructor is
22.2.6.2 RegExp.prototype.exec (string )
This method searchesstring for an occurrence of the regular expression pattern and returns an Array containing the results of the match, or
It performs the following steps when called:
- LetR be the
this value. - Perform ?
RequireInternalSlot (R,[[RegExpMatcher]]). - LetS be ?
ToString (string). - Return ?
RegExpBuiltinExec (R,S).
22.2.6.3 get RegExp.prototype.dotAll
RegExp.prototype.dotAll is an
- LetR be the
this value. - Letcu be the code unit 0x0073 (LATIN SMALL LETTER S).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.4 get RegExp.prototype.flags
RegExp.prototype.flags is an
- LetR be the
this value. - IfR
is not an Object , throw aTypeError exception. - LetcodeUnits be a new empty
List . - LethasIndices be
ToBoolean (?Get (R,"hasIndices" )). - IfhasIndices is
true , append the code unit 0x0064 (LATIN SMALL LETTER D) tocodeUnits. - Letglobal be
ToBoolean (?Get (R,"global" )). - Ifglobal is
true , append the code unit 0x0067 (LATIN SMALL LETTER G) tocodeUnits. - LetignoreCase be
ToBoolean (?Get (R,"ignoreCase" )). - IfignoreCase is
true , append the code unit 0x0069 (LATIN SMALL LETTER I) tocodeUnits. - Letmultiline be
ToBoolean (?Get (R,"multiline" )). - Ifmultiline is
true , append the code unit 0x006D (LATIN SMALL LETTER M) tocodeUnits. - LetdotAll be
ToBoolean (?Get (R,"dotAll" )). - IfdotAll is
true , append the code unit 0x0073 (LATIN SMALL LETTER S) tocodeUnits. - Letunicode be
ToBoolean (?Get (R,"unicode" )). - Ifunicode is
true , append the code unit 0x0075 (LATIN SMALL LETTER U) tocodeUnits. - LetunicodeSets be
ToBoolean (?Get (R,"unicodeSets" )). - IfunicodeSets is
true , append the code unit 0x0076 (LATIN SMALL LETTER V) tocodeUnits. - Letsticky be
ToBoolean (?Get (R,"sticky" )). - Ifsticky is
true , append the code unit 0x0079 (LATIN SMALL LETTER Y) tocodeUnits. - Return the String value whose code units are the elements of the
List codeUnits. IfcodeUnits has no elements, the empty String is returned.
22.2.6.4.1 RegExpHasFlag (R,codeUnit )
The abstract operation RegExpHasFlag takes argumentsR (an
- IfR
is not an Object , throw aTypeError exception. - IfR does not have an[[OriginalFlags]] internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , returnundefined . - Otherwise, throw a
TypeError exception.
- If
- Letflags beR.[[OriginalFlags]].
- Ifflags containscodeUnit, return
true . - Return
false .
22.2.6.5 get RegExp.prototype.global
RegExp.prototype.global is an
- LetR be the
this value. - Letcu be the code unit 0x0067 (LATIN SMALL LETTER G).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.6 get RegExp.prototype.hasIndices
RegExp.prototype.hasIndices is an
- LetR be the
this value. - Letcu be the code unit 0x0064 (LATIN SMALL LETTER D).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.7 get RegExp.prototype.ignoreCase
RegExp.prototype.ignoreCase is an
- LetR be the
this value. - Letcu be the code unit 0x0069 (LATIN SMALL LETTER I).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.8 RegExp.prototype [ @@match ] (string )
This method performs the following steps when called:
- Letrx be the
this value. - Ifrx
is not an Object , throw aTypeError exception. - LetS be ?
ToString (string). - Letflags be ?
ToString (?Get (rx,"flags" )). - Ifflags does not contain
"g" , then- Return ?
RegExpExec (rx,S).
- Return ?
- Else,
- Ifflags contains
"u" orflags contains"v" , letfullUnicode betrue . Otherwise, letfullUnicode befalse . - Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ). - LetA be !
ArrayCreate (0). - Letn be 0.
- Repeat,
- Letresult be ?
RegExpExec (rx,S). - Ifresult is
null , then- Ifn = 0, return
null . - ReturnA.
- Ifn = 0, return
- Else,
- LetmatchStr be ?
ToString (?Get (result,"0" )). - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),matchStr). - IfmatchStr is the empty String, then
- Setn ton + 1.
- LetmatchStr be ?
- Letresult be ?
- Ifflags contains
The value of the
The
22.2.6.9 RegExp.prototype [ @@matchAll ] (string )
This method performs the following steps when called:
- LetR be the
this value. - IfR
is not an Object , throw aTypeError exception. - LetS be ?
ToString (string). - LetC be ?
SpeciesConstructor (R,%RegExp% ). - Letflags be ?
ToString (?Get (R,"flags" )). - Letmatcher be ?
Construct (C, «R,flags »). - LetlastIndex be ?
ToLength (?Get (R,"lastIndex" )). - Perform ?
Set (matcher,"lastIndex" ,lastIndex,true ). - Ifflags contains
"g" , letglobal betrue . - Else, letglobal be
false . - Ifflags contains
"u" orflags contains"v" , letfullUnicode betrue . - Else, letfullUnicode be
false . - Return
CreateRegExpStringIterator (matcher,S,global,fullUnicode).
The value of the
22.2.6.10 get RegExp.prototype.multiline
RegExp.prototype.multiline is an
- LetR be the
this value. - Letcu be the code unit 0x006D (LATIN SMALL LETTER M).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.11 RegExp.prototype [ @@replace ] (string,replaceValue )
This method performs the following steps when called:
- Letrx be the
this value. - Ifrx
is not an Object , throw aTypeError exception. - LetS be ?
ToString (string). - LetlengthS be the length ofS.
- LetfunctionalReplace be
IsCallable (replaceValue). - IffunctionalReplace is
false , then- SetreplaceValue to ?
ToString (replaceValue).
- SetreplaceValue to ?
- Letflags be ?
ToString (?Get (rx,"flags" )). - Ifflags contains
"g" , letglobal betrue . Otherwise, letglobal befalse . - Ifglobal is
true , then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Letresults be a new empty
List . - Letdone be
false . - Repeat, whiledone is
false ,- Letresult be ?
RegExpExec (rx,S). - Ifresult is
null , then- Setdone to
true .
- Setdone to
- Else,
- Letresult be ?
- LetaccumulatedResult be the empty String.
- LetnextSourcePosition be 0.
- For each elementresult ofresults, do
- LetresultLength be ?
LengthOfArrayLike (result). - LetnCaptures be
max (resultLength - 1, 0). - Letmatched be ?
ToString (?Get (result,"0" )). - LetmatchLength be the length ofmatched.
- Letposition be ?
ToIntegerOrInfinity (?Get (result,"index" )). - Setposition to the result of
clamping position between 0 andlengthS. - Letcaptures be a new empty
List . - Letn be 1.
- Repeat, whilen ≤nCaptures,
- LetcapN be ?
Get (result, !ToString (𝔽 (n))). - IfcapN is not
undefined , then- SetcapN to ?
ToString (capN).
- SetcapN to ?
- AppendcapN tocaptures.
- NOTE: Whenn = 1, the preceding step puts the first element intocaptures (at index 0). More generally, thenth capture (the characters captured by thenth set of capturing parentheses) is atcaptures[n - 1].
- Setn ton + 1.
- LetcapN be ?
- LetnamedCaptures be ?
Get (result,"groups" ). - IffunctionalReplace is
true , then- LetreplacerArgs be the
list-concatenation of «matched »,captures, and «𝔽 (position),S ». - IfnamedCaptures is not
undefined , then- AppendnamedCaptures toreplacerArgs.
- LetreplValue be ?
Call (replaceValue,undefined ,replacerArgs). - Letreplacement be ?
ToString (replValue).
- LetreplacerArgs be the
- Else,
- IfnamedCaptures is not
undefined , then- SetnamedCaptures to ?
ToObject (namedCaptures).
- SetnamedCaptures to ?
- Letreplacement be ?
GetSubstitution (matched,S,position,captures,namedCaptures,replaceValue).
- IfnamedCaptures is not
- Ifposition ≥nextSourcePosition, then
- NOTE:position should not normally move backwards. If it does, it is an indication of an ill-behaving RegExp subclass or use of an access triggered side-effect to change the global flag or other characteristics ofrx. In such cases, the corresponding substitution is ignored.
- SetaccumulatedResult to the
string-concatenation ofaccumulatedResult, thesubstring ofS fromnextSourcePosition toposition, andreplacement. - SetnextSourcePosition toposition +matchLength.
- LetresultLength be ?
- IfnextSourcePosition ≥lengthS, returnaccumulatedResult.
- Return the
string-concatenation ofaccumulatedResult and thesubstring ofS fromnextSourcePosition.
The value of the
22.2.6.12 RegExp.prototype [ @@search ] (string )
This method performs the following steps when called:
- Letrx be the
this value. - Ifrx
is not an Object , throw aTypeError exception. - LetS be ?
ToString (string). - LetpreviousLastIndex be ?
Get (rx,"lastIndex" ). - If
SameValue (previousLastIndex,+0 𝔽) isfalse , then- Perform ?
Set (rx,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Letresult be ?
RegExpExec (rx,S). - LetcurrentLastIndex be ?
Get (rx,"lastIndex" ). - If
SameValue (currentLastIndex,previousLastIndex) isfalse , then- Perform ?
Set (rx,"lastIndex" ,previousLastIndex,true ).
- Perform ?
- Ifresult is
null , return-1 𝔽. - Return ?
Get (result,"index" ).
The value of the
The
22.2.6.13 get RegExp.prototype.source
RegExp.prototype.source is an
- LetR be the
this value. - IfR
is not an Object , throw aTypeError exception. - IfR does not have an[[OriginalSource]] internal slot, then
- If
SameValue (R,%RegExp.prototype% ) istrue , return"(?:)" . - Otherwise, throw a
TypeError exception.
- If
Assert :R has an[[OriginalFlags]] internal slot.- Letsrc beR.[[OriginalSource]].
- Letflags beR.[[OriginalFlags]].
- Return
EscapeRegExpPattern (src,flags).
22.2.6.13.1 EscapeRegExpPattern (P,F )
The abstract operation EscapeRegExpPattern takes argumentsP (a String) andF (a String) and returns a String. It performs the following steps when called:
- IfF contains
"v" , then- LetpatternSymbol be
Pattern .[+UnicodeMode, +UnicodeSetsMode]
- LetpatternSymbol be
- Else ifF contains
"u" , then- LetpatternSymbol be
Pattern .[+UnicodeMode, ~UnicodeSetsMode]
- LetpatternSymbol be
- Else,
- LetpatternSymbol be
Pattern .[~UnicodeMode, ~UnicodeSetsMode]
- LetpatternSymbol be
- LetS be a String in the form of apatternSymbol equivalent toP interpreted as UTF-16 encoded Unicode code points (
6.1.4 ), in which certain code points are escaped as described below.S may or may not differ fromP; however, theAbstract Closure that would result from evaluatingS as apatternSymbol must behave identically to theAbstract Closure given by the constructed object's[[RegExpMatcher]] internal slot. Multiple calls to this abstract operation using the same values forP andF must produce identical results. - The code points
/or anyLineTerminator occurring in the pattern shall be escaped inS as necessary to ensure that thestring-concatenation of"/" ,S,"/" , andF can be parsed (in an appropriate lexical context) as aRegularExpressionLiteral that behaves identically to the constructed regular expression. For example, ifP is"/" , thenS could be"\/" or"\u002F" , among other possibilities, but not"/" , because///followed byF would be parsed as aSingleLineComment rather than aRegularExpressionLiteral . IfP is the empty String, this specification can be met by lettingS be"(?:)" . - ReturnS.
22.2.6.14 RegExp.prototype [ @@split ] (string,limit )
This method returns an Array into which substrings of the result of convertingstring to a String have been stored. The substrings are determined by searching from left to right for matches of the
The/a*?/[Symbol.split]("ab") evaluates to the array["a", "b"], while/a*/[Symbol.split]("ab") evaluates to the array["","b"].)
Ifstring is (or converts to) the empty String, the result depends on whether the regular expression can match the empty String. If it can, the result array contains no elements. Otherwise, the result array contains one element, which is the empty String.
If the regular expression contains capturing parentheses, then each timeseparator is matched the results (including any
/<(\/)?([^<>]+)>/[Symbol.split]("A<B>bold</B>and<CODE>coded</CODE>")evaluates to the array
["A",undefined,"B","bold","/","B","and",undefined,"CODE","coded","/","CODE",""]Iflimit is not
This method performs the following steps when called:
- Letrx be the
this value. - Ifrx
is not an Object , throw aTypeError exception. - LetS be ?
ToString (string). - LetC be ?
SpeciesConstructor (rx,%RegExp% ). - Letflags be ?
ToString (?Get (rx,"flags" )). - Ifflags contains
"u" orflags contains"v" , letunicodeMatching betrue . - Else, letunicodeMatching be
false . - Ifflags contains
"y" , letnewFlags beflags. - Else, letnewFlags be the
string-concatenation offlags and"y" . - Letsplitter be ?
Construct (C, «rx,newFlags »). - LetA be !
ArrayCreate (0). - LetlengthA be 0.
- Iflimit is
undefined , letlim be 232 - 1; else letlim beℝ (?ToUint32 (limit)). - Iflim = 0, returnA.
- IfS is the empty String, then
- Letz be ?
RegExpExec (splitter,S). - Ifz is not
null , returnA. - Perform !
CreateDataPropertyOrThrow (A,"0" ,S). - ReturnA.
- Letz be ?
- Letsize be the length ofS.
- Letp be 0.
- Letq bep.
- Repeat, whileq <size,
- Perform ?
Set (splitter,"lastIndex" ,𝔽 (q),true ). - Letz be ?
RegExpExec (splitter,S). - Ifz is
null , then- Setq to
AdvanceStringIndex (S,q,unicodeMatching).
- Setq to
- Else,
- Lete be
ℝ (?ToLength (?Get (splitter,"lastIndex" ))). - Sete to
min (e,size). - Ife =p, then
- Setq to
AdvanceStringIndex (S,q,unicodeMatching).
- Setq to
- Else,
- LetT be the
substring ofS fromp toq. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)),T). - SetlengthA tolengthA + 1.
- IflengthA =lim, returnA.
- Setp toe.
- LetnumberOfCaptures be ?
LengthOfArrayLike (z). - SetnumberOfCaptures to
max (numberOfCaptures - 1, 0). - Leti be 1.
- Repeat, whilei ≤numberOfCaptures,
- Setq top.
- LetT be the
- Lete be
- Perform ?
- LetT be the
substring ofS fromp tosize. - Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (lengthA)),T). - ReturnA.
The value of the
This method ignores the value of the
22.2.6.15 get RegExp.prototype.sticky
RegExp.prototype.sticky is an
- LetR be the
this value. - Letcu be the code unit 0x0079 (LATIN SMALL LETTER Y).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.16 RegExp.prototype.test (S )
This method performs the following steps when called:
- LetR be the
this value. - IfR
is not an Object , throw aTypeError exception. - Letstring be ?
ToString (S). - Letmatch be ?
RegExpExec (R,string). - Ifmatch is not
null , returntrue ; else returnfalse .
22.2.6.17 RegExp.prototype.toString ( )
- LetR be the
this value. - IfR
is not an Object , throw aTypeError exception. - Letpattern be ?
ToString (?Get (R,"source" )). - Letflags be ?
ToString (?Get (R,"flags" )). - Letresult be the
string-concatenation of"/" ,pattern,"/" , andflags. - Returnresult.
The returned String has the form of a
22.2.6.18 get RegExp.prototype.unicode
RegExp.prototype.unicode is an
- LetR be the
this value. - Letcu be the code unit 0x0075 (LATIN SMALL LETTER U).
- Return ?
RegExpHasFlag (R,cu).
22.2.6.19 get RegExp.prototype.unicodeSets
RegExp.prototype.unicodeSets is an
- LetR be the
this value. - Letcu be the code unit 0x0076 (LATIN SMALL LETTER V).
- Return ?
RegExpHasFlag (R,cu).
22.2.7 Abstract Operations for RegExp Matching
22.2.7.1 RegExpExec (R,S )
The abstract operation RegExpExec takes argumentsR (an Object) andS (a String) and returns either a
- Letexec be ?
Get (R,"exec" ). - If
IsCallable (exec) istrue , then- Letresult be ?
Call (exec,R, «S »). - Ifresult
is not an Object andresult is notnull , throw aTypeError exception. - Returnresult.
- Letresult be ?
- Perform ?
RequireInternalSlot (R,[[RegExpMatcher]]). - Return ?
RegExpBuiltinExec (R,S).
If a callable
22.2.7.2 RegExpBuiltinExec (R,S )
The abstract operation RegExpBuiltinExec takes argumentsR (an initialized RegExp instance) andS (a String) and returns either a
- Letlength be the length ofS.
- LetlastIndex be
ℝ (?ToLength (?Get (R,"lastIndex" ))). - Letflags beR.[[OriginalFlags]].
- Ifflags contains
"g" , letglobal betrue ; else letglobal befalse . - Ifflags contains
"y" , letsticky betrue ; else letsticky befalse . - Ifflags contains
"d" , lethasIndices betrue ; else lethasIndices befalse . - Ifglobal is
false andsticky isfalse , setlastIndex to 0. - Letmatcher beR.[[RegExpMatcher]].
- Ifflags contains
"u" orflags contains"v" , letfullUnicode betrue ; else letfullUnicode befalse . - LetmatchSucceeded be
false . - IffullUnicode is
true , letinput beStringToCodePoints (S). Otherwise, letinput be aList whose elements are the code units that are the elements ofS. - NOTE: Each element ofinput is considered to be a character.
- Repeat, whilematchSucceeded is
false ,- IflastIndex >length, then
- Ifglobal is
true orsticky istrue , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ).
- Perform ?
- Return
null .
- Ifglobal is
- LetinputIndex be the index intoinput of the character that was obtained from elementlastIndex ofS.
- Letr bematcher(input,inputIndex).
- Ifr is
failure , then- Ifsticky is
true , then- Perform ?
Set (R,"lastIndex" ,+0 𝔽,true ). - Return
null .
- Perform ?
- SetlastIndex to
AdvanceStringIndex (S,lastIndex,fullUnicode).
- Ifsticky is
- Else,
Assert :r is aMatchState .- SetmatchSucceeded to
true .
- IflastIndex >length, then
- Lete ber.[[EndIndex]].
- IffullUnicode is
true , sete toGetStringIndex (S,e). - Ifglobal is
true orsticky istrue , then - Letn be the number of elements inr.[[Captures]].
Assert :n =R.[[RegExpRecord]].[[CapturingGroupsCount]].Assert :n < 232 - 1.- LetA be !
ArrayCreate (n + 1). Assert : Themathematical value of A's"length" property isn + 1.- Perform !
CreateDataPropertyOrThrow (A,"index" ,𝔽 (lastIndex)). - Perform !
CreateDataPropertyOrThrow (A,"input" ,S). - Letmatch be the
Match Record {[[StartIndex]]:lastIndex,[[EndIndex]]:e }. - Letindices be a new empty
List . - LetgroupNames be a new empty
List . - Appendmatch toindices.
- LetmatchedSubstr be
GetMatchString (S,match). - Perform !
CreateDataPropertyOrThrow (A,"0" ,matchedSubstr). - IfR contains any
GroupName , then- Letgroups be
OrdinaryObjectCreate (null ). - LethasGroups be
true .
- Letgroups be
- Else,
- Letgroups be
undefined . - LethasGroups be
false .
- Letgroups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" ,groups). - For each
integer i such that 1 ≤i ≤n, in ascending order, do- LetcaptureI beith element ofr.[[Captures]].
- IfcaptureI is
undefined , then- LetcapturedValue be
undefined . - Append
undefined toindices.
- LetcapturedValue be
- Else,
- LetcaptureStart becaptureI.[[StartIndex]].
- LetcaptureEnd becaptureI.[[EndIndex]].
- IffullUnicode is
true , then- SetcaptureStart to
GetStringIndex (S,captureStart). - SetcaptureEnd to
GetStringIndex (S,captureEnd).
- SetcaptureStart to
- Letcapture be the
Match Record {[[StartIndex]]:captureStart,[[EndIndex]]:captureEnd }. - LetcapturedValue be
GetMatchString (S,capture). - Appendcapture toindices.
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)),capturedValue). - If theith capture ofR was defined with a
GroupName , then- Lets be the
CapturingGroupName of thatGroupName . - Perform !
CreateDataPropertyOrThrow (groups,s,capturedValue). - Appends togroupNames.
- Lets be the
- Else,
- Append
undefined togroupNames.
- Append
- IfhasIndices is
true , then- LetindicesArray be
MakeMatchIndicesIndexPairArray (S,indices,groupNames,hasGroups). - Perform !
CreateDataPropertyOrThrow (A,"indices" ,indicesArray).
- LetindicesArray be
- ReturnA.
22.2.7.3 AdvanceStringIndex (S,index,unicode )
The abstract operation AdvanceStringIndex takes argumentsS (a String),index (a non-negative
Assert :index ≤ 253 - 1.- Ifunicode is
false , returnindex + 1. - Letlength be the length ofS.
- Ifindex + 1 ≥length, returnindex + 1.
- Letcp be
CodePointAt (S,index). - Returnindex +cp.[[CodeUnitCount]].
22.2.7.4 GetStringIndex (S,codePointIndex )
The abstract operation GetStringIndex takes argumentsS (a String) andcodePointIndex (a non-negative
- IfS is the empty String, return 0.
- Letlen be the length ofS.
- LetcodeUnitCount be 0.
- LetcodePointCount be 0.
- Repeat, whilecodeUnitCount <len,
- IfcodePointCount =codePointIndex, returncodeUnitCount.
- Letcp be
CodePointAt (S,codeUnitCount). - SetcodeUnitCount tocodeUnitCount +cp.[[CodeUnitCount]].
- SetcodePointCount tocodePointCount + 1.
- Returnlen.
22.2.7.5 Match Records
AMatch Record is a
Match Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[StartIndex]] | a non-negative | The number of code units from the start of a string at which the match begins (inclusive). |
| [[EndIndex]] | an | The number of code units from the start of a string at which the match ends (exclusive). |
22.2.7.6 GetMatchString (S,match )
The abstract operation GetMatchString takes argumentsS (a String) andmatch (a
22.2.7.7 GetMatchIndexPair (S,match )
The abstract operation GetMatchIndexPair takes argumentsS (a String) andmatch (a
Assert :match.[[StartIndex]] ≤match.[[EndIndex]] ≤ the length ofS.- Return
CreateArrayFromList («𝔽 (match.[[StartIndex]]),𝔽 (match.[[EndIndex]]) »).
22.2.7.8 MakeMatchIndicesIndexPairArray (S,indices,groupNames,hasGroups )
The abstract operation MakeMatchIndicesIndexPairArray takes argumentsS (a String),indices (a
- Letn be the number of elements inindices.
Assert :n < 232 - 1.Assert :groupNames hasn - 1 elements.- NOTE: ThegroupNames
List contains elements aligned with theindicesList starting atindices[1]. - LetA be !
ArrayCreate (n). - IfhasGroups is
true , then- Letgroups be
OrdinaryObjectCreate (null ).
- Letgroups be
- Else,
- Letgroups be
undefined .
- Letgroups be
- Perform !
CreateDataPropertyOrThrow (A,"groups" ,groups). - For each
integer i such that 0 ≤i <n, in ascending order, do- LetmatchIndices beindices[i].
- IfmatchIndices is not
undefined , then- LetmatchIndexPair be
GetMatchIndexPair (S,matchIndices).
- LetmatchIndexPair be
- Else,
- LetmatchIndexPair be
undefined .
- LetmatchIndexPair be
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (i)),matchIndexPair). - Ifi > 0 andgroupNames[i - 1] is not
undefined , thenAssert :groups is notundefined .- Perform !
CreateDataPropertyOrThrow (groups,groupNames[i - 1],matchIndexPair).
- ReturnA.
22.2.8 Properties of RegExp Instances
RegExp instances are
Prior to ECMAScript 2015, RegExp instances were specified as having the ownRegExp.prototype.
RegExp instances also have the following property:
22.2.8.1 lastIndex
The value of the
22.2.9 RegExp String Iterator Objects
A RegExp String Iterator is an object, that represents a specific iteration over some specific String instance object, matching against some specific RegExp instance object. There is not a named
22.2.9.1 CreateRegExpStringIterator (R,S,global,fullUnicode )
The abstract operation CreateRegExpStringIterator takes argumentsR (an Object),S (a String),global (a Boolean), andfullUnicode (a Boolean) and returns a Generator. It performs the following steps when called:
- Letclosure be a new
Abstract Closure with no parameters that capturesR,S,global, andfullUnicode and performs the following steps when called:- Repeat,
- Letmatch be ?
RegExpExec (R,S). - Ifmatch is
null , returnundefined . - Ifglobal is
false , then- Perform ?
GeneratorYield (CreateIterResultObject (match,false )). - Return
undefined .
- Perform ?
- LetmatchStr be ?
ToString (?Get (match,"0" )). - IfmatchStr is the empty String, then
- Perform ?
GeneratorYield (CreateIterResultObject (match,false )).
- Letmatch be ?
- Repeat,
- Return
CreateIteratorFromClosure (closure,"%RegExpStringIteratorPrototype%" ,%RegExpStringIteratorPrototype% ).
22.2.9.2 The %RegExpStringIteratorPrototype% Object
The%RegExpStringIteratorPrototype% object:
- has properties that are inherited by all RegExp String Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
22.2.9.2.1 %RegExpStringIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%RegExpStringIteratorPrototype%" ).
22.2.9.2.2 %RegExpStringIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
23 Indexed Collections
23.1 Array Objects
Arrays are
23.1.1 The Array Constructor
The Array
- is%Array%.
- is the initial value of the
"Array" property of theglobal object . - creates and initializes a new Array when called as a
constructor . - also creates and initializes a new Array when called as a function rather than as a
constructor . Thus the function callArray(…)is equivalent to the object creation expressionnew Array(…)with the same arguments. - is a function whose behaviour differs based upon the number and types of its arguments.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the exotic Array behaviour must include asupercall to the Arrayconstructor to initialize subclass instances that areArray exotic objects . However, most of theArray.prototypemethods are generic methods that are not dependent upon theirthis value being anArray exotic object .
23.1.1.1 Array ( ...values )
This function performs the following steps when called:
- If NewTarget is
undefined , letnewTarget be theactive function object ; else letnewTarget be NewTarget. - Letproto be ?
GetPrototypeFromConstructor (newTarget,"%Array.prototype%" ). - LetnumberOfArgs be the number of elements invalues.
- IfnumberOfArgs = 0, then
- Return !
ArrayCreate (0,proto).
- Return !
- Else ifnumberOfArgs = 1, then
- Letlen bevalues[0].
- Letarray be !
ArrayCreate (0,proto). - Iflen
is not a Number , then- Perform !
CreateDataPropertyOrThrow (array,"0" ,len). - LetintLen be
1 𝔽.
- Perform !
- Else,
- LetintLen be !
ToUint32 (len). - If
SameValueZero (intLen,len) isfalse , throw aRangeError exception.
- LetintLen be !
- Perform !
Set (array,"length" ,intLen,true ). - Returnarray.
- Else,
Assert :numberOfArgs ≥ 2.- Letarray be ?
ArrayCreate (numberOfArgs,proto). - Letk be 0.
- Repeat, whilek <numberOfArgs,
- LetPk be !
ToString (𝔽 (k)). - LetitemK bevalues[k].
- Perform !
CreateDataPropertyOrThrow (array,Pk,itemK). - Setk tok + 1.
- LetPk be !
Assert : Themathematical value of array's"length" property isnumberOfArgs.- Returnarray.
23.1.2 Properties of the Array Constructor
The Array
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"length" property whose value is1 𝔽. - has the following properties:
23.1.2.1 Array.from (items [ ,mapfn [ ,thisArg ] ] )
This method performs the following steps when called:
- LetC be the
this value. - Ifmapfn is
undefined , then- Letmapping be
false .
- Letmapping be
- Else,
- If
IsCallable (mapfn) isfalse , throw aTypeError exception. - Letmapping be
true .
- If
- LetusingIterator be ?
GetMethod (items,@@iterator ). - IfusingIterator is not
undefined , then- If
IsConstructor (C) istrue , then- LetA be ?
Construct (C).
- LetA be ?
- Else,
- LetA be !
ArrayCreate (0).
- LetA be !
- LetiteratorRecord be ?
GetIteratorFromMethod (items,usingIterator). - Letk be 0.
- Repeat,
- Ifk ≥ 253 - 1, then
- Leterror be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord,error).
- Leterror be
- LetPk be !
ToString (𝔽 (k)). - Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then - Ifmapping is
true , then- LetmappedValue be
Completion (Call (mapfn,thisArg, «next,𝔽 (k) »)). IfAbruptCloseIterator (mappedValue,iteratorRecord).
- LetmappedValue be
- Else,
- LetmappedValue benext.
- LetdefineStatus be
Completion (CreateDataPropertyOrThrow (A,Pk,mappedValue)). IfAbruptCloseIterator (defineStatus,iteratorRecord).- Setk tok + 1.
- Ifk ≥ 253 - 1, then
- If
- NOTE:items is not an Iterable so assume it is an
array-like object . - LetarrayLike be !
ToObject (items). - Letlen be ?
LengthOfArrayLike (arrayLike). - If
IsConstructor (C) istrue , then - Else,
- LetA be ?
ArrayCreate (len).
- LetA be ?
- Letk be 0.
- Repeat, whilek <len,
- Perform ?
Set (A,"length" ,𝔽 (len),true ). - ReturnA.
This method is an intentionally generic factory method; it does not require that its
23.1.2.2 Array.isArray (arg )
This function performs the following steps when called:
- Return ?
IsArray (arg).
23.1.2.3 Array.of ( ...items )
This method performs the following steps when called:
- Letlen be the number of elements initems.
- LetlenNumber be
𝔽 (len). - LetC be the
this value. - If
IsConstructor (C) istrue , then- LetA be ?
Construct (C, «lenNumber »).
- LetA be ?
- Else,
- LetA be ?
ArrayCreate (len).
- LetA be ?
- Letk be 0.
- Repeat, whilek <len,
- LetkValue beitems[k].
- LetPk be !
ToString (𝔽 (k)). - Perform ?
CreateDataPropertyOrThrow (A,Pk,kValue). - Setk tok + 1.
- Perform ?
Set (A,"length" ,lenNumber,true ). - ReturnA.
This method is an intentionally generic factory method; it does not require that its
23.1.2.4 Array.prototype
The value ofArray.prototype is the
This property has the attributes {[[Writable]]:
23.1.2.5 get Array [ @@species ]
Array[@@species] is an
- Return the
this value.
The value of the
Array prototype methods normally use their
23.1.3 Properties of the Array Prototype Object
TheArray prototype object:
- is%Array.prototype%.
- is an
Array exotic object and has the internal methods specified for such objects. - has a
"length" property whose initial value is+0 𝔽 and whose attributes are {[[Writable]]:true ,[[Enumerable]]:false ,[[Configurable]]:false }. - has a[[Prototype]] internal slot whose value is
%Object.prototype% .
The Array prototype object is specified to be an
23.1.3.1 Array.prototype.at (index )
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeIndex be ?
ToIntegerOrInfinity (index). - IfrelativeIndex ≥ 0, then
- Letk berelativeIndex.
- Else,
- Letk belen +relativeIndex.
- Ifk < 0 ork ≥len, return
undefined . - Return ?
Get (O, !ToString (𝔽 (k))).
23.1.3.2 Array.prototype.concat ( ...items )
This method returns an array containing the array elements of the object followed by the array elements of each argument.
It performs the following steps when called:
- LetO be ?
ToObject (this value). - LetA be ?
ArraySpeciesCreate (O, 0). - Letn be 0.
- PrependO toitems.
- For each elementE ofitems, do
- Letspreadable be ?
IsConcatSpreadable (E). - Ifspreadable is
true , then- Letlen be ?
LengthOfArrayLike (E). - Ifn +len > 253 - 1, throw a
TypeError exception. - Letk be 0.
- Repeat, whilek <len,
- LetPk be !
ToString (𝔽 (k)). - Letexists be ?
HasProperty (E,Pk). - Ifexists is
true , then- LetsubElement be ?
Get (E,Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),subElement).
- LetsubElement be ?
- Setn ton + 1.
- Setk tok + 1.
- LetPk be !
- Letlen be ?
- Else,
- NOTE:E is added as a single item rather than spread.
- Ifn ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),E). - Setn ton + 1.
- Letspreadable be ?
- Perform ?
Set (A,"length" ,𝔽 (n),true ). - ReturnA.
The
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.2.1 IsConcatSpreadable (O )
The abstract operation IsConcatSpreadable takes argumentO (an
- IfO
is not an Object , returnfalse . - Letspreadable be ?
Get (O,@@isConcatSpreadable ). - Ifspreadable is not
undefined , returnToBoolean (spreadable). - Return ?
IsArray (O).
23.1.3.3 Array.prototype.constructor
The initial value ofArray.prototype.constructor is
23.1.3.4 Array.prototype.copyWithin (target,start [ ,end ] )
Theend argument is optional. If it is not provided, the length of the
Iftarget is negative, it is treated as
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeTarget be ?
ToIntegerOrInfinity (target). - IfrelativeTarget = -∞, letto be 0.
- Else ifrelativeTarget < 0, letto be
max (len +relativeTarget, 0). - Else, letto be
min (relativeTarget,len). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letfrom be 0.
- Else ifrelativeStart < 0, letfrom be
max (len +relativeStart, 0). - Else, letfrom be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letfinal be 0.
- Else ifrelativeEnd < 0, letfinal be
max (len +relativeEnd, 0). - Else, letfinal be
min (relativeEnd,len). - Letcount be
min (final -from,len -to). - Iffrom <to andto <from +count, then
- Letdirection be -1.
- Setfrom tofrom +count - 1.
- Setto toto +count - 1.
- Else,
- Letdirection be 1.
- Repeat, whilecount > 0,
- LetfromKey be !
ToString (𝔽 (from)). - LettoKey be !
ToString (𝔽 (to)). - LetfromPresent be ?
HasProperty (O,fromKey). - IffromPresent is
true , then - Else,
Assert :fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O,toKey).
- Setfrom tofrom +direction.
- Setto toto +direction.
- Setcount tocount - 1.
- LetfromKey be !
- ReturnO.
This method is intentionally generic; it does not require that its
23.1.3.5 Array.prototype.entries ( )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Return
CreateArrayIterator (O,key+value ).
23.1.3.6 Array.prototype.every (callbackfn [ ,thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that is coercible to a Boolean value.every callscallbackfn once for each element present in the array, in ascending order, until it finds one wherecallbackfn returnsevery immediately returnsevery will return
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
every does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed byevery is set before the first call tocallbackfn. Elements which are appended to the array after the call toevery begins will not be visited bycallbackfn. If existing elements of the array are changed, their value as passed tocallbackfn will be the value at the timeevery visits them; elements that are deleted after the call toevery begins and before being visited are not visited.every acts like the "for all" quantifier in mathematics. In particular, for an empty array, it returns
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
true .
This method is intentionally generic; it does not require that its
23.1.3.7 Array.prototype.fill (value [ ,start [ ,end ] ] )
Thestart argument is optional. If it is not provided,
Theend argument is optional. If it is not provided, the length of the
Ifstart is negative, it is treated as
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letk be 0.
- Else ifrelativeStart < 0, letk be
max (len +relativeStart, 0). - Else, letk be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letfinal be 0.
- Else ifrelativeEnd < 0, letfinal be
max (len +relativeEnd, 0). - Else, letfinal be
min (relativeEnd,len). - Repeat, whilek <final,
- ReturnO.
This method is intentionally generic; it does not require that its
23.1.3.8 Array.prototype.filter (callbackfn [ ,thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that is coercible to a Boolean value.filter callscallbackfn once for each element in the array, in ascending order, and constructs a new array of all the values for whichcallbackfn returns
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
filter does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed byfilter is set before the first call tocallbackfn. Elements which are appended to the array after the call tofilter begins will not be visited bycallbackfn. If existing elements of the array are changed their value as passed tocallbackfn will be the value at the timefilter visits them; elements that are deleted after the call tofilter begins and before being visited are not visited.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - LetA be ?
ArraySpeciesCreate (O, 0). - Letk be 0.
- Letto be 0.
- Repeat, whilek <len,
- LetPk be !
ToString (𝔽 (k)). - LetkPresent be ?
HasProperty (O,Pk). - IfkPresent is
true , then - Setk tok + 1.
- LetPk be !
- ReturnA.
This method is intentionally generic; it does not require that its
23.1.3.9 Array.prototype.find (predicate [ ,thisArg ] )
This method callspredicate once for each element of the array, in ascending index order, until it finds one wherepredicate returns a value that coerces tofind immediately returns that element value. Otherwise,find returns
See
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetfindRec be ?
FindViaPredicate (O,len,ascending ,predicate,thisArg). - ReturnfindRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.10 Array.prototype.findIndex (predicate [ ,thisArg ] )
This method callspredicate once for each element of the array, in ascending index order, until it finds one wherepredicate returns a value that coerces tofindIndex immediately returns the index of that element value. Otherwise,findIndex returns -1.
See
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetfindRec be ?
FindViaPredicate (O,len,ascending ,predicate,thisArg). - ReturnfindRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.11 Array.prototype.findLast (predicate [ ,thisArg ] )
This method callspredicate once for each element of the array, in descending index order, until it finds one wherepredicate returns a value that coerces tofindLast immediately returns that element value. Otherwise,findLast returns
See
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetfindRec be ?
FindViaPredicate (O,len,descending ,predicate,thisArg). - ReturnfindRec.[[Value]].
This method is intentionally generic; it does not require that its
23.1.3.12 Array.prototype.findLastIndex (predicate [ ,thisArg ] )
This method callspredicate once for each element of the array, in descending index order, until it finds one wherepredicate returns a value that coerces tofindLastIndex immediately returns the index of that element value. Otherwise,findLastIndex returns -1.
See
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetfindRec be ?
FindViaPredicate (O,len,descending ,predicate,thisArg). - ReturnfindRec.[[Index]].
This method is intentionally generic; it does not require that its
23.1.3.12.1 FindViaPredicate (O,len,direction,predicate,thisArg )
The abstract operation FindViaPredicate takes argumentsO (an Object),len (a non-negative
O should be an
predicate should be a function. When called for an element of the array, it is passed three arguments: the value of the element, the index of the element, and the object being traversed. Its return value will be coerced to a Boolean value.
thisArg will be used as the
This operation does not directly mutate the object on which it is called, but the object may be mutated by the calls topredicate.
The range of elements processed is set before the first call topredicate, just before the traversal begins. Elements that are appended to the array after this will not be visited bypredicate. If existing elements of the array are changed, their value as passed topredicate will be the value at the time that this operation visits them. Elements that are deleted after traversal begins and before being visited are still visited and are either looked up from the prototype or are
It performs the following steps when called:
- If
IsCallable (predicate) isfalse , throw aTypeError exception. - Ifdirection is
ascending , then - Else,
- For each
integer k ofindices, do - Return the
Record {[[Index]]:-1 𝔽,[[Value]]:undefined }.
23.1.3.13 Array.prototype.flat ( [depth ] )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - LetsourceLen be ?
LengthOfArrayLike (O). - LetdepthNum be 1.
- Ifdepth is not
undefined , then- SetdepthNum to ?
ToIntegerOrInfinity (depth). - IfdepthNum < 0, setdepthNum to 0.
- SetdepthNum to ?
- LetA be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A,O,sourceLen, 0,depthNum). - ReturnA.
23.1.3.13.1 FlattenIntoArray (target,source,sourceLen,start,depth [ ,mapperFunction [ ,thisArg ] ] )
The abstract operation FlattenIntoArray takes argumentstarget (an Object),source (an Object),sourceLen (a non-negative
Assert : IfmapperFunction is present, thenIsCallable (mapperFunction) istrue ,thisArg is present, anddepth is 1.- LettargetIndex bestart.
- LetsourceIndex be
+0 𝔽. - Repeat, while
ℝ (sourceIndex) <sourceLen,- LetP be !
ToString (sourceIndex). - Letexists be ?
HasProperty (source,P). - Ifexists is
true , then- Letelement be ?
Get (source,P). - IfmapperFunction is present, then
- Setelement to ?
Call (mapperFunction,thisArg, «element,sourceIndex,source »).
- Setelement to ?
- LetshouldFlatten be
false . - Ifdepth > 0, then
- SetshouldFlatten to ?
IsArray (element).
- SetshouldFlatten to ?
- IfshouldFlatten is
true , then- Ifdepth = +∞, letnewDepth be +∞.
- Else, letnewDepth bedepth - 1.
- LetelementLen be ?
LengthOfArrayLike (element). - SettargetIndex to ?
FlattenIntoArray (target,element,elementLen,targetIndex,newDepth).
- Else,
- IftargetIndex ≥ 253 - 1, throw a
TypeError exception. - Perform ?
CreateDataPropertyOrThrow (target, !ToString (𝔽 (targetIndex)),element). - SettargetIndex totargetIndex + 1.
- IftargetIndex ≥ 253 - 1, throw a
- Letelement be ?
- SetsourceIndex tosourceIndex +
1 𝔽.
- LetP be !
- ReturntargetIndex.
23.1.3.14 Array.prototype.flatMap (mapperFunction [ ,thisArg ] )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - LetsourceLen be ?
LengthOfArrayLike (O). - If
IsCallable (mapperFunction) isfalse , throw aTypeError exception. - LetA be ?
ArraySpeciesCreate (O, 0). - Perform ?
FlattenIntoArray (A,O,sourceLen, 0, 1,mapperFunction,thisArg). - ReturnA.
23.1.3.15 Array.prototype.forEach (callbackfn [ ,thisArg ] )
callbackfn should be a function that accepts three arguments.forEach callscallbackfn once for each element present in the array, in ascending order.callbackfn is called only for elements of the array which actually exist; it is not called for missing elements of the array.
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
forEach does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed byforEach is set before the first call tocallbackfn. Elements which are appended to the array after the call toforEach begins will not be visited bycallbackfn. If existing elements of the array are changed, their value as passed tocallbackfn will be the value at the timeforEach visits them; elements that are deleted after the call toforEach begins and before being visited are not visited.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
undefined .
This method is intentionally generic; it does not require that its
23.1.3.16 Array.prototype.includes (searchElement [ ,fromIndex ] )
This method comparessearchElement to the elements of the array, in ascending order, using the
The optional second argumentfromIndex defaults to
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Iflen = 0, return
false . - Letn be ?
ToIntegerOrInfinity (fromIndex). Assert : IffromIndex isundefined , thenn is 0.- Ifn = +∞, return
false . - Else ifn = -∞, setn to 0.
- Ifn ≥ 0, then
- Letk ben.
- Else,
- Letk belen +n.
- Ifk < 0, setk to 0.
- Repeat, whilek <len,
- LetelementK be ?
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement,elementK) istrue , returntrue . - Setk tok + 1.
- LetelementK be ?
- Return
false .
This method is intentionally generic; it does not require that its
This method intentionally differs from the similarindexOf method in two ways. First, it uses the
23.1.3.17 Array.prototype.indexOf (searchElement [ ,fromIndex ] )
This method comparessearchElement to the elements of the array, in ascending order, using the
The optional second argumentfromIndex defaults to
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Iflen = 0, return
-1 𝔽. - Letn be ?
ToIntegerOrInfinity (fromIndex). Assert : IffromIndex isundefined , thenn is 0.- Ifn = +∞, return
-1 𝔽. - Else ifn = -∞, setn to 0.
- Ifn ≥ 0, then
- Letk ben.
- Else,
- Letk belen +n.
- Ifk < 0, setk to 0.
- Repeat, whilek <len,
- LetkPresent be ?
HasProperty (O, !ToString (𝔽 (k))). - IfkPresent is
true , then- LetelementK be ?
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement,elementK) istrue , return𝔽 (k).
- LetelementK be ?
- Setk tok + 1.
- LetkPresent be ?
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.18 Array.prototype.join (separator )
This method converts the elements of the array to Strings, and then concatenates these Strings, separated by occurrences of theseparator. If no separator is provided, a single comma is used as the separator.
It performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Ifseparator is
undefined , letsep be"," . - Else, letsep be ?
ToString (separator). - LetR be the empty String.
- Letk be 0.
- Repeat, whilek <len,
- Ifk > 0, setR to the
string-concatenation ofR andsep. - Letelement be ?
Get (O, !ToString (𝔽 (k))). - Ifelement is either
undefined ornull , letnext be the empty String; otherwise, letnext be ?ToString (element). - SetR to the
string-concatenation ofR andnext. - Setk tok + 1.
- Ifk > 0, setR to the
- ReturnR.
This method is intentionally generic; it does not require that its
23.1.3.19 Array.prototype.keys ( )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Return
CreateArrayIterator (O,key ).
23.1.3.20 Array.prototype.lastIndexOf (searchElement [ ,fromIndex ] )
This method comparessearchElement to the elements of the array in descending order using the
The optional second argumentfromIndex defaults to the array's length minus one (i.e. the whole array is searched). If it is greater than or equal to the length of the array, the whole array will be searched. If it is less than
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Iflen = 0, return
-1 𝔽. - IffromIndex is present, letn be ?
ToIntegerOrInfinity (fromIndex); else letn belen - 1. - Ifn = -∞, return
-1 𝔽. - Ifn ≥ 0, then
- Letk be
min (n,len - 1).
- Letk be
- Else,
- Letk belen +n.
- Repeat, whilek ≥ 0,
- LetkPresent be ?
HasProperty (O, !ToString (𝔽 (k))). - IfkPresent is
true , then- LetelementK be ?
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement,elementK) istrue , return𝔽 (k).
- LetelementK be ?
- Setk tok - 1.
- LetkPresent be ?
- Return
-1 𝔽.
This method is intentionally generic; it does not require that its
23.1.3.21 Array.prototype.map (callbackfn [ ,thisArg ] )
callbackfn should be a function that accepts three arguments.map callscallbackfn once for each element in the array, in ascending order, and constructs a new Array from the results.callbackfn is called only for elements of the array which actually exist; it is not called for missing elements of the array.
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
map does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed bymap is set before the first call tocallbackfn. Elements which are appended to the array after the call tomap begins will not be visited bycallbackfn. If existing elements of the array are changed, their value as passed tocallbackfn will be the value at the timemap visits them; elements that are deleted after the call tomap begins and before being visited are not visited.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - LetA be ?
ArraySpeciesCreate (O,len). - Letk be 0.
- Repeat, whilek <len,
- LetPk be !
ToString (𝔽 (k)). - LetkPresent be ?
HasProperty (O,Pk). - IfkPresent is
true , then- LetkValue be ?
Get (O,Pk). - LetmappedValue be ?
Call (callbackfn,thisArg, «kValue,𝔽 (k),O »). - Perform ?
CreateDataPropertyOrThrow (A,Pk,mappedValue).
- LetkValue be ?
- Setk tok + 1.
- LetPk be !
- ReturnA.
This method is intentionally generic; it does not require that its
23.1.3.22 Array.prototype.pop ( )
This method removes the last element of the array and returns it.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Iflen = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Else,
This method is intentionally generic; it does not require that its
23.1.3.23 Array.prototype.push ( ...items )
This method appends the arguments to the end of the array, in the order in which they appear. It returns the new length of the array.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetargCount be the number of elements initems.
- Iflen +argCount > 253 - 1, throw a
TypeError exception. - For each elementE ofitems, do
- Perform ?
Set (O,"length" ,𝔽 (len),true ). - Return
𝔽 (len).
The
This method is intentionally generic; it does not require that its
23.1.3.24 Array.prototype.reduce (callbackfn [ ,initialValue ] )
callbackfn should be a function that takes four arguments.reduce calls the callback, as a function, once for each element after the first element present in the array, in ascending order.
callbackfn is called with four arguments: thepreviousValue (value from the previous call tocallbackfn), thecurrentValue (value of the current element), thecurrentIndex, and the object being traversed. The first time that callback is called, thepreviousValue andcurrentValue can be one of two values. If aninitialValue was supplied in the call toreduce, thenpreviousValue will beinitialValue andcurrentValue will be the first value in the array. If noinitialValue was supplied, thenpreviousValue will be the first value in the array andcurrentValue will be the second. It is a
reduce does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed byreduce is set before the first call tocallbackfn. Elements that are appended to the array after the call toreduce begins will not be visited bycallbackfn. If existing elements of the array are changed, their value as passed tocallbackfn will be the value at the timereduce visits them; elements that are deleted after the call toreduce begins and before being visited are not visited.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Iflen = 0 andinitialValue is not present, throw a
TypeError exception. - Letk be 0.
- Letaccumulator be
undefined . - IfinitialValue is present, then
- Setaccumulator toinitialValue.
- Else,
- LetkPresent be
false . - Repeat, whilekPresent is
false andk <len,- LetPk be !
ToString (𝔽 (k)). - SetkPresent to ?
HasProperty (O,Pk). - IfkPresent is
true , then- Setaccumulator to ?
Get (O,Pk).
- Setaccumulator to ?
- Setk tok + 1.
- LetPk be !
- IfkPresent is
false , throw aTypeError exception.
- LetkPresent be
- Repeat, whilek <len,
- Returnaccumulator.
This method is intentionally generic; it does not require that its
23.1.3.25 Array.prototype.reduceRight (callbackfn [ ,initialValue ] )
callbackfn should be a function that takes four arguments.reduceRight calls the callback, as a function, once for each element after the first element present in the array, in descending order.
callbackfn is called with four arguments: thepreviousValue (value from the previous call tocallbackfn), thecurrentValue (value of the current element), thecurrentIndex, and the object being traversed. The first time the function is called, thepreviousValue andcurrentValue can be one of two values. If aninitialValue was supplied in the call toreduceRight, thenpreviousValue will beinitialValue andcurrentValue will be the last value in the array. If noinitialValue was supplied, thenpreviousValue will be the last value in the array andcurrentValue will be the second-to-last value. It is a
reduceRight does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed byreduceRight is set before the first call tocallbackfn. Elements that are appended to the array after the call toreduceRight begins will not be visited bycallbackfn. If existing elements of the array are changed bycallbackfn, their value as passed tocallbackfn will be the value at the timereduceRight visits them; elements that are deleted after the call toreduceRight begins and before being visited are not visited.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Iflen = 0 andinitialValue is not present, throw a
TypeError exception. - Letk belen - 1.
- Letaccumulator be
undefined . - IfinitialValue is present, then
- Setaccumulator toinitialValue.
- Else,
- LetkPresent be
false . - Repeat, whilekPresent is
false andk ≥ 0,- LetPk be !
ToString (𝔽 (k)). - SetkPresent to ?
HasProperty (O,Pk). - IfkPresent is
true , then- Setaccumulator to ?
Get (O,Pk).
- Setaccumulator to ?
- Setk tok - 1.
- LetPk be !
- IfkPresent is
false , throw aTypeError exception.
- LetkPresent be
- Repeat, whilek ≥ 0,
- Returnaccumulator.
This method is intentionally generic; it does not require that its
23.1.3.26 Array.prototype.reverse ( )
This method rearranges the elements of the array so as to reverse their order. It returns the object as the result of the call.
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Letmiddle be
floor (len / 2). - Letlower be 0.
- Repeat, whilelower ≠middle,
- Letupper belen -lower - 1.
- LetupperP be !
ToString (𝔽 (upper)). - LetlowerP be !
ToString (𝔽 (lower)). - LetlowerExists be ?
HasProperty (O,lowerP). - IflowerExists is
true , then- LetlowerValue be ?
Get (O,lowerP).
- LetlowerValue be ?
- LetupperExists be ?
HasProperty (O,upperP). - IfupperExists is
true , then- LetupperValue be ?
Get (O,upperP).
- LetupperValue be ?
- IflowerExists is
true andupperExists istrue , then - Else iflowerExists is
false andupperExists istrue , then- Perform ?
Set (O,lowerP,upperValue,true ). - Perform ?
DeletePropertyOrThrow (O,upperP).
- Perform ?
- Else iflowerExists is
true andupperExists isfalse , then- Perform ?
DeletePropertyOrThrow (O,lowerP). - Perform ?
Set (O,upperP,lowerValue,true ).
- Perform ?
- Else,
Assert :lowerExists andupperExists are bothfalse .- NOTE: No action is required.
- Setlower tolower + 1.
- ReturnO.
This method is intentionally generic; it does not require that its
23.1.3.27 Array.prototype.shift ( )
This method removes the first element of the array and returns it.
It performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - Iflen = 0, then
- Perform ?
Set (O,"length" ,+0 𝔽,true ). - Return
undefined .
- Perform ?
- Letfirst be ?
Get (O,"0" ). - Letk be 1.
- Repeat, whilek <len,
- Letfrom be !
ToString (𝔽 (k)). - Letto be !
ToString (𝔽 (k - 1)). - LetfromPresent be ?
HasProperty (O,from). - IffromPresent is
true , then - Else,
Assert :fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O,to).
- Setk tok + 1.
- Letfrom be !
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (len - 1))). - Perform ?
Set (O,"length" ,𝔽 (len - 1),true ). - Returnfirst.
This method is intentionally generic; it does not require that its
23.1.3.28 Array.prototype.slice (start,end )
This method returns an array containing the elements of the array from elementstart up to, but not including, elementend (or through the end of the array ifend is
It performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letk be 0.
- Else ifrelativeStart < 0, letk be
max (len +relativeStart, 0). - Else, letk be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letfinal be 0.
- Else ifrelativeEnd < 0, letfinal be
max (len +relativeEnd, 0). - Else, letfinal be
min (relativeEnd,len). - Letcount be
max (final -k, 0). - LetA be ?
ArraySpeciesCreate (O,count). - Letn be 0.
- Repeat, whilek <final,
- LetPk be !
ToString (𝔽 (k)). - LetkPresent be ?
HasProperty (O,Pk). - IfkPresent is
true , then- LetkValue be ?
Get (O,Pk). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (n)),kValue).
- LetkValue be ?
- Setk tok + 1.
- Setn ton + 1.
- LetPk be !
- Perform ?
Set (A,"length" ,𝔽 (n),true ). - ReturnA.
The explicit setting of the
This method is intentionally generic; it does not require that its
23.1.3.29 Array.prototype.some (callbackfn [ ,thisArg ] )
callbackfn should be a function that accepts three arguments and returns a value that is coercible to a Boolean value.some callscallbackfn once for each element present in the array, in ascending order, until it finds one wherecallbackfn returnssome immediately returnssome returns
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the element, the index of the element, and the object being traversed.
some does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
The range of elements processed bysome is set before the first call tocallbackfn. Elements that are appended to the array after the call tosome begins will not be visited bycallbackfn. If existing elements of the array are changed, their value as passed tocallbackfn will be the value at the time thatsome visits them; elements that are deleted after the call tosome begins and before being visited are not visited.some acts like the "exists" quantifier in mathematics. In particular, for an empty array, it returns
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
false .
This method is intentionally generic; it does not require that its
23.1.3.30 Array.prototype.sort (comparefn )
This method sorts the elements of this array. The sort must be stable (that is, elements that compare equal must remain in their original order). Ifcomparefn is not
It performs the following steps when called:
- Ifcomparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Letobj be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (obj). - LetSortCompare be a new
Abstract Closure with parameters (x,y) that capturescomparefn and performs the following steps when called:- Return ?
CompareArrayElements (x,y,comparefn).
- Return ?
- LetsortedList be ?
SortIndexedProperties (obj,len,SortCompare,skip-holes ). - LetitemCount be the number of elements insortedList.
- Letj be 0.
- Repeat, whilej <itemCount,
- NOTE: The call to
SortIndexedProperties in step5 usesskip-holes . The remaining indices are deleted to preserve the number of holes that were detected and excluded from the sort. - Repeat, whilej <len,
- Perform ?
DeletePropertyOrThrow (obj, !ToString (𝔽 (j))). - Setj toj + 1.
- Perform ?
- Returnobj.
Because non-existent property values always compare greater than
Method calls performed by the
This method is intentionally generic; it does not require that its
23.1.3.30.1 SortIndexedProperties (obj,len,SortCompare,holes )
The abstract operation SortIndexedProperties takes argumentsobj (an Object),len (a non-negative
- Letitems be a new empty
List . - Letk be 0.
- Repeat, whilek <len,
- LetPk be !
ToString (𝔽 (k)). - Ifholes is
skip-holes , then- LetkRead be ?
HasProperty (obj,Pk).
- LetkRead be ?
- Else,
Assert :holes isread-through-holes .- LetkRead be
true .
- IfkRead is
true , then- LetkValue be ?
Get (obj,Pk). - AppendkValue toitems.
- LetkValue be ?
- Setk tok + 1.
- LetPk be !
- Sortitems using an
implementation-defined sequence ofcalls toSortCompare. If any such call returns anabrupt completion , stop before performing any further calls toSortCompare and return thatCompletion Record . - Returnitems.
Thesort order is the ordering ofitems after completion of step
Unless the
- There must be some mathematical permutation π of the non-negative
integers less thanitemCount, such that for every non-negativeinteger j less thanitemCount, the elementold[j] is exactly the same asnew[π(j)] . - Then for all non-negative
integers j andk, each less thanitemCount, ifℝ (SortCompare(old[j], old[k])) < 0π(j) < π(k) .
Here the notation
An abstract closure or functioncomparator is aconsistent comparator for a set of valuesS if all of the requirements below are met for all valuesa,b, andc (possibly the same value) in the setS: The notation
- Callingcomparator(a,b) always returns the same valuev when given a specific pair of valuesa andb as its two arguments. Furthermore,v
is a Number , andv is notNaN . Note that this implies that exactly one ofa <Cb,a =Cb, anda >Cb will be true for a given pair ofa andb. - Callingcomparator(a,b) does not modifyobj or any object onobj's prototype chain.
- a =Ca (reflexivity)
- Ifa =Cb, thenb =Ca (symmetry)
- Ifa =Cb andb =Cc, thena =Cc (transitivity of =C)
- Ifa <Cb andb <Cc, thena <Cc (transitivity of <C)
- Ifa >Cb andb >Cc, thena >Cc (transitivity of >C)
The above conditions are necessary and sufficient to ensure thatcomparator divides the setS into equivalence classes and that these equivalence classes are totally ordered.
23.1.3.30.2 CompareArrayElements (x,y,comparefn )
The abstract operation CompareArrayElements takes argumentsx (an
- Ifx andy are both
undefined , return+0 𝔽. - Ifx is
undefined , return1 𝔽. - Ify is
undefined , return-1 𝔽. - Ifcomparefn is not
undefined , then - LetxString be ?
ToString (x). - LetyString be ?
ToString (y). - LetxSmaller be !
IsLessThan (xString,yString,true ). - IfxSmaller is
true , return-1 𝔽. - LetySmaller be !
IsLessThan (yString,xString,true ). - IfySmaller is
true , return1 𝔽. - Return
+0 𝔽.
23.1.3.31 Array.prototype.splice (start,deleteCount, ...items )
This method deletes thedeleteCount elements of the array starting at
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letactualStart be 0.
- Else ifrelativeStart < 0, letactualStart be
max (len +relativeStart, 0). - Else, letactualStart be
min (relativeStart,len). - LetitemCount be the number of elements initems.
- Ifstart is not present, then
- LetactualDeleteCount be 0.
- Else ifdeleteCount is not present, then
- LetactualDeleteCount belen -actualStart.
- Else,
- Letdc be ?
ToIntegerOrInfinity (deleteCount). - LetactualDeleteCount be the result of
clamping dc between 0 andlen -actualStart.
- Letdc be ?
- Iflen +itemCount -actualDeleteCount > 253 - 1, throw a
TypeError exception. - LetA be ?
ArraySpeciesCreate (O,actualDeleteCount). - Letk be 0.
- Repeat, whilek <actualDeleteCount,
- Letfrom be !
ToString (𝔽 (actualStart +k)). - If ?
HasProperty (O,from) istrue , then- LetfromValue be ?
Get (O,from). - Perform ?
CreateDataPropertyOrThrow (A, !ToString (𝔽 (k)),fromValue).
- LetfromValue be ?
- Setk tok + 1.
- Letfrom be !
- Perform ?
Set (A,"length" ,𝔽 (actualDeleteCount),true ). - IfitemCount <actualDeleteCount, then
- Setk toactualStart.
- Repeat, whilek < (len -actualDeleteCount),
- Letfrom be !
ToString (𝔽 (k +actualDeleteCount)). - Letto be !
ToString (𝔽 (k +itemCount)). - If ?
HasProperty (O,from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O,to).
- Perform ?
- Setk tok + 1.
- Letfrom be !
- Setk tolen.
- Repeat, whilek > (len -actualDeleteCount +itemCount),
- Perform ?
DeletePropertyOrThrow (O, !ToString (𝔽 (k - 1))). - Setk tok - 1.
- Perform ?
- Else ifitemCount >actualDeleteCount, then
- Setk to (len -actualDeleteCount).
- Repeat, whilek >actualStart,
- Letfrom be !
ToString (𝔽 (k +actualDeleteCount - 1)). - Letto be !
ToString (𝔽 (k +itemCount - 1)). - If ?
HasProperty (O,from) istrue , then - Else,
- Perform ?
DeletePropertyOrThrow (O,to).
- Perform ?
- Setk tok - 1.
- Letfrom be !
- Setk toactualStart.
- For each elementE ofitems, do
- Perform ?
Set (O,"length" ,𝔽 (len -actualDeleteCount +itemCount),true ). - ReturnA.
This method is intentionally generic; it does not require that its
23.1.3.32 Array.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
An ECMAScript implementation that includes the ECMA-402 Internationalization API must implement this method as specified in the ECMA-402 specification. If an ECMAScript implementation does not include the ECMA-402 API the following specification of this method is used.
The first edition of ECMA-402 did not include a replacement specification for this method.
The meanings of the optional parameters to this method are defined in the ECMA-402 specification; implementations that do not include ECMA-402 support must not use those parameter positions for anything else.
This method performs the following steps when called:
- Letarray be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (array). - Letseparator be the
implementation-defined list-separator String value appropriate for thehost environment 's current locale (such as", " ). - LetR be the empty String.
- Letk be 0.
- Repeat, whilek <len,
- Ifk > 0, then
- SetR to the
string-concatenation ofR andseparator.
- SetR to the
- LetnextElement be ?
Get (array, !ToString (𝔽 (k))). - IfnextElement is neither
undefined nornull , then- LetS be ?
ToString (?Invoke (nextElement,"toLocaleString" )). - SetR to the
string-concatenation ofR andS.
- LetS be ?
- Setk tok + 1.
- Ifk > 0, then
- ReturnR.
This method converts the elements of the array to Strings using theirtoLocaleString methods, and then concatenates these Strings, separated by occurrences of antoString except that it is intended to yield a locale-sensitive result corresponding with conventions of the
This method is intentionally generic; it does not require that its
23.1.3.33 Array.prototype.toReversed ( )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetA be ?
ArrayCreate (len). - Letk be 0.
- Repeat, whilek <len,
- ReturnA.
23.1.3.34 Array.prototype.toSorted (comparefn )
This method performs the following steps when called:
- Ifcomparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetA be ?
ArrayCreate (len). - LetSortCompare be a new
Abstract Closure with parameters (x,y) that capturescomparefn and performs the following steps when called:- Return ?
CompareArrayElements (x,y,comparefn).
- Return ?
- LetsortedList be ?
SortIndexedProperties (O,len,SortCompare,read-through-holes ). - Letj be 0.
- Repeat, whilej <len,
- Perform !
CreateDataPropertyOrThrow (A, !ToString (𝔽 (j)),sortedList[j]). - Setj toj + 1.
- Perform !
- ReturnA.
23.1.3.35 Array.prototype.toSpliced (start,skipCount, ...items )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart is -∞, letactualStart be 0.
- Else ifrelativeStart < 0, letactualStart be
max (len +relativeStart, 0). - Else, letactualStart be
min (relativeStart,len). - LetinsertCount be the number of elements initems.
- Ifstart is not present, then
- LetactualSkipCount be 0.
- Else ifskipCount is not present, then
- LetactualSkipCount belen -actualStart.
- Else,
- Letsc be ?
ToIntegerOrInfinity (skipCount). - LetactualSkipCount be the result of
clamping sc between 0 andlen -actualStart.
- Letsc be ?
- LetnewLen belen +insertCount -actualSkipCount.
- IfnewLen > 253 - 1, throw a
TypeError exception. - LetA be ?
ArrayCreate (newLen). - Leti be 0.
- Letr beactualStart +actualSkipCount.
- Repeat, whilei <actualStart,
- LetPi be !
ToString (𝔽 (i)). - LetiValue be ?
Get (O,Pi). - Perform !
CreateDataPropertyOrThrow (A,Pi,iValue). - Seti toi + 1.
- LetPi be !
- For each elementE ofitems, do
- LetPi be !
ToString (𝔽 (i)). - Perform !
CreateDataPropertyOrThrow (A,Pi,E). - Seti toi + 1.
- LetPi be !
- Repeat, whilei <newLen,
- ReturnA.
23.1.3.36 Array.prototype.toString ( )
This method performs the following steps when called:
- Letarray be ?
ToObject (this value). - Letfunc be ?
Get (array,"join" ). - If
IsCallable (func) isfalse , setfunc to the intrinsic function %Object.prototype.toString%. - Return ?
Call (func,array).
This method is intentionally generic; it does not require that its
23.1.3.37 Array.prototype.unshift ( ...items )
This method prepends the arguments to the start of the array, such that their order within the array is the same as the order in which they appear in the argument list.
It performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetargCount be the number of elements initems.
- IfargCount > 0, then
- Iflen +argCount > 253 - 1, throw a
TypeError exception. - Letk belen.
- Repeat, whilek > 0,
- Letfrom be !
ToString (𝔽 (k - 1)). - Letto be !
ToString (𝔽 (k +argCount - 1)). - LetfromPresent be ?
HasProperty (O,from). - IffromPresent is
true , then - Else,
Assert :fromPresent isfalse .- Perform ?
DeletePropertyOrThrow (O,to).
- Setk tok - 1.
- Letfrom be !
- Letj be
+0 𝔽. - For each elementE ofitems, do
- Iflen +argCount > 253 - 1, throw a
- Perform ?
Set (O,"length" ,𝔽 (len +argCount),true ). - Return
𝔽 (len +argCount).
The
This method is intentionally generic; it does not require that its
23.1.3.38 Array.prototype.values ( )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Return
CreateArrayIterator (O,value ).
23.1.3.39 Array.prototype.with (index,value )
This method performs the following steps when called:
- LetO be ?
ToObject (this value). - Letlen be ?
LengthOfArrayLike (O). - LetrelativeIndex be ?
ToIntegerOrInfinity (index). - IfrelativeIndex ≥ 0, letactualIndex berelativeIndex.
- Else, letactualIndex belen +relativeIndex.
- IfactualIndex ≥len oractualIndex < 0, throw a
RangeError exception. - LetA be ?
ArrayCreate (len). - Letk be 0.
- Repeat, whilek <len,
- LetPk be !
ToString (𝔽 (k)). - Ifk isactualIndex, letfromValue bevalue.
- Else, letfromValue be ?
Get (O,Pk). - Perform !
CreateDataPropertyOrThrow (A,Pk,fromValue). - Setk tok + 1.
- LetPk be !
- ReturnA.
23.1.3.40 Array.prototype [ @@iterator ] ( )
The initial value of the
23.1.3.41 Array.prototype [ @@unscopables ]
The initial value of the
- LetunscopableList be
OrdinaryObjectCreate (null ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"at" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"copyWithin" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"entries" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"fill" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"find" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLast" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"findLastIndex" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flat" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"flatMap" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"includes" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"keys" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toReversed" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSorted" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"toSpliced" ,true ). - Perform !
CreateDataPropertyOrThrow (unscopableList,"values" ,true ). - ReturnunscopableList.
This property has the attributes {[[Writable]]:
The own property names of this object are property names that were not included as standard properties ofArray.prototype prior to the ECMAScript 2015 specification. These names are ignored forwith statement binding purposes in order to preserve the behaviour of existing code that might use one of these names as a binding in an outer scope that is shadowed by awith statement whose binding object is an Array.
The reason that
23.1.4 Properties of Array Instances
Array instances are
Array instances have a
23.1.4.1 length
The
The
Reducing the value of the
23.1.5 Array Iterator Objects
An Array Iterator is an object, that represents a specific iteration over some specific Array instance object. There is not a named
23.1.5.1 CreateArrayIterator (array,kind )
The abstract operation CreateArrayIterator takes argumentsarray (an Object) andkind (
- Letclosure be a new
Abstract Closure with no parameters that captureskind andarray and performs the following steps when called:- Letindex be 0.
- Repeat,
- Ifarray has a[[TypedArrayName]] internal slot, then
- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (array,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Letlen be
TypedArrayLength (taRecord).
- LettaRecord be
- Else,
- Letlen be ?
LengthOfArrayLike (array).
- Letlen be ?
- Ifindex ≥len, return
NormalCompletion (undefined ). - LetindexNumber be
𝔽 (index). - Ifkind is
key , then- Letresult beindexNumber.
- Else,
- LetelementKey be !
ToString (indexNumber). - LetelementValue be ?
Get (array,elementKey). - Ifkind is
value , then- Letresult beelementValue.
- Else,
Assert :kind iskey+value .- Letresult be
CreateArrayFromList («indexNumber,elementValue »).
- LetelementKey be !
- Perform ?
GeneratorYield (CreateIterResultObject (result,false )). - Setindex toindex + 1.
- Ifarray has a[[TypedArrayName]] internal slot, then
- Return
CreateIteratorFromClosure (closure,"%ArrayIteratorPrototype%" ,%ArrayIteratorPrototype% ).
23.1.5.2 The %ArrayIteratorPrototype% Object
The%ArrayIteratorPrototype% object:
- has properties that are inherited by all Array Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
23.1.5.2.1 %ArrayIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%ArrayIteratorPrototype%" ).
23.1.5.2.2 %ArrayIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
23.2 TypedArray Objects
ATypedArray presents an array-like view of an underlying binary data buffer (
| Element Type | Element Size | Conversion Operation | Description | |
|---|---|---|---|---|
| Int8Array %Int8Array% | 1 | 8-bit two's complement signed | ||
| Uint8Array %Uint8Array% | 1 | 8-bit unsigned | ||
| Uint8ClampedArray %Uint8ClampedArray% | 1 | 8-bit unsigned | ||
| Int16Array %Int16Array% | 2 | 16-bit two's complement signed | ||
| Uint16Array %Uint16Array% | 2 | 16-bit unsigned | ||
| Int32Array %Int32Array% | 4 | 32-bit two's complement signed | ||
| Uint32Array %Uint32Array% | 4 | 32-bit unsigned | ||
| BigInt64Array %BigInt64Array% | 8 | 64-bit two's complement signed | ||
| BigUint64Array %BigUint64Array% | 8 | 64-bit unsigned | ||
| Float32Array %Float32Array% | 4 | 32-bit IEEE floating point | ||
| Float64Array %Float64Array% | 8 | 64-bit IEEE floating point |
In the definitions below, references toTypedArray should be replaced with the appropriate
23.2.1 The %TypedArray% Intrinsic Object
The%TypedArray% intrinsic object:
- is a
constructor function object that all of theTypedArrayconstructor objects inherit from. - along with its corresponding prototype object, provides common properties that are inherited by allTypedArray
constructors and their instances. - does not have a global name or appear as a property of the
global object . - acts as the abstract superclass of the variousTypedArray
constructors . - will throw an error when invoked, because it is an abstract class
constructor . TheTypedArrayconstructors do not perform asupercall to it.
23.2.1.1 %TypedArray% ( )
This function performs the following steps when called:
- Throw a
TypeError exception.
The
23.2.2 Properties of the %TypedArray% Intrinsic Object
The
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has a
"name" property whose value is"TypedArray" . - has the following properties:
23.2.2.1 %TypedArray%.from (source [ ,mapfn [ ,thisArg ] ] )
This method performs the following steps when called:
- LetC be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - Ifmapfn is
undefined , then- Letmapping be
false .
- Letmapping be
- Else,
- If
IsCallable (mapfn) isfalse , throw aTypeError exception. - Letmapping be
true .
- If
- LetusingIterator be ?
GetMethod (source,@@iterator ). - IfusingIterator is not
undefined , then- Letvalues be ?
IteratorToList (?GetIteratorFromMethod (source,usingIterator)). - Letlen be the number of elements invalues.
- LettargetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Letk be 0.
- Repeat, whilek <len,
Assert :values is now an emptyList .- ReturntargetObj.
- Letvalues be ?
- NOTE:source is not an Iterable so assume it is already an
array-like object . - LetarrayLike be !
ToObject (source). - Letlen be ?
LengthOfArrayLike (arrayLike). - LettargetObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Letk be 0.
- Repeat, whilek <len,
- ReturntargetObj.
23.2.2.2 %TypedArray%.of ( ...items )
This method performs the following steps when called:
- Letlen be the number of elements initems.
- LetC be the
this value. - If
IsConstructor (C) isfalse , throw aTypeError exception. - LetnewObj be ?
TypedArrayCreateFromConstructor (C, «𝔽 (len) »). - Letk be 0.
- Repeat, whilek <len,
- ReturnnewObj.
23.2.2.3 %TypedArray%.prototype
The initial value of.prototype is the
This property has the attributes {[[Writable]]:
23.2.2.4 get %TypedArray% [ @@species ]
[@@species] is an
- Return the
this value.
The value of the
23.2.3 Properties of the %TypedArray% Prototype Object
The%TypedArray% prototype object:
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is%TypedArray.prototype%.
- is an
ordinary object . - does not have a[[ViewedArrayBuffer]] or any other of the internal slots that are specific toTypedArray instance objects.
23.2.3.1 %TypedArray%.prototype.at (index )
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetrelativeIndex be ?
ToIntegerOrInfinity (index). - IfrelativeIndex ≥ 0, then
- Letk berelativeIndex.
- Else,
- Letk belen +relativeIndex.
- Ifk < 0 ork ≥len, return
undefined . - Return !
Get (O, !ToString (𝔽 (k))).
23.2.3.2 get %TypedArray%.prototype.buffer
.prototype.buffer is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- Letbuffer beO.[[ViewedArrayBuffer]].
- Returnbuffer.
23.2.3.3 get %TypedArray%.prototype.byteLength
.prototype.byteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - Letsize be
TypedArrayByteLength (taRecord). - Return
𝔽 (size).
23.2.3.4 get %TypedArray%.prototype.byteOffset
.prototype.byteOffset is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Letoffset beO.[[ByteOffset]].
- Return
𝔽 (offset).
23.2.3.5 %TypedArray%.prototype.constructor
The initial value of.prototype.constructor is
23.2.3.6 %TypedArray%.prototype.copyWithin (target,start [ ,end ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.copyWithin as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetrelativeTarget be ?
ToIntegerOrInfinity (target). - IfrelativeTarget = -∞, lettargetIndex be 0.
- Else ifrelativeTarget < 0, lettargetIndex be
max (len +relativeTarget, 0). - Else, lettargetIndex be
min (relativeTarget,len). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letstartIndex be 0.
- Else ifrelativeStart < 0, letstartIndex be
max (len +relativeStart, 0). - Else, letstartIndex be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letendIndex be 0.
- Else ifrelativeEnd < 0, letendIndex be
max (len +relativeEnd, 0). - Else, letendIndex be
min (relativeEnd,len). - Letcount be
min (endIndex -startIndex,len -targetIndex). - Ifcount > 0, then
- NOTE: The copying must be performed in a manner that preserves the bit-level encoding of the source data.
- Letbuffer beO.[[ViewedArrayBuffer]].
- SettaRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Setlen to
TypedArrayLength (taRecord). - LetelementSize be
TypedArrayElementSize (O). - LetbyteOffset beO.[[ByteOffset]].
- LetbufferByteLimit be (len ×elementSize) +byteOffset.
- LettoByteIndex be (targetIndex ×elementSize) +byteOffset.
- LetfromByteIndex be (startIndex ×elementSize) +byteOffset.
- LetcountBytes becount ×elementSize.
- IffromByteIndex <toByteIndex andtoByteIndex <fromByteIndex +countBytes, then
- Letdirection be -1.
- SetfromByteIndex tofromByteIndex +countBytes - 1.
- SettoByteIndex totoByteIndex +countBytes - 1.
- Else,
- Letdirection be 1.
- Repeat, whilecountBytes > 0,
- IffromByteIndex <bufferByteLimit andtoByteIndex <bufferByteLimit, then
- Letvalue be
GetValueFromBuffer (buffer,fromByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (buffer,toByteIndex,uint8 ,value,true ,unordered ). - SetfromByteIndex tofromByteIndex +direction.
- SettoByteIndex totoByteIndex +direction.
- SetcountBytes tocountBytes - 1.
- Letvalue be
- Else,
- SetcountBytes to 0.
- IffromByteIndex <bufferByteLimit andtoByteIndex <bufferByteLimit, then
- ReturnO.
23.2.3.7 %TypedArray%.prototype.entries ( )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key+value ).
23.2.3.8 %TypedArray%.prototype.every (callbackfn [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.every as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
true .
This method is not generic. The
23.2.3.9 %TypedArray%.prototype.fill (value [ ,start [ ,end ] ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.fill as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - IfO.[[ContentType]] is
bigint , setvalue to ?ToBigInt (value). - Otherwise, setvalue to ?
ToNumber (value). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letstartIndex be 0.
- Else ifrelativeStart < 0, letstartIndex be
max (len +relativeStart, 0). - Else, letstartIndex be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letendIndex be 0.
- Else ifrelativeEnd < 0, letendIndex be
max (len +relativeEnd, 0). - Else, letendIndex be
min (relativeEnd,len). - SettaRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Setlen to
TypedArrayLength (taRecord). - SetendIndex to
min (endIndex,len). - Letk bestartIndex.
- Repeat, whilek <endIndex,
- ReturnO.
23.2.3.10 %TypedArray%.prototype.filter (callbackfn [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.filter as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letkept be a new empty
List . - Letcaptured be 0.
- Letk be 0.
- Repeat, whilek <len,
- LetA be ?
TypedArraySpeciesCreate (O, «𝔽 (captured) »). - Letn be 0.
- For each elemente ofkept, do
- ReturnA.
This method is not generic. The
23.2.3.11 %TypedArray%.prototype.find (predicate [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.find as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetfindRec be ?
FindViaPredicate (O,len,ascending ,predicate,thisArg). - ReturnfindRec.[[Value]].
This method is not generic. The
23.2.3.12 %TypedArray%.prototype.findIndex (predicate [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.findIndex as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetfindRec be ?
FindViaPredicate (O,len,ascending ,predicate,thisArg). - ReturnfindRec.[[Index]].
This method is not generic. The
23.2.3.13 %TypedArray%.prototype.findLast (predicate [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.findLast as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetfindRec be ?
FindViaPredicate (O,len,descending ,predicate,thisArg). - ReturnfindRec.[[Value]].
This method is not generic. The
23.2.3.14 %TypedArray%.prototype.findLastIndex (predicate [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.findLastIndex as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetfindRec be ?
FindViaPredicate (O,len,descending ,predicate,thisArg). - ReturnfindRec.[[Index]].
This method is not generic. The
23.2.3.15 %TypedArray%.prototype.forEach (callbackfn [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.forEach as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
undefined .
This method is not generic. The
23.2.3.16 %TypedArray%.prototype.includes (searchElement [ ,fromIndex ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.includes as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - Iflen = 0, return
false . - Letn be ?
ToIntegerOrInfinity (fromIndex). Assert : IffromIndex isundefined , thenn is 0.- Ifn = +∞, return
false . - Else ifn = -∞, setn to 0.
- Ifn ≥ 0, then
- Letk ben.
- Else,
- Letk belen +n.
- Ifk < 0, setk to 0.
- Repeat, whilek <len,
- LetelementK be !
Get (O, !ToString (𝔽 (k))). - If
SameValueZero (searchElement,elementK) istrue , returntrue . - Setk tok + 1.
- LetelementK be !
- Return
false .
This method is not generic. The
23.2.3.17 %TypedArray%.prototype.indexOf (searchElement [ ,fromIndex ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.indexOf as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - Iflen = 0, return
-1 𝔽. - Letn be ?
ToIntegerOrInfinity (fromIndex). Assert : IffromIndex isundefined , thenn is 0.- Ifn = +∞, return
-1 𝔽. - Else ifn = -∞, setn to 0.
- Ifn ≥ 0, then
- Letk ben.
- Else,
- Letk belen +n.
- Ifk < 0, setk to 0.
- Repeat, whilek <len,
- LetkPresent be !
HasProperty (O, !ToString (𝔽 (k))). - IfkPresent is
true , then- LetelementK be !
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement,elementK) istrue , return𝔽 (k).
- LetelementK be !
- Setk tok + 1.
- LetkPresent be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.18 %TypedArray%.prototype.join (separator )
The interpretation and use of the arguments of this method are the same as forArray.prototype.join as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - Ifseparator is
undefined , letsep be"," . - Else, letsep be ?
ToString (separator). - LetR be the empty String.
- Letk be 0.
- Repeat, whilek <len,
- Ifk > 0, setR to the
string-concatenation ofR andsep. - Letelement be !
Get (O, !ToString (𝔽 (k))). - Ifelement is
undefined , letnext be the empty String; otherwise, letnext be !ToString (element). - SetR to the
string-concatenation ofR andnext. - Setk tok + 1.
- Ifk > 0, setR to the
- ReturnR.
This method is not generic. The
23.2.3.19 %TypedArray%.prototype.keys ( )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,key ).
23.2.3.20 %TypedArray%.prototype.lastIndexOf (searchElement [ ,fromIndex ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.lastIndexOf as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - Iflen = 0, return
-1 𝔽. - IffromIndex is present, letn be ?
ToIntegerOrInfinity (fromIndex); else letn belen - 1. - Ifn = -∞, return
-1 𝔽. - Ifn ≥ 0, then
- Letk be
min (n,len - 1).
- Letk be
- Else,
- Letk belen +n.
- Repeat, whilek ≥ 0,
- LetkPresent be !
HasProperty (O, !ToString (𝔽 (k))). - IfkPresent is
true , then- LetelementK be !
Get (O, !ToString (𝔽 (k))). - If
IsStrictlyEqual (searchElement,elementK) istrue , return𝔽 (k).
- LetelementK be !
- Setk tok - 1.
- LetkPresent be !
- Return
-1 𝔽.
This method is not generic. The
23.2.3.21 get %TypedArray%.prototype.length
.prototype.length is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has[[ViewedArrayBuffer]] and[[ArrayLength]] internal slots.- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , return+0 𝔽. - Letlength be
TypedArrayLength (taRecord). - Return
𝔽 (length).
This function is not generic. The
23.2.3.22 %TypedArray%.prototype.map (callbackfn [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.map as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - LetA be ?
TypedArraySpeciesCreate (O, «𝔽 (len) »). - Letk be 0.
- Repeat, whilek <len,
- ReturnA.
This method is not generic. The
23.2.3.23 %TypedArray%.prototype.reduce (callbackfn [ ,initialValue ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.reduce as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Iflen = 0 andinitialValue is not present, throw a
TypeError exception. - Letk be 0.
- Letaccumulator be
undefined . - IfinitialValue is present, then
- Setaccumulator toinitialValue.
- Else,
- Repeat, whilek <len,
- Returnaccumulator.
This method is not generic. The
23.2.3.24 %TypedArray%.prototype.reduceRight (callbackfn [ ,initialValue ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.reduceRight as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Iflen = 0 andinitialValue is not present, throw a
TypeError exception. - Letk belen - 1.
- Letaccumulator be
undefined . - IfinitialValue is present, then
- Setaccumulator toinitialValue.
- Else,
- Repeat, whilek ≥ 0,
- Returnaccumulator.
This method is not generic. The
23.2.3.25 %TypedArray%.prototype.reverse ( )
The interpretation and use of the arguments of this method are the same as forArray.prototype.reverse as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - Letmiddle be
floor (len / 2). - Letlower be 0.
- Repeat, whilelower ≠middle,
- ReturnO.
This method is not generic. The
23.2.3.26 %TypedArray%.prototype.set (source [ ,offset ] )
This method sets multiple values in thisTypedArray, reading the values fromsource. The details differ based upon the type ofsource. The optionaloffset value indicates the first element index in thisTypedArray where values are written. If omitted, it is assumed to be 0.
It performs the following steps when called:
- Lettarget be the
this value. - Perform ?
RequireInternalSlot (target,[[TypedArrayName]]). Assert :target has a[[ViewedArrayBuffer]] internal slot.- LettargetOffset be ?
ToIntegerOrInfinity (offset). - IftargetOffset < 0, throw a
RangeError exception. - Ifsource
is an Object that has a[[TypedArrayName]] internal slot, then- Perform ?
SetTypedArrayFromTypedArray (target,targetOffset,source).
- Perform ?
- Else,
- Perform ?
SetTypedArrayFromArrayLike (target,targetOffset,source).
- Perform ?
- Return
undefined .
This method is not generic. The
23.2.3.26.1 SetTypedArrayFromTypedArray (target,targetOffset,source )
The abstract operation SetTypedArrayFromTypedArray takes argumentstarget (a
- LettargetBuffer betarget.[[ViewedArrayBuffer]].
- LettargetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - LettargetLength be
TypedArrayLength (targetRecord). - LetsrcBuffer besource.[[ViewedArrayBuffer]].
- LetsrcRecord be
MakeTypedArrayWithBufferWitnessRecord (source,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - LetsrcLength be
TypedArrayLength (srcRecord). - LettargetType be
TypedArrayElementType (target). - LettargetElementSize be
TypedArrayElementSize (target). - LettargetByteOffset betarget.[[ByteOffset]].
- LetsrcType be
TypedArrayElementType (source). - LetsrcElementSize be
TypedArrayElementSize (source). - LetsrcByteOffset besource.[[ByteOffset]].
- IftargetOffset = +∞, throw a
RangeError exception. - IfsrcLength +targetOffset >targetLength, throw a
RangeError exception. - Iftarget.[[ContentType]] is notsource.[[ContentType]], throw a
TypeError exception. - If
IsSharedArrayBuffer (srcBuffer) istrue ,IsSharedArrayBuffer (targetBuffer) istrue , andsrcBuffer.[[ArrayBufferData]] istargetBuffer.[[ArrayBufferData]], letsameSharedArrayBuffer betrue ; otherwise, letsameSharedArrayBuffer befalse . - If
SameValue (srcBuffer,targetBuffer) istrue orsameSharedArrayBuffer istrue , then- LetsrcByteLength be
TypedArrayByteLength (srcRecord). - SetsrcBuffer to ?
CloneArrayBuffer (srcBuffer,srcByteOffset,srcByteLength). - LetsrcByteIndex be 0.
- LetsrcByteLength be
- Else,
- LetsrcByteIndex besrcByteOffset.
- LettargetByteIndex be (targetOffset ×targetElementSize) +targetByteOffset.
- Letlimit betargetByteIndex + (targetElementSize ×srcLength).
- IfsrcType istargetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- Repeat, whiletargetByteIndex <limit,
- Letvalue be
GetValueFromBuffer (srcBuffer,srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer,targetByteIndex,uint8 ,value,true ,unordered ). - SetsrcByteIndex tosrcByteIndex + 1.
- SettargetByteIndex totargetByteIndex + 1.
- Letvalue be
- Else,
- Repeat, whiletargetByteIndex <limit,
- Letvalue be
GetValueFromBuffer (srcBuffer,srcByteIndex,srcType,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer,targetByteIndex,targetType,value,true ,unordered ). - SetsrcByteIndex tosrcByteIndex +srcElementSize.
- SettargetByteIndex totargetByteIndex +targetElementSize.
- Letvalue be
- Repeat, whiletargetByteIndex <limit,
- Return
unused .
23.2.3.26.2 SetTypedArrayFromArrayLike (target,targetOffset,source )
The abstract operation SetTypedArrayFromArrayLike takes argumentstarget (a
- LettargetRecord be
MakeTypedArrayWithBufferWitnessRecord (target,seq-cst ). - If
IsTypedArrayOutOfBounds (targetRecord) istrue , throw aTypeError exception. - LettargetLength be
TypedArrayLength (targetRecord). - Letsrc be ?
ToObject (source). - LetsrcLength be ?
LengthOfArrayLike (src). - IftargetOffset = +∞, throw a
RangeError exception. - IfsrcLength +targetOffset >targetLength, throw a
RangeError exception. - Letk be 0.
- Repeat, whilek <srcLength,
- LetPk be !
ToString (𝔽 (k)). - Letvalue be ?
Get (src,Pk). - LettargetIndex be
𝔽 (targetOffset +k). - Perform ?
TypedArraySetElement (target,targetIndex,value). - Setk tok + 1.
- LetPk be !
- Return
unused .
23.2.3.27 %TypedArray%.prototype.slice (start,end )
The interpretation and use of the arguments of this method are the same as forArray.prototype.slice as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - LetsrcArrayLength be
TypedArrayLength (taRecord). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letstartIndex be 0.
- Else ifrelativeStart < 0, letstartIndex be
max (srcArrayLength +relativeStart, 0). - Else, letstartIndex be
min (relativeStart,srcArrayLength). - Ifend is
undefined , letrelativeEnd besrcArrayLength; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letendIndex be 0.
- Else ifrelativeEnd < 0, letendIndex be
max (srcArrayLength +relativeEnd, 0). - Else, letendIndex be
min (relativeEnd,srcArrayLength). - LetcountBytes be
max (endIndex -startIndex, 0). - LetA be ?
TypedArraySpeciesCreate (O, «𝔽 (countBytes) »). - IfcountBytes > 0, then
- SettaRecord to
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - SetendIndex to
min (endIndex,TypedArrayLength (taRecord)). - SetcountBytes to
max (endIndex -startIndex, 0). - LetsrcType be
TypedArrayElementType (O). - LettargetType be
TypedArrayElementType (A). - IfsrcType istargetType, then
- NOTE: The transfer must be performed in a manner that preserves the bit-level encoding of the source data.
- LetsrcBuffer beO.[[ViewedArrayBuffer]].
- LettargetBuffer beA.[[ViewedArrayBuffer]].
- LetelementSize be
TypedArrayElementSize (O). - LetsrcByteOffset beO.[[ByteOffset]].
- LetsrcByteIndex be (startIndex ×elementSize) +srcByteOffset.
- LettargetByteIndex beA.[[ByteOffset]].
- LetendByteIndex betargetByteIndex + (countBytes ×elementSize).
- Repeat, whiletargetByteIndex <endByteIndex,
- Letvalue be
GetValueFromBuffer (srcBuffer,srcByteIndex,uint8 ,true ,unordered ). - Perform
SetValueInBuffer (targetBuffer,targetByteIndex,uint8 ,value,true ,unordered ). - SetsrcByteIndex tosrcByteIndex + 1.
- SettargetByteIndex totargetByteIndex + 1.
- Letvalue be
- Else,
- SettaRecord to
- ReturnA.
This method is not generic. The
23.2.3.28 %TypedArray%.prototype.some (callbackfn [ ,thisArg ] )
The interpretation and use of the arguments of this method are the same as forArray.prototype.some as defined in
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letk be 0.
- Repeat, whilek <len,
- Return
false .
This method is not generic. The
23.2.3.29 %TypedArray%.prototype.sort (comparefn )
This is a distinct method that, except as described below, implements the same requirements as those ofArray.prototype.sort as defined in
This method is not generic. The
It performs the following steps when called:
- Ifcomparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - Letobj be the
this value. - LettaRecord be ?
ValidateTypedArray (obj,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - NOTE: The following closure performs a numeric comparison rather than the string comparison used in
23.1.3.30 . - LetSortCompare be a new
Abstract Closure with parameters (x,y) that capturescomparefn and performs the following steps when called:- Return ?
CompareTypedArrayElements (x,y,comparefn).
- Return ?
- LetsortedList be ?
SortIndexedProperties (obj,len,SortCompare,read-through-holes ). - Letj be 0.
- Repeat, whilej <len,
- Returnobj.
Because
23.2.3.30 %TypedArray%.prototype.subarray (start,end )
This method returns a newTypedArray whose element type is the element type of thisTypedArray and whose ArrayBuffer is the ArrayBuffer of thisTypedArray, referencing the elements in the
It performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- Letbuffer beO.[[ViewedArrayBuffer]].
- LetsrcRecord be
MakeTypedArrayWithBufferWitnessRecord (O,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , then- LetsrcLength be 0.
- Else,
- LetsrcLength be
TypedArrayLength (srcRecord).
- LetsrcLength be
- LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letstartIndex be 0.
- Else ifrelativeStart < 0, letstartIndex be
max (srcLength +relativeStart, 0). - Else, letstartIndex be
min (relativeStart,srcLength). - LetelementSize be
TypedArrayElementSize (O). - LetsrcByteOffset beO.[[ByteOffset]].
- LetbeginByteOffset besrcByteOffset + (startIndex ×elementSize).
- IfO.[[ArrayLength]] is
auto andend isundefined , then- LetargumentsList be «buffer,
𝔽 (beginByteOffset) ».
- LetargumentsList be «buffer,
- Else,
- Ifend is
undefined , letrelativeEnd besrcLength; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letendIndex be 0.
- Else ifrelativeEnd < 0, letendIndex be
max (srcLength +relativeEnd, 0). - Else, letendIndex be
min (relativeEnd,srcLength). - LetnewLength be
max (endIndex -startIndex, 0). - LetargumentsList be «buffer,
𝔽 (beginByteOffset),𝔽 (newLength) ».
- Ifend is
- Return ?
TypedArraySpeciesCreate (O,argumentsList).
This method is not generic. The
23.2.3.31 %TypedArray%.prototype.toLocaleString ( [reserved1 [ ,reserved2 ] ] )
This is a distinct method that implements the same algorithm asArray.prototype.toLocaleString as defined in
This method is not generic.
If the ECMAScript implementation includes the ECMA-402 Internationalization API this method is based upon the algorithm forArray.prototype.toLocaleString that is in the ECMA-402 specification.
23.2.3.32 %TypedArray%.prototype.toReversed ( )
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlength be
TypedArrayLength (taRecord). - LetA be ?
TypedArrayCreateSameType (O, «𝔽 (length) »). - Letk be 0.
- Repeat, whilek <length,
- ReturnA.
23.2.3.33 %TypedArray%.prototype.toSorted (comparefn )
This method performs the following steps when called:
- Ifcomparefn is not
undefined andIsCallable (comparefn) isfalse , throw aTypeError exception. - LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetA be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - NOTE: The following closure performs a numeric comparison rather than the string comparison used in
23.1.3.34 . - LetSortCompare be a new
Abstract Closure with parameters (x,y) that capturescomparefn and performs the following steps when called:- Return ?
CompareTypedArrayElements (x,y,comparefn).
- Return ?
- LetsortedList be ?
SortIndexedProperties (O,len,SortCompare,read-through-holes ). - Letj be 0.
- Repeat, whilej <len,
- ReturnA.
23.2.3.34 %TypedArray%.prototype.toString ( )
The initial value of the
23.2.3.35 %TypedArray%.prototype.values ( )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
ValidateTypedArray (O,seq-cst ). - Return
CreateArrayIterator (O,value ).
23.2.3.36 %TypedArray%.prototype.with (index,value )
This method performs the following steps when called:
- LetO be the
this value. - LettaRecord be ?
ValidateTypedArray (O,seq-cst ). - Letlen be
TypedArrayLength (taRecord). - LetrelativeIndex be ?
ToIntegerOrInfinity (index). - IfrelativeIndex ≥ 0, letactualIndex berelativeIndex.
- Else, letactualIndex belen +relativeIndex.
- IfO.[[ContentType]] is
bigint , letnumericValue be ?ToBigInt (value). - Else, letnumericValue be ?
ToNumber (value). - If
IsValidIntegerIndex (O,𝔽 (actualIndex)) isfalse , throw aRangeError exception. - LetA be ?
TypedArrayCreateSameType (O, «𝔽 (len) »). - Letk be 0.
- Repeat, whilek <len,
- ReturnA.
23.2.3.37 %TypedArray%.prototype [ @@iterator ] ( )
The initial value of the
23.2.3.38 get %TypedArray%.prototype [ @@toStringTag ]
.prototype[@@toStringTag] is an
- LetO be the
this value. - IfO
is not an Object , returnundefined . - IfO does not have a[[TypedArrayName]] internal slot, return
undefined . - Letname beO.[[TypedArrayName]].
Assert :nameis a String .- Returnname.
This property has the attributes {[[Enumerable]]:
The initial value of the
23.2.4 Abstract Operations for TypedArray Objects
23.2.4.1 TypedArraySpeciesCreate (exemplar,argumentList )
The abstract operation TypedArraySpeciesCreate takes argumentsexemplar (a
- LetdefaultConstructor be the intrinsic object associated with the
constructor nameexemplar.[[TypedArrayName]] inTable 71 . - Letconstructor be ?
SpeciesConstructor (exemplar,defaultConstructor). - Letresult be ?
TypedArrayCreateFromConstructor (constructor,argumentList). Assert :result has[[TypedArrayName]] and[[ContentType]] internal slots.- Ifresult.[[ContentType]] is notexemplar.[[ContentType]], throw a
TypeError exception. - Returnresult.
23.2.4.2 TypedArrayCreateFromConstructor (constructor,argumentList )
The abstract operation TypedArrayCreateFromConstructor takes argumentsconstructor (a
- LetnewTypedArray be ?
Construct (constructor,argumentList). - LettaRecord be ?
ValidateTypedArray (newTypedArray,seq-cst ). - If the number of elements inargumentList is 1 andargumentList[0]
is a Number , then- If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - Letlength be
TypedArrayLength (taRecord). - Iflength <
ℝ (argumentList[0]), throw aTypeError exception.
- If
- ReturnnewTypedArray.
23.2.4.3 TypedArrayCreateSameType (exemplar,argumentList )
The abstract operation TypedArrayCreateSameType takes argumentsexemplar (a
- Letconstructor be the intrinsic object associated with the
constructor nameexemplar.[[TypedArrayName]] inTable 71 . - Letresult be ?
TypedArrayCreateFromConstructor (constructor,argumentList). Assert :result has[[TypedArrayName]] and[[ContentType]] internal slots.Assert :result.[[ContentType]] isexemplar.[[ContentType]].- Returnresult.
23.2.4.4 ValidateTypedArray (O,order )
The abstract operation ValidateTypedArray takes argumentsO (an
- Perform ?
RequireInternalSlot (O,[[TypedArrayName]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (O,order). - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. - ReturntaRecord.
23.2.4.5 TypedArrayElementSize (O )
The abstract operation TypedArrayElementSize takes argumentO (a
- Return the Element Size value specified in
Table 71 forO.[[TypedArrayName]].
23.2.4.6 TypedArrayElementType (O )
The abstract operation TypedArrayElementType takes argumentO (a
- Return the Element Type value specified in
Table 71 forO.[[TypedArrayName]].
23.2.4.7 CompareTypedArrayElements (x,y,comparefn )
The abstract operation CompareTypedArrayElements takes argumentsx (a Number or a BigInt),y (a Number or a BigInt), andcomparefn (a
Assert :xis a Number andyis a Number , orxis a BigInt andyis a BigInt .- Ifcomparefn is not
undefined , then - Ifx andy are both
NaN , return+0 𝔽. - Ifx is
NaN , return1 𝔽. - Ify is
NaN , return-1 𝔽. - Ifx <y, return
-1 𝔽. - Ifx >y, return
1 𝔽. - Ifx is
-0 𝔽 andy is+0 𝔽, return-1 𝔽. - Ifx is
+0 𝔽 andy is-0 𝔽, return1 𝔽. - Return
+0 𝔽.
23.2.5 TheTypedArray Constructors
EachTypedArray
- is an intrinsic object that has the structure described below, differing only in the name used as the
constructor name instead ofTypedArray, inTable 71 . - is a function whose behaviour differs based upon the number and types of its arguments. The actual behaviour of a call ofTypedArray depends upon the number and kind of arguments that are passed to it.
- is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedTypedArray behaviour must include asupercall to theTypedArrayconstructor to create and initialize the subclass instance with the internal state necessary to support the%TypedArray% .prototypebuilt-in methods.
23.2.5.1TypedArray ( ...args )
EachTypedArray
- If NewTarget is
undefined , throw aTypeError exception. - LetconstructorName be the String value of the
Constructor Name value specified inTable 71 for thisTypedArrayconstructor . - Letproto be
"%TypedArray.prototype%". - LetnumberOfArgs be the number of elements inargs.
- IfnumberOfArgs = 0, then
- Return ?
AllocateTypedArray (constructorName, NewTarget,proto, 0).
- Return ?
- Else,
- LetfirstArgument beargs[0].
- IffirstArgument
is an Object , then- LetO be ?
AllocateTypedArray (constructorName, NewTarget,proto). - IffirstArgument has a[[TypedArrayName]] internal slot, then
- Perform ?
InitializeTypedArrayFromTypedArray (O,firstArgument).
- Perform ?
- Else iffirstArgument has an[[ArrayBufferData]] internal slot, then
- IfnumberOfArgs > 1, letbyteOffset beargs[1]; else letbyteOffset be
undefined . - IfnumberOfArgs > 2, letlength beargs[2]; else letlength be
undefined . - Perform ?
InitializeTypedArrayFromArrayBuffer (O,firstArgument,byteOffset,length).
- IfnumberOfArgs > 1, letbyteOffset beargs[1]; else letbyteOffset be
- Else,
Assert :firstArgumentis an Object andfirstArgument does not have either a[[TypedArrayName]] or an[[ArrayBufferData]] internal slot.- LetusingIterator be ?
GetMethod (firstArgument,@@iterator ). - IfusingIterator is not
undefined , then- Letvalues be ?
IteratorToList (?GetIteratorFromMethod (firstArgument,usingIterator)). - Perform ?
InitializeTypedArrayFromList (O,values).
- Letvalues be ?
- Else,
- NOTE:firstArgument is not an Iterable so assume it is already an
array-like object . - Perform ?
InitializeTypedArrayFromArrayLike (O,firstArgument).
- NOTE:firstArgument is not an Iterable so assume it is already an
- ReturnO.
- LetO be ?
- Else,
Assert :firstArgumentis not an Object .- LetelementLength be ?
ToIndex (firstArgument). - Return ?
AllocateTypedArray (constructorName, NewTarget,proto,elementLength).
23.2.5.1.1 AllocateTypedArray (constructorName,newTarget,defaultProto [ ,length ] )
The abstract operation AllocateTypedArray takes argumentsconstructorName (a String which is the name of a
- Letproto be ?
GetPrototypeFromConstructor (newTarget,defaultProto). - Letobj be
TypedArrayCreate (proto). Assert :obj.[[ViewedArrayBuffer]] isundefined .- Setobj.[[TypedArrayName]] toconstructorName.
- IfconstructorName is either
"BigInt64Array" or"BigUint64Array" , setobj.[[ContentType]] tobigint . - Otherwise, setobj.[[ContentType]] to
number . - Iflength is not present, then
- Setobj.[[ByteLength]] to 0.
- Setobj.[[ByteOffset]] to 0.
- Setobj.[[ArrayLength]] to 0.
- Else,
- Perform ?
AllocateTypedArrayBuffer (obj,length).
- Perform ?
- Returnobj.
23.2.5.1.2 InitializeTypedArrayFromTypedArray (O,srcArray )
The abstract operation InitializeTypedArrayFromTypedArray takes argumentsO (a
- LetsrcData besrcArray.[[ViewedArrayBuffer]].
- LetelementType be
TypedArrayElementType (O). - LetelementSize be
TypedArrayElementSize (O). - LetsrcType be
TypedArrayElementType (srcArray). - LetsrcElementSize be
TypedArrayElementSize (srcArray). - LetsrcByteOffset besrcArray.[[ByteOffset]].
- LetsrcRecord be
MakeTypedArrayWithBufferWitnessRecord (srcArray,seq-cst ). - If
IsTypedArrayOutOfBounds (srcRecord) istrue , throw aTypeError exception. - LetelementLength be
TypedArrayLength (srcRecord). - LetbyteLength beelementSize ×elementLength.
- IfelementType issrcType, then
- Letdata be ?
CloneArrayBuffer (srcData,srcByteOffset,byteLength).
- Letdata be ?
- Else,
- Letdata be ?
AllocateArrayBuffer (%ArrayBuffer% ,byteLength). - IfsrcArray.[[ContentType]] is notO.[[ContentType]], throw a
TypeError exception. - LetsrcByteIndex besrcByteOffset.
- LettargetByteIndex be 0.
- Letcount beelementLength.
- Repeat, whilecount > 0,
- Letvalue be
GetValueFromBuffer (srcData,srcByteIndex,srcType,true ,unordered ). - Perform
SetValueInBuffer (data,targetByteIndex,elementType,value,true ,unordered ). - SetsrcByteIndex tosrcByteIndex +srcElementSize.
- SettargetByteIndex totargetByteIndex +elementSize.
- Setcount tocount - 1.
- Letvalue be
- Letdata be ?
- SetO.[[ViewedArrayBuffer]] todata.
- SetO.[[ByteLength]] tobyteLength.
- SetO.[[ByteOffset]] to 0.
- SetO.[[ArrayLength]] toelementLength.
- Return
unused .
23.2.5.1.3 InitializeTypedArrayFromArrayBuffer (O,buffer,byteOffset,length )
The abstract operation InitializeTypedArrayFromArrayBuffer takes argumentsO (a
- LetelementSize be
TypedArrayElementSize (O). - Letoffset be ?
ToIndex (byteOffset). - Ifoffset
modulo elementSize ≠ 0, throw aRangeError exception. - LetbufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - Iflength is not
undefined , then- LetnewLength be ?
ToIndex (length).
- LetnewLength be ?
- If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - LetbufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - Iflength is
undefined andbufferIsFixedLength isfalse , then- Ifoffset >bufferByteLength, throw a
RangeError exception. - SetO.[[ByteLength]] to
auto . - SetO.[[ArrayLength]] to
auto .
- Ifoffset >bufferByteLength, throw a
- Else,
- Iflength is
undefined , then- IfbufferByteLength
modulo elementSize ≠ 0, throw aRangeError exception. - LetnewByteLength bebufferByteLength -offset.
- IfnewByteLength < 0, throw a
RangeError exception.
- IfbufferByteLength
- Else,
- LetnewByteLength benewLength ×elementSize.
- Ifoffset +newByteLength >bufferByteLength, throw a
RangeError exception.
- SetO.[[ByteLength]] tonewByteLength.
- SetO.[[ArrayLength]] tonewByteLength /elementSize.
- Iflength is
- SetO.[[ViewedArrayBuffer]] tobuffer.
- SetO.[[ByteOffset]] tooffset.
- Return
unused .
23.2.5.1.4 InitializeTypedArrayFromList (O,values )
The abstract operation InitializeTypedArrayFromList takes argumentsO (a
- Letlen be the number of elements invalues.
- Perform ?
AllocateTypedArrayBuffer (O,len). - Letk be 0.
- Repeat, whilek <len,
Assert :values is now an emptyList .- Return
unused .
23.2.5.1.5 InitializeTypedArrayFromArrayLike (O,arrayLike )
The abstract operation InitializeTypedArrayFromArrayLike takes argumentsO (a
- Letlen be ?
LengthOfArrayLike (arrayLike). - Perform ?
AllocateTypedArrayBuffer (O,len). - Letk be 0.
- Repeat, whilek <len,
- Return
unused .
23.2.5.1.6 AllocateTypedArrayBuffer (O,length )
The abstract operation AllocateTypedArrayBuffer takes argumentsO (a
Assert :O.[[ViewedArrayBuffer]] isundefined .- LetelementSize be
TypedArrayElementSize (O). - LetbyteLength beelementSize ×length.
- Letdata be ?
AllocateArrayBuffer (%ArrayBuffer% ,byteLength). - SetO.[[ViewedArrayBuffer]] todata.
- SetO.[[ByteLength]] tobyteLength.
- SetO.[[ByteOffset]] to 0.
- SetO.[[ArrayLength]] tolength.
- Return
unused .
23.2.6 Properties of theTypedArray Constructors
EachTypedArray
- has a[[Prototype]] internal slot whose value is
%TypedArray% . - has a
"length" property whose value is3 𝔽. - has a
"name" property whose value is the String value of theconstructor name specified for it inTable 71 . - has the following properties:
23.2.6.1TypedArray.BYTES_PER_ELEMENT
The value ofTypedArray.BYTES_PER_ELEMENT is the Element Size value specified in
This property has the attributes {[[Writable]]:
23.2.6.2TypedArray.prototype
The initial value ofTypedArray.prototype is the correspondingTypedArray prototype intrinsic object (
This property has the attributes {[[Writable]]:
23.2.7 Properties of theTypedArray Prototype Objects
EachTypedArray prototype object:
- has a[[Prototype]] internal slot whose value is
%TypedArray.prototype% . - is an
ordinary object . - does not have a[[ViewedArrayBuffer]] or any other of the internal slots that are specific toTypedArray instance objects.
23.2.7.1TypedArray.prototype.BYTES_PER_ELEMENT
The value ofTypedArray.prototype.BYTES_PER_ELEMENT is the Element Size value specified in
This property has the attributes {[[Writable]]:
23.2.7.2TypedArray.prototype.constructor
The initial value of the
23.2.8 Properties ofTypedArray Instances
TypedArray instances are
24 Keyed Collections
24.1 Map Objects
Maps are collections of key/value pairs where both the keys and values may be arbitrary
Maps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Maps. It is not intended to be a viable implementation model.
24.1.1 The Map Constructor
The Map
- is%Map%.
- is the initial value of the
"Map" property of theglobal object . - creates and initializes a new Map when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Map behaviour must include asupercall to the Mapconstructor to create and initialize the subclass instance with the internal state necessary to support theMap.prototypebuilt-in methods.
24.1.1.1 Map ( [iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Letmap be ?
OrdinaryCreateFromConstructor (NewTarget,"%Map.prototype%" , «[[MapData]] »). - Setmap.[[MapData]] to a new empty
List . - Ifiterable is either
undefined ornull , returnmap. - Letadder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map,iterable,adder).
If the parameteriterable is present, it is expected to be an object that implements an
24.1.1.2 AddEntriesFromIterable (target,iterable,adder )
The abstract operation AddEntriesFromIterable takes argumentstarget (an Object),iterable (an
- LetiteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returntarget. - Ifnext
is not an Object , then- Leterror be
ThrowCompletion (a newly createdTypeError object). - Return ?
IteratorClose (iteratorRecord,error).
- Leterror be
- Letk be
Completion (Get (next,"0" )). IfAbruptCloseIterator (k,iteratorRecord).- Letv be
Completion (Get (next,"1" )). IfAbruptCloseIterator (v,iteratorRecord).- Letstatus be
Completion (Call (adder,target, «k,v »)). IfAbruptCloseIterator (status,iteratorRecord).
- Letnext be ?
The parameteriterable is expected to be an object that implements an
24.1.2 Properties of the Map Constructor
The Map
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.1.2.1 Map.groupBy (items,callbackfn )
callbackfn should be a function that accepts two arguments.groupBy callscallbackfn once for each element initems, in ascending order, and constructs a new Map. Each value returned bycallbackfn is used as a key in the Map. For each such key, the result Map has an entry whose key is that key and whose value is an array containing all the elements for whichcallbackfn returned that key.
callbackfn is called with two arguments: the value of the element and the index of the element.
The return value ofgroupBy is a Map.
This function performs the following steps when called:
24.1.2.2 Map.prototype
The initial value ofMap.prototype is the
This property has the attributes {[[Writable]]:
24.1.2.3 get Map [ @@species ]
Map[@@species] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.1.3 Properties of the Map Prototype Object
TheMap prototype object:
- is%Map.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[MapData]] internal slot.
24.1.3.1 Map.prototype.clear ( )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Setp.[[Key]] to
empty . - Setp.[[Value]] to
empty .
- Setp.[[Key]] to
- Return
undefined .
24.1.3.2 Map.prototype.constructor
The initial value ofMap.prototype.constructor is
24.1.3.3 Map.prototype.delete (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Ifp.[[Key]] is not
empty andSameValueZero (p.[[Key]],key) istrue , then- Setp.[[Key]] to
empty . - Setp.[[Value]] to
empty . - Return
true .
- Setp.[[Key]] to
- Ifp.[[Key]] is not
- Return
false .
The value
24.1.3.4 Map.prototype.entries ( )
This method performs the following steps when called:
- LetM be the
this value. - Return ?
CreateMapIterator (M,key+value ).
24.1.3.5 Map.prototype.forEach (callbackfn [ ,thisArg ] )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letentries beM.[[MapData]].
- LetnumEntries be the number of elements inentries.
- Letindex be 0.
- Repeat, whileindex <numEntries,
- Lete beentries[index].
- Setindex toindex + 1.
- Ife.[[Key]] is not
empty , then- Perform ?
Call (callbackfn,thisArg, «e.[[Value]],e.[[Key]],M »). - NOTE: The number of elements inentries may have increased during execution ofcallbackfn.
- SetnumEntries to the number of elements inentries.
- Perform ?
- Return
undefined .
callbackfn should be a function that accepts three arguments.forEach callscallbackfn once for each key/value pair present in the Map, in key insertion order.callbackfn is called only for keys of the Map which actually exist; it is not called for keys that have been deleted from the Map.
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the value of the item, the key of the item, and the Map being traversed.
forEach does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn. Each entry of a map's[[MapData]] is only visited once. New keys added after the call toforEach begins are visited. A key will be revisited if it is deleted after it has been visited and then re-added before theforEach call completes. Keys that are deleted after the call toforEach begins and before being visited are not visited unless the key is added again before theforEach call completes.
24.1.3.6 Map.prototype.get (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Ifp.[[Key]] is not
empty andSameValueZero (p.[[Key]],key) istrue , returnp.[[Value]].
- Ifp.[[Key]] is not
- Return
undefined .
24.1.3.7 Map.prototype.has (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Ifp.[[Key]] is not
empty andSameValueZero (p.[[Key]],key) istrue , returntrue .
- Ifp.[[Key]] is not
- Return
false .
24.1.3.8 Map.prototype.keys ( )
This method performs the following steps when called:
- LetM be the
this value. - Return ?
CreateMapIterator (M,key ).
24.1.3.9 Map.prototype.set (key,value )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Ifp.[[Key]] is not
empty andSameValueZero (p.[[Key]],key) istrue , then- Setp.[[Value]] tovalue.
- ReturnM.
- Ifp.[[Key]] is not
- Ifkey is
-0 𝔽, setkey to+0 𝔽. - Letp be the
Record {[[Key]]:key,[[Value]]:value }. - Appendp toM.[[MapData]].
- ReturnM.
24.1.3.10 get Map.prototype.size
Map.prototype.size is an
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[MapData]]). - Letcount be 0.
- For each
Record {[[Key]],[[Value]] }p ofM.[[MapData]], do- Ifp.[[Key]] is not
empty , setcount tocount + 1.
- Ifp.[[Key]] is not
- Return
𝔽 (count).
24.1.3.11 Map.prototype.values ( )
This method performs the following steps when called:
- LetM be the
this value. - Return ?
CreateMapIterator (M,value ).
24.1.3.12 Map.prototype [ @@iterator ] ( )
The initial value of the
24.1.3.13 Map.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.1.4 Properties of Map Instances
Map instances are
24.1.5 Map Iterator Objects
A Map Iterator is an object, that represents a specific iteration over some specific Map instance object. There is not a named
24.1.5.1 CreateMapIterator (map,kind )
The abstract operation CreateMapIterator takes argumentsmap (an
- Perform ?
RequireInternalSlot (map,[[MapData]]). - Letclosure be a new
Abstract Closure with no parameters that capturesmap andkind and performs the following steps when called:- Letentries bemap.[[MapData]].
- Letindex be 0.
- LetnumEntries be the number of elements inentries.
- Repeat, whileindex <numEntries,
- Lete beentries[index].
- Setindex toindex + 1.
- Ife.[[Key]] is not
empty , then- Ifkind is
key , then- Letresult bee.[[Key]].
- Else ifkind is
value , then- Letresult bee.[[Value]].
- Else,
Assert :kind iskey+value .- Letresult be
CreateArrayFromList («e.[[Key]],e.[[Value]] »).
- Perform ?
GeneratorYield (CreateIterResultObject (result,false )). - NOTE: The number of elements inentries may have increased while execution of this abstract operation was paused by
Yield . - SetnumEntries to the number of elements inentries.
- Ifkind is
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%MapIteratorPrototype%" ,%MapIteratorPrototype% ).
24.1.5.2 The %MapIteratorPrototype% Object
The%MapIteratorPrototype% object:
- has properties that are inherited by all Map Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
24.1.5.2.1 %MapIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%MapIteratorPrototype%" ).
24.1.5.2.2 %MapIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.2 Set Objects
Set objects are collections of
Set objects must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of Set objects. It is not intended to be a viable implementation model.
24.2.1 The Set Constructor
The Set
- is%Set%.
- is the initial value of the
"Set" property of theglobal object . - creates and initializes a new Set object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Set behaviour must include asupercall to the Setconstructor to create and initialize the subclass instance with the internal state necessary to support theSet.prototypebuilt-in methods.
24.2.1.1 Set ( [iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Letset be ?
OrdinaryCreateFromConstructor (NewTarget,"%Set.prototype%" , «[[SetData]] »). - Setset.[[SetData]] to a new empty
List . - Ifiterable is either
undefined ornull , returnset. - Letadder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - LetiteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returnset. - Letstatus be
Completion (Call (adder,set, «next »)). IfAbruptCloseIterator (status,iteratorRecord).
- Letnext be ?
24.2.2 Properties of the Set Constructor
The Set
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.2.2.1 Set.prototype
The initial value ofSet.prototype is the
This property has the attributes {[[Writable]]:
24.2.2.2 get Set [ @@species ]
Set[@@species] is an
- Return the
this value.
The value of the
Methods that create derived collection objects should call
24.2.3 Properties of the Set Prototype Object
TheSet prototype object:
- is%Set.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[SetData]] internal slot.
24.2.3.1 Set.prototype.add (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - For each elemente ofS.[[SetData]], do
- Ife is not
empty andSameValueZero (e,value) istrue , then- ReturnS.
- Ife is not
- Ifvalue is
-0 𝔽, setvalue to+0 𝔽. - Appendvalue toS.[[SetData]].
- ReturnS.
24.2.3.2 Set.prototype.clear ( )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - For each elemente ofS.[[SetData]], do
- Replace the element ofS.[[SetData]] whose value ise with an element whose value is
empty .
- Replace the element ofS.[[SetData]] whose value ise with an element whose value is
- Return
undefined .
24.2.3.3 Set.prototype.constructor
The initial value ofSet.prototype.constructor is
24.2.3.4 Set.prototype.delete (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - For each elemente ofS.[[SetData]], do
- Ife is not
empty andSameValueZero (e,value) istrue , then- Replace the element ofS.[[SetData]] whose value ise with an element whose value is
empty . - Return
true .
- Replace the element ofS.[[SetData]] whose value ise with an element whose value is
- Ife is not
- Return
false .
The value
24.2.3.5 Set.prototype.entries ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateSetIterator (S,key+value ).
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.3.6 Set.prototype.forEach (callbackfn [ ,thisArg ] )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - If
IsCallable (callbackfn) isfalse , throw aTypeError exception. - Letentries beS.[[SetData]].
- LetnumEntries be the number of elements inentries.
- Letindex be 0.
- Repeat, whileindex <numEntries,
- Lete beentries[index].
- Setindex toindex + 1.
- Ife is not
empty , then- Perform ?
Call (callbackfn,thisArg, «e,e,S »). - NOTE: The number of elements inentries may have increased during execution ofcallbackfn.
- SetnumEntries to the number of elements inentries.
- Perform ?
- Return
undefined .
callbackfn should be a function that accepts three arguments.forEach callscallbackfn once for each value present in the Set object, in value insertion order.callbackfn is called only for values of the Set which actually exist; it is not called for keys that have been deleted from the set.
If athisArg parameter is provided, it will be used as the
callbackfn is called with three arguments: the first two arguments are a value contained in the Set. The same value is passed for both arguments. The Set object being traversed is passed as the third argument.
Thecallbackfn is called with three arguments to be consistent with the call back functions used byforEach methods for Map and Array. For Sets, each item value is considered to be both the key and the value.
forEach does not directly mutate the object on which it is called but the object may be mutated by the calls tocallbackfn.
Each value is normally visited only once. However, a value will be revisited if it is deleted after it has been visited and then re-added before theforEach call completes. Values that are deleted after the call toforEach begins and before being visited are not visited unless the value is added again before theforEach call completes. New values added after the call toforEach begins are visited.
24.2.3.7 Set.prototype.has (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - For each elemente ofS.[[SetData]], do
- Ife is not
empty andSameValueZero (e,value) istrue , returntrue .
- Ife is not
- Return
false .
24.2.3.8 Set.prototype.keys ( )
The initial value of the
For iteration purposes, a Set appears similar to a Map where each entry has the same value for its key and value.
24.2.3.9 get Set.prototype.size
Set.prototype.size is an
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[SetData]]). - Letcount be 0.
- For each elemente ofS.[[SetData]], do
- Ife is not
empty , setcount tocount + 1.
- Ife is not
- Return
𝔽 (count).
24.2.3.10 Set.prototype.values ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateSetIterator (S,value ).
24.2.3.11 Set.prototype [ @@iterator ] ( )
The initial value of the
24.2.3.12 Set.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.2.4 Properties of Set Instances
Set instances are
24.2.5 Set Iterator Objects
A Set Iterator is an
24.2.5.1 CreateSetIterator (set,kind )
The abstract operation CreateSetIterator takes argumentsset (an
- Perform ?
RequireInternalSlot (set,[[SetData]]). - Letclosure be a new
Abstract Closure with no parameters that capturesset andkind and performs the following steps when called:- Letindex be 0.
- Letentries beset.[[SetData]].
- LetnumEntries be the number of elements inentries.
- Repeat, whileindex <numEntries,
- Lete beentries[index].
- Setindex toindex + 1.
- Ife is not
empty , then- Ifkind is
key+value , then- Letresult be
CreateArrayFromList («e,e »). - Perform ?
GeneratorYield (CreateIterResultObject (result,false )).
- Letresult be
- Else,
Assert :kind isvalue .- Perform ?
GeneratorYield (CreateIterResultObject (e,false )).
- NOTE: The number of elements inentries may have increased while execution of this abstract operation was paused by
Yield . - SetnumEntries to the number of elements inentries.
- Ifkind is
- Return
undefined .
- Return
CreateIteratorFromClosure (closure,"%SetIteratorPrototype%" ,%SetIteratorPrototype% ).
24.2.5.2 The %SetIteratorPrototype% Object
The%SetIteratorPrototype% object:
- has properties that are inherited by all Set Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has the following properties:
24.2.5.2.1 %SetIteratorPrototype%.next ( )
- Return ?
GeneratorResume (this value,empty ,"%SetIteratorPrototype%" ).
24.2.5.2.2 %SetIteratorPrototype% [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.3 WeakMap Objects
WeakMaps are collections of key/value pairs where the keys are objects and/or symbols and values may be arbitrary
An implementation may impose an arbitrarily determined latency between the time a key/value pair of a WeakMap becomes inaccessible and the time when the key/value pair is removed from the WeakMap. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to observe a key of a WeakMap that does not require the observer to present the observed key.
WeakMaps must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of key/value pairs in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakMaps. It is not intended to be a viable implementation model.
WeakMap and WeakSet are intended to provide mechanisms for dynamically associating state with an object or symbol in a manner that does not “leak” memory resources if, in the absence of the WeakMap or WeakSet instance, the object or symbol otherwise became inaccessible and subject to resource reclamation by the implementation's garbage collection mechanisms. This characteristic can be achieved by using an inverted per-object/symbol mapping of WeakMap or WeakSet instances to keys. Alternatively, each WeakMap or WeakSet instance may internally store its key and value data, but this approach requires coordination between the WeakMap or WeakSet implementation and the garbage collector. The following references describe mechanism that may be useful to implementations of WeakMap and WeakSet:
Barry Hayes. 1997. Ephemerons: a new finalization mechanism. InProceedings of the 12th ACM SIGPLAN conference on Object-oriented programming, systems, languages, and applications (OOPSLA '97), A. Michael Berman (Ed.). ACM, New York, NY, USA, 176-183,http://doi.acm.org/10.1145/263698.263733.
Alexandra Barros, Roberto Ierusalimschy, Eliminating Cycles in Weak Tables. Journal of Universal Computer Science - J.UCS, vol. 14, no. 21, pp. 3481-3497, 2008,http://www.jucs.org/jucs_14_21/eliminating_cycles_in_weak
24.3.1 The WeakMap Constructor
The WeakMap
- is%WeakMap%.
- is the initial value of the
"WeakMap" property of theglobal object . - creates and initializes a new WeakMap when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakMap behaviour must include asupercall to the WeakMapconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakMap.prototypebuilt-in methods.
24.3.1.1 WeakMap ( [iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Letmap be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakMap.prototype%" , «[[WeakMapData]] »). - Setmap.[[WeakMapData]] to a new empty
List . - Ifiterable is either
undefined ornull , returnmap. - Letadder be ?
Get (map,"set" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - Return ?
AddEntriesFromIterable (map,iterable,adder).
If the parameteriterable is present, it is expected to be an object that implements an
24.3.2 Properties of the WeakMap Constructor
The WeakMap
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.3.2.1 WeakMap.prototype
The initial value ofWeakMap.prototype is the
This property has the attributes {[[Writable]]:
24.3.3 Properties of the WeakMap Prototype Object
TheWeakMap prototype object:
- is%WeakMap.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[WeakMapData]] internal slot.
24.3.3.1 WeakMap.prototype.constructor
The initial value ofWeakMap.prototype.constructor is
24.3.3.2 WeakMap.prototype.delete (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record {[[Key]],[[Value]] }p ofM.[[WeakMapData]], do- Ifp.[[Key]] is not
empty andSameValue (p.[[Key]],key) istrue , then- Setp.[[Key]] to
empty . - Setp.[[Value]] to
empty . - Return
true .
- Setp.[[Key]] to
- Ifp.[[Key]] is not
- Return
false .
The value
24.3.3.3 WeakMap.prototype.get (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnundefined . - For each
Record {[[Key]],[[Value]] }p ofM.[[WeakMapData]], do- Ifp.[[Key]] is not
empty andSameValue (p.[[Key]],key) istrue , returnp.[[Value]].
- Ifp.[[Key]] is not
- Return
undefined .
24.3.3.4 WeakMap.prototype.has (key )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , returnfalse . - For each
Record {[[Key]],[[Value]] }p ofM.[[WeakMapData]], do- Ifp.[[Key]] is not
empty andSameValue (p.[[Key]],key) istrue , returntrue .
- Ifp.[[Key]] is not
- Return
false .
24.3.3.5 WeakMap.prototype.set (key,value )
This method performs the following steps when called:
- LetM be the
this value. - Perform ?
RequireInternalSlot (M,[[WeakMapData]]). - If
CanBeHeldWeakly (key) isfalse , throw aTypeError exception. - For each
Record {[[Key]],[[Value]] }p ofM.[[WeakMapData]], do- Ifp.[[Key]] is not
empty andSameValue (p.[[Key]],key) istrue , then- Setp.[[Value]] tovalue.
- ReturnM.
- Ifp.[[Key]] is not
- Letp be the
Record {[[Key]]:key,[[Value]]:value }. - Appendp toM.[[WeakMapData]].
- ReturnM.
24.3.3.6 WeakMap.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.3.4 Properties of WeakMap Instances
WeakMap instances are
24.4 WeakSet Objects
WeakSets are collections of objects and/or symbols. A distinct object or symbol may only occur once as an element of a WeakSet's collection. A WeakSet may be queried to see if it contains a specific value, but no mechanism is provided for enumerating the values it holds. In certain conditions, values which are not
An implementation may impose an arbitrarily determined latency between the time a value contained in a WeakSet becomes inaccessible and the time when the value is removed from the WeakSet. If this latency was observable to ECMAScript program, it would be a source of indeterminacy that could impact program execution. For that reason, an ECMAScript implementation must not provide any means to determine if a WeakSet contains a particular value that does not require the observer to present the observed value.
WeakSets must be implemented using either hash tables or other mechanisms that, on average, provide access times that are sublinear on the number of elements in the collection. The data structure used in this specification is only intended to describe the required observable semantics of WeakSets. It is not intended to be a viable implementation model.
See the NOTE in
24.4.1 The WeakSet Constructor
The WeakSet
- is%WeakSet%.
- is the initial value of the
"WeakSet" property of theglobal object . - creates and initializes a new WeakSet when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified WeakSet behaviour must include asupercall to the WeakSetconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakSet.prototypebuilt-in methods.
24.4.1.1 WeakSet ( [iterable ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Letset be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakSet.prototype%" , «[[WeakSetData]] »). - Setset.[[WeakSetData]] to a new empty
List . - Ifiterable is either
undefined ornull , returnset. - Letadder be ?
Get (set,"add" ). - If
IsCallable (adder) isfalse , throw aTypeError exception. - LetiteratorRecord be ?
GetIterator (iterable,sync ). - Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , returnset. - Letstatus be
Completion (Call (adder,set, «next »)). IfAbruptCloseIterator (status,iteratorRecord).
- Letnext be ?
24.4.2 Properties of the WeakSet Constructor
The WeakSet
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
24.4.2.1 WeakSet.prototype
The initial value ofWeakSet.prototype is the
This property has the attributes {[[Writable]]:
24.4.3 Properties of the WeakSet Prototype Object
TheWeakSet prototype object:
- is%WeakSet.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[WeakSetData]] internal slot.
24.4.3.1 WeakSet.prototype.add (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , throw aTypeError exception. - For each elemente ofS.[[WeakSetData]], do
- Ife is not
empty andSameValue (e,value) istrue , then- ReturnS.
- Ife is not
- Appendvalue toS.[[WeakSetData]].
- ReturnS.
24.4.3.2 WeakSet.prototype.constructor
The initial value ofWeakSet.prototype.constructor is
24.4.3.3 WeakSet.prototype.delete (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each elemente ofS.[[WeakSetData]], do
- Ife is not
empty andSameValue (e,value) istrue , then- Replace the element ofS.[[WeakSetData]] whose value ise with an element whose value is
empty . - Return
true .
- Replace the element ofS.[[WeakSetData]] whose value ise with an element whose value is
- Ife is not
- Return
false .
The value
24.4.3.4 WeakSet.prototype.has (value )
This method performs the following steps when called:
- LetS be the
this value. - Perform ?
RequireInternalSlot (S,[[WeakSetData]]). - If
CanBeHeldWeakly (value) isfalse , returnfalse . - For each elemente ofS.[[WeakSetData]], do
- Ife is not
empty andSameValue (e,value) istrue , returntrue .
- Ife is not
- Return
false .
24.4.3.5 WeakSet.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
24.4.4 Properties of WeakSet Instances
WeakSet instances are
25 Structured Data
25.1 ArrayBuffer Objects
25.1.1 Notation
The descriptions below in this section,
Aread-modify-write modification function is a mathematical function that is notationally represented as an abstract closure that takes two
- They perform all their algorithm steps atomically.
- Their individual algorithm steps are not observable.
To aid verifying that a read-modify-write modification function's algorithm steps constitute a pure, mathematical function, the following editorial conventions are recommended:
- They do not access, directly or transitively via invoked
abstract operations and abstract closures, any language or specification values except their parameters and captured values. - They do not return
Completion Records .
25.1.2 Fixed-length and Resizable ArrayBuffer Objects
Afixed-length ArrayBuffer is an ArrayBuffer whose byte length cannot change after creation.
Aresizable ArrayBuffer is an ArrayBuffer whose byte length may change after creation via calls to
The kind of ArrayBuffer object that is created depends on the arguments passed to
25.1.3 Abstract Operations For ArrayBuffer Objects
25.1.3.1 AllocateArrayBuffer (constructor,byteLength [ ,maxByteLength ] )
The abstract operation AllocateArrayBuffer takes argumentsconstructor (a
- Letslots be «[[ArrayBufferData]],[[ArrayBufferByteLength]],[[ArrayBufferDetachKey]] ».
- IfmaxByteLength is present andmaxByteLength is not
empty , letallocatingResizableBuffer betrue ; otherwise letallocatingResizableBuffer befalse . - IfallocatingResizableBuffer is
true , then- IfbyteLength >maxByteLength, throw a
RangeError exception. - Append[[ArrayBufferMaxByteLength]] toslots.
- IfbyteLength >maxByteLength, throw a
- Letobj be ?
OrdinaryCreateFromConstructor (constructor,"%ArrayBuffer.prototype%" ,slots). - Letblock be ?
CreateByteDataBlock (byteLength). - Setobj.[[ArrayBufferData]] toblock.
- Setobj.[[ArrayBufferByteLength]] tobyteLength.
- IfallocatingResizableBuffer is
true , then- If it is not possible to create a
Data Block block consisting ofmaxByteLength bytes, throw aRangeError exception. - NOTE: Resizable ArrayBuffers are designed to be implementable with in-place growth. Implementations may throw if, for example, virtual memory cannot be reserved up front.
- Setobj.[[ArrayBufferMaxByteLength]] tomaxByteLength.
- If it is not possible to create a
- Returnobj.
25.1.3.2 ArrayBufferByteLength (arrayBuffer,order )
The abstract operation ArrayBufferByteLength takes argumentsarrayBuffer (an ArrayBuffer or SharedArrayBuffer) andorder (
- If
IsSharedArrayBuffer (arrayBuffer) istrue andarrayBuffer has an[[ArrayBufferByteLengthData]] internal slot, then- LetbufferByteLengthBlock bearrayBuffer.[[ArrayBufferByteLengthData]].
- LetrawLength be
GetRawBytesFromSharedBlock (bufferByteLengthBlock, 0,biguint64 ,true ,order). - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Return
ℝ (RawBytesToNumeric (biguint64 ,rawLength,isLittleEndian)).
Assert :IsDetachedBuffer (arrayBuffer) isfalse .- ReturnarrayBuffer.[[ArrayBufferByteLength]].
25.1.3.3 ArrayBufferCopyAndDetach (arrayBuffer,newLength,preserveResizability )
The abstract operation ArrayBufferCopyAndDetach takes argumentsarrayBuffer (an
- Perform ?
RequireInternalSlot (arrayBuffer,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (arrayBuffer) istrue , throw aTypeError exception. - IfnewLength is
undefined , then- LetnewByteLength bearrayBuffer.[[ArrayBufferByteLength]].
- Else,
- LetnewByteLength be ?
ToIndex (newLength).
- LetnewByteLength be ?
- If
IsDetachedBuffer (arrayBuffer) istrue , throw aTypeError exception. - IfpreserveResizability is
preserve-resizability andIsFixedLengthArrayBuffer (arrayBuffer) isfalse , then- LetnewMaxByteLength bearrayBuffer.[[ArrayBufferMaxByteLength]].
- Else,
- LetnewMaxByteLength be
empty .
- LetnewMaxByteLength be
- IfarrayBuffer.[[ArrayBufferDetachKey]] is not
undefined , throw aTypeError exception. - LetnewBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% ,newByteLength,newMaxByteLength). - LetcopyLength be
min (newByteLength,arrayBuffer.[[ArrayBufferByteLength]]). - LetfromBlock bearrayBuffer.[[ArrayBufferData]].
- LettoBlock benewBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBlock, 0,fromBlock, 0,copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as a zero-copy move or arealloc. - Perform !
DetachArrayBuffer (arrayBuffer). - ReturnnewBuffer.
25.1.3.4 IsDetachedBuffer (arrayBuffer )
The abstract operation IsDetachedBuffer takes argumentarrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- IfarrayBuffer.[[ArrayBufferData]] is
null , returntrue . - Return
false .
25.1.3.5 DetachArrayBuffer (arrayBuffer [ ,key ] )
The abstract operation DetachArrayBuffer takes argumentarrayBuffer (an ArrayBuffer) and optional argumentkey (anything) and returns either a
Assert :IsSharedArrayBuffer (arrayBuffer) isfalse .- Ifkey is not present, setkey to
undefined . - IfarrayBuffer.[[ArrayBufferDetachKey]] is notkey, throw a
TypeError exception. - SetarrayBuffer.[[ArrayBufferData]] to
null . - SetarrayBuffer.[[ArrayBufferByteLength]] to 0.
- Return
unused .
Detaching an ArrayBuffer instance disassociates the
25.1.3.6 CloneArrayBuffer (srcBuffer,srcByteOffset,srcLength )
The abstract operation CloneArrayBuffer takes argumentssrcBuffer (an ArrayBuffer or a SharedArrayBuffer),srcByteOffset (a non-negative
Assert :IsDetachedBuffer (srcBuffer) isfalse .- LettargetBuffer be ?
AllocateArrayBuffer (%ArrayBuffer% ,srcLength). - LetsrcBlock besrcBuffer.[[ArrayBufferData]].
- LettargetBlock betargetBuffer.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (targetBlock, 0,srcBlock,srcByteOffset,srcLength). - ReturntargetBuffer.
25.1.3.7 GetArrayBufferMaxByteLengthOption (options )
The abstract operation GetArrayBufferMaxByteLengthOption takes argumentoptions (an
- Ifoptions
is not an Object , returnempty . - LetmaxByteLength be ?
Get (options,"maxByteLength" ). - IfmaxByteLength is
undefined , returnempty . - Return ?
ToIndex (maxByteLength).
25.1.3.8 HostResizeArrayBuffer (buffer,newByteLength )
The
The implementation of HostResizeArrayBuffer must conform to the following requirements:
- The abstract operation does not detachbuffer.
- If the abstract operation completes normally with
handled ,buffer.[[ArrayBufferByteLength]] isnewByteLength.
The default implementation of HostResizeArrayBuffer is to return
25.1.3.9 IsFixedLengthArrayBuffer (arrayBuffer )
The abstract operation IsFixedLengthArrayBuffer takes argumentarrayBuffer (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It performs the following steps when called:
- IfarrayBuffer has an[[ArrayBufferMaxByteLength]] internal slot, return
false . - Return
true .
25.1.3.10 IsUnsignedElementType (type )
The abstract operation IsUnsignedElementType takes argumenttype (a
- Iftype is one of
uint8 ,uint8clamped ,uint16 ,uint32 , orbiguint64 , returntrue . - Return
false .
25.1.3.11 IsUnclampedIntegerElementType (type )
The abstract operation IsUnclampedIntegerElementType takes argumenttype (a
- Iftype is one of
int8 ,uint8 ,int16 ,uint16 ,int32 , oruint32 , returntrue . - Return
false .
25.1.3.12 IsBigIntElementType (type )
The abstract operation IsBigIntElementType takes argumenttype (a
- Iftype is either
biguint64 orbigint64 , returntrue . - Return
false .
25.1.3.13 IsNoTearConfiguration (type,order )
The abstract operation IsNoTearConfiguration takes argumentstype (a
- If
IsUnclampedIntegerElementType (type) istrue , returntrue . - If
IsBigIntElementType (type) istrue andorder is neitherinit norunordered , returntrue . - Return
false .
25.1.3.14 RawBytesToNumeric (type,rawBytes,isLittleEndian )
The abstract operation RawBytesToNumeric takes argumentstype (a
- LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - IfisLittleEndian is
false , reverse the order of the elements ofrawBytes. - Iftype is
float32 , then- Letvalue be the byte elements ofrawBytes concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary32 value. - Ifvalue is an
IEEE 754-2019 binary32 NaN value, return theNaN Number value. - Return the Number value that corresponds tovalue.
- Letvalue be the byte elements ofrawBytes concatenated and interpreted as a little-endian bit string encoding of an
- Iftype is
float64 , then- Letvalue be the byte elements ofrawBytes concatenated and interpreted as a little-endian bit string encoding of an
IEEE 754-2019 binary64 value. - Ifvalue is an
IEEE 754-2019 binary64 NaN value, return theNaN Number value. - Return the Number value that corresponds tovalue.
- Letvalue be the byte elements ofrawBytes concatenated and interpreted as a little-endian bit string encoding of an
- If
IsUnsignedElementType (type) istrue , then- LetintValue be the byte elements ofrawBytes concatenated and interpreted as a bit string encoding of an unsigned little-endian binary number.
- Else,
- LetintValue be the byte elements ofrawBytes concatenated and interpreted as a bit string encoding of a binary little-endian two's complement number of bit lengthelementSize × 8.
- If
IsBigIntElementType (type) istrue , return the BigInt value that corresponds tointValue. - Otherwise, return the Number value that corresponds tointValue.
25.1.3.15 GetRawBytesFromSharedBlock (block,byteIndex,type,isTypedArray,order )
The abstract operation GetRawBytesFromSharedBlock takes argumentsblock (a
- LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - IfisTypedArray is
true andIsNoTearConfiguration (type,order) istrue , letnoTear betrue ; otherwise letnoTear befalse . - LetrawValue be a
List of lengthelementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations,rawValue is the result of a non-atomic or atomic read instruction on the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - LetreadEvent be
ReadSharedMemory {[[Order]]:order,[[NoTear]]:noTear,[[Block]]:block,[[ByteIndex]]:byteIndex,[[ElementSize]]:elementSize }. - AppendreadEvent toeventsRecord.[[EventList]].
- Append
Chosen Value Record {[[Event]]:readEvent,[[ChosenValue]]:rawValue } toexecution.[[ChosenValues]]. - ReturnrawValue.
25.1.3.16 GetValueFromBuffer (arrayBuffer,byteIndex,type,isTypedArray,order [ ,isLittleEndian ] )
The abstract operation GetValueFromBuffer takes argumentsarrayBuffer (an ArrayBuffer or SharedArrayBuffer),byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes inarrayBuffer starting atbyteIndex to represent a value oftype.- Letblock bearrayBuffer.[[ArrayBufferData]].
- LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - If
IsSharedArrayBuffer (arrayBuffer) istrue , thenAssert :block is aShared Data Block .- LetrawValue be
GetRawBytesFromSharedBlock (block,byteIndex,type,isTypedArray,order).
- Else,
Assert : The number of elements inrawValue iselementSize.- IfisLittleEndian is not present, setisLittleEndian to the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Return
RawBytesToNumeric (type,rawValue,isLittleEndian).
25.1.3.17 NumericToRawBytes (type,value,isLittleEndian )
The abstract operation NumericToRawBytes takes argumentstype (a
- Iftype is
float32 , then- LetrawBytes be a
List whose elements are the 4 bytes that are the result of convertingvalue toIEEE 754-2019 binary32 format using roundTiesToEven mode. The bytes are arranged in little endian order. Ifvalue isNaN ,rawBytes may be set to any implementation chosenIEEE 754-2019 binary32 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- LetrawBytes be a
- Else iftype is
float64 , then- LetrawBytes be a
List whose elements are the 8 bytes that are theIEEE 754-2019 binary64 format encoding ofvalue. The bytes are arranged in little endian order. Ifvalue isNaN ,rawBytes may be set to any implementation chosenIEEE 754-2019 binary64 format Not-a-Number encoding. An implementation must always choose the same encoding for each implementation distinguishableNaN value.
- LetrawBytes be a
- Else,
- Letn be the Element Size value specified in
Table 71 for Element Typetype. - LetconvOp be the abstract operation named in the Conversion Operation column in
Table 71 for Element Typetype. - LetintValue be
ℝ (convOp(value)). - IfintValue ≥ 0, then
- LetrawBytes be a
List whose elements are then-byte binary encoding ofintValue. The bytes are ordered in little endian order.
- LetrawBytes be a
- Else,
- LetrawBytes be a
List whose elements are then-byte binary two's complement encoding ofintValue. The bytes are ordered in little endian order.
- LetrawBytes be a
- Letn be the Element Size value specified in
- IfisLittleEndian is
false , reverse the order of the elements ofrawBytes. - ReturnrawBytes.
25.1.3.18 SetValueInBuffer (arrayBuffer,byteIndex,type,value,isTypedArray,order [ ,isLittleEndian ] )
The abstract operation SetValueInBuffer takes argumentsarrayBuffer (an ArrayBuffer or SharedArrayBuffer),byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes inarrayBuffer starting atbyteIndex to represent a value oftype.Assert :valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise,valueis a Number .- Letblock bearrayBuffer.[[ArrayBufferData]].
- LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - IfisLittleEndian is not present, setisLittleEndian to the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - LetrawBytes be
NumericToRawBytes (type,value,isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - IfisTypedArray is
true andIsNoTearConfiguration (type,order) istrue , letnoTear betrue ; otherwise letnoTear befalse . - Append
WriteSharedMemory {[[Order]]:order,[[NoTear]]:noTear,[[Block]]:block,[[ByteIndex]]:byteIndex,[[ElementSize]]:elementSize,[[Payload]]:rawBytes } toeventsRecord.[[EventList]].
- Letexecution be the[[CandidateExecution]] field of the
- Else,
- Store the individual bytes ofrawBytes intoblock, starting atblock[byteIndex].
- Return
unused .
25.1.3.19 GetModifySetValueInBuffer (arrayBuffer,byteIndex,type,value,op )
The abstract operation GetModifySetValueInBuffer takes argumentsarrayBuffer (an ArrayBuffer or a SharedArrayBuffer),byteIndex (a non-negative
Assert :IsDetachedBuffer (arrayBuffer) isfalse .Assert : There are sufficient bytes inarrayBuffer starting atbyteIndex to represent a value oftype.Assert :valueis a BigInt ifIsBigIntElementType (type) istrue ; otherwise,valueis a Number .- Letblock bearrayBuffer.[[ArrayBufferData]].
- LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - LetrawBytes be
NumericToRawBytes (type,value,isLittleEndian). - If
IsSharedArrayBuffer (arrayBuffer) istrue , then- Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - LetrawBytesRead be a
List of lengthelementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations,rawBytesRead is the result of a load-link, of a load-exclusive, or of an operand of a read-modify-write instruction on the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - LetrmwEvent be
ReadModifyWriteSharedMemory {[[Order]]:seq-cst ,[[NoTear]]:true ,[[Block]]:block,[[ByteIndex]]:byteIndex,[[ElementSize]]:elementSize,[[Payload]]:rawBytes,[[ModifyOp]]:op }. - AppendrmwEvent toeventsRecord.[[EventList]].
- Append
Chosen Value Record {[[Event]]:rmwEvent,[[ChosenValue]]:rawBytesRead } toexecution.[[ChosenValues]].
- Letexecution be the[[CandidateExecution]] field of the
- Else,
- LetrawBytesRead be a
List of lengthelementSize whose elements are the sequence ofelementSize bytes starting withblock[byteIndex]. - LetrawBytesModified beop(rawBytesRead,rawBytes).
- Store the individual bytes ofrawBytesModified intoblock, starting atblock[byteIndex].
- LetrawBytesRead be a
- Return
RawBytesToNumeric (type,rawBytesRead,isLittleEndian).
25.1.4 The ArrayBuffer Constructor
The ArrayBuffer
- is%ArrayBuffer%.
- is the initial value of the
"ArrayBuffer" property of theglobal object . - creates and initializes a new ArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified ArrayBuffer behaviour must include asupercall to the ArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theArrayBuffer.prototypebuilt-in methods.
25.1.4.1 ArrayBuffer (length [ ,options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - LetbyteLength be ?
ToIndex (length). - LetrequestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateArrayBuffer (NewTarget,byteLength,requestedMaxByteLength).
25.1.5 Properties of the ArrayBuffer Constructor
The ArrayBuffer
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.1.5.1 ArrayBuffer.isView (arg )
This function performs the following steps when called:
- Ifarg
is not an Object , returnfalse . - Ifarg has a[[ViewedArrayBuffer]] internal slot, return
true . - Return
false .
25.1.5.2 ArrayBuffer.prototype
The initial value ofArrayBuffer.prototype is the
This property has the attributes {[[Writable]]:
25.1.5.3 get ArrayBuffer [ @@species ]
ArrayBuffer[@@species] is an
- Return the
this value.
The value of the
25.1.6 Properties of the ArrayBuffer Prototype Object
TheArrayBuffer prototype object:
- is%ArrayBuffer.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an[[ArrayBufferData]] or[[ArrayBufferByteLength]] internal slot.
25.1.6.1 get ArrayBuffer.prototype.byteLength
ArrayBuffer.prototype.byteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - Letlength beO.[[ArrayBufferByteLength]].
- Return
𝔽 (length).
25.1.6.2 ArrayBuffer.prototype.constructor
The initial value ofArrayBuffer.prototype.constructor is
25.1.6.3 get ArrayBuffer.prototype.detached
ArrayBuffer.prototype.detached is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - Return
IsDetachedBuffer (O).
25.1.6.4 get ArrayBuffer.prototype.maxByteLength
ArrayBuffer.prototype.maxByteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , return+0 𝔽. - If
IsFixedLengthArrayBuffer (O) istrue , then- Letlength beO.[[ArrayBufferByteLength]].
- Else,
- Letlength beO.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.1.6.5 get ArrayBuffer.prototype.resizable
ArrayBuffer.prototype.resizable is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.1.6.6 ArrayBuffer.prototype.resize (newLength )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - LetnewByteLength be ?
ToIndex (newLength). - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - IfnewByteLength >O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - LethostHandled be ?
HostResizeArrayBuffer (O,newByteLength). - IfhostHandled is
handled , returnundefined . - LetoldBlock beO.[[ArrayBufferData]].
- LetnewBlock be ?
CreateByteDataBlock (newByteLength). - LetcopyLength be
min (newByteLength,O.[[ArrayBufferByteLength]]). - Perform
CopyDataBlockBytes (newBlock, 0,oldBlock, 0,copyLength). - NOTE: Neither creation of the new
Data Block nor copying from the oldData Block are observable. Implementations may implement this method as in-place growth or shrinkage. - SetO.[[ArrayBufferData]] tonewBlock.
- SetO.[[ArrayBufferByteLength]] tonewByteLength.
- Return
undefined .
25.1.6.7 ArrayBuffer.prototype.slice (start,end )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) istrue , throw aTypeError exception. - If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - Letlen beO.[[ArrayBufferByteLength]].
- LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letfirst be 0.
- Else ifrelativeStart < 0, letfirst be
max (len +relativeStart, 0). - Else, letfirst be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letfinal be 0.
- Else ifrelativeEnd < 0, letfinal be
max (len +relativeEnd, 0). - Else, letfinal be
min (relativeEnd,len). - LetnewLen be
max (final -first, 0). - Letctor be ?
SpeciesConstructor (O,%ArrayBuffer% ). - Letnew be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) istrue , throw aTypeError exception. - If
IsDetachedBuffer (new) istrue , throw aTypeError exception. - If
SameValue (new,O) istrue , throw aTypeError exception. - Ifnew.[[ArrayBufferByteLength]] <newLen, throw a
TypeError exception. - NOTE: Side-effects of the above steps may have detached or resizedO.
- If
IsDetachedBuffer (O) istrue , throw aTypeError exception. - LetfromBuf beO.[[ArrayBufferData]].
- LettoBuf benew.[[ArrayBufferData]].
- LetcurrentLen beO.[[ArrayBufferByteLength]].
- Iffirst <currentLen, then
- Letcount be
min (newLen,currentLen -first). - Perform
CopyDataBlockBytes (toBuf, 0,fromBuf,first,count).
- Letcount be
- Returnnew.
25.1.6.8 ArrayBuffer.prototype.transfer ( [newLength ] )
This method performs the following steps when called:
- LetO be the
this value. - Return ?
ArrayBufferCopyAndDetach (O,newLength,preserve-resizability ).
25.1.6.9 ArrayBuffer.prototype.transferToFixedLength ( [newLength ] )
This method performs the following steps when called:
- LetO be the
this value. - Return ?
ArrayBufferCopyAndDetach (O,newLength,fixed-length ).
25.1.6.10 ArrayBuffer.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
25.1.7 Properties of ArrayBuffer Instances
ArrayBuffer instances inherit properties from the
ArrayBuffer instances whose[[ArrayBufferData]] is
ArrayBuffer instances whose[[ArrayBufferDetachKey]] is set to a value other than
25.1.8 Resizable ArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differs greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
The following are guidelines for ECMAScript implementers implementing
If a
If a
25.2 SharedArrayBuffer Objects
25.2.1 Fixed-length and Growable SharedArrayBuffer Objects
Afixed-length SharedArrayBuffer is a SharedArrayBuffer whose byte length cannot change after creation.
Agrowable SharedArrayBuffer is a SharedArrayBuffer whose byte length may increase after creation via calls to
The kind of SharedArrayBuffer object that is created depends on the arguments passed to
25.2.2 Abstract Operations for SharedArrayBuffer Objects
25.2.2.1 AllocateSharedArrayBuffer (constructor,byteLength [ ,maxByteLength ] )
The abstract operation AllocateSharedArrayBuffer takes argumentsconstructor (a
- Letslots be «[[ArrayBufferData]] ».
- IfmaxByteLength is present andmaxByteLength is not
empty , letallocatingGrowableBuffer betrue ; otherwise letallocatingGrowableBuffer befalse . - IfallocatingGrowableBuffer is
true , then- IfbyteLength >maxByteLength, throw a
RangeError exception. - Append[[ArrayBufferByteLengthData]] and[[ArrayBufferMaxByteLength]] toslots.
- IfbyteLength >maxByteLength, throw a
- Else,
- Append[[ArrayBufferByteLength]] toslots.
- Letobj be ?
OrdinaryCreateFromConstructor (constructor,"%SharedArrayBuffer.prototype%" ,slots). - IfallocatingGrowableBuffer is
true , letallocLength bemaxByteLength; otherwise letallocLength bebyteLength. - Letblock be ?
CreateSharedByteDataBlock (allocLength). - Setobj.[[ArrayBufferData]] toblock.
- IfallocatingGrowableBuffer is
true , thenAssert :byteLength ≤maxByteLength.- LetbyteLengthBlock be ?
CreateSharedByteDataBlock (8). - Perform
SetValueInBuffer (byteLengthBlock, 0,biguint64 ,ℤ (byteLength),true ,seq-cst ). - Setobj.[[ArrayBufferByteLengthData]] tobyteLengthBlock.
- Setobj.[[ArrayBufferMaxByteLength]] tomaxByteLength.
- Else,
- Setobj.[[ArrayBufferByteLength]] tobyteLength.
- Returnobj.
25.2.2.2 IsSharedArrayBuffer (obj )
The abstract operation IsSharedArrayBuffer takes argumentobj (an ArrayBuffer or a SharedArrayBuffer) and returns a Boolean. It tests whether an object is an ArrayBuffer, a SharedArrayBuffer, or a subtype of either. It performs the following steps when called:
- LetbufferData beobj.[[ArrayBufferData]].
- IfbufferData is
null , returnfalse . - IfbufferData is a
Data Block , returnfalse . Assert :bufferData is aShared Data Block .- Return
true .
25.2.2.3 HostGrowSharedArrayBuffer (buffer,newByteLength )
The
The implementation of HostGrowSharedArrayBuffer must conform to the following requirements:
- If the abstract operation does not complete normally with
unhandled , andnewByteLength < the current byte length of thebuffer ornewByteLength >buffer.[[ArrayBufferMaxByteLength]], throw aRangeError exception. - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . If the abstract operation completes normally withhandled , aWriteSharedMemory orReadModifyWriteSharedMemory event whose[[Order]] isseq-cst ,[[Payload]] isNumericToRawBytes (biguint64 ,newByteLength,isLittleEndian),[[Block]] isbuffer.[[ArrayBufferByteLengthData]],[[ByteIndex]] is 0, and[[ElementSize]] is 8 is added to thesurrounding agent 'scandidate execution such that racing calls toSharedArrayBuffer.prototype.groware not "lost", i.e. silently do nothing.
The second requirement above is intentionally vague about how or when the current byte length ofbuffer is read. Because the byte length must be updated via an atomic read-modify-write operation on the underlying hardware, architectures that use load-link/store-conditional or load-exclusive/store-exclusive instruction pairs may wish to keep the paired instructions close in the instruction stream. As such, SharedArrayBuffer.prototype.grow itself does not perform bounds checking onnewByteLength before calling HostGrowSharedArrayBuffer, nor is there a requirement on when the current byte length is read.
This is in contrast with
The default implementation of HostGrowSharedArrayBuffer is to return
25.2.3 The SharedArrayBuffer Constructor
The SharedArrayBuffer
- is%SharedArrayBuffer%.
- is the initial value of the
"SharedArrayBuffer" property of theglobal object , if that property is present (see below). - creates and initializes a new SharedArrayBuffer when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified SharedArrayBuffer behaviour must include asupercall to the SharedArrayBufferconstructor to create and initialize subclass instances with the internal state necessary to support theSharedArrayBuffer.prototypebuilt-in methods.
Whenever a
Unlike anArrayBuffer, aSharedArrayBuffer cannot become detached, and its internal[[ArrayBufferData]] slot is never
25.2.3.1 SharedArrayBuffer (length [ ,options ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - LetbyteLength be ?
ToIndex (length). - LetrequestedMaxByteLength be ?
GetArrayBufferMaxByteLengthOption (options). - Return ?
AllocateSharedArrayBuffer (NewTarget,byteLength,requestedMaxByteLength).
25.2.4 Properties of the SharedArrayBuffer Constructor
The SharedArrayBuffer
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.2.4.1 SharedArrayBuffer.prototype
The initial value ofSharedArrayBuffer.prototype is the
This property has the attributes {[[Writable]]:
25.2.4.2 get SharedArrayBuffer [ @@species ]
SharedArrayBuffer[@@species] is an
- Return the
this value.
The value of the
25.2.5 Properties of the SharedArrayBuffer Prototype Object
TheSharedArrayBuffer prototype object:
- is%SharedArrayBuffer.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have an[[ArrayBufferData]] or[[ArrayBufferByteLength]] internal slot.
25.2.5.1 get SharedArrayBuffer.prototype.byteLength
SharedArrayBuffer.prototype.byteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Letlength be
ArrayBufferByteLength (O,seq-cst ). - Return
𝔽 (length).
25.2.5.2 SharedArrayBuffer.prototype.constructor
The initial value ofSharedArrayBuffer.prototype.constructor is
25.2.5.3 SharedArrayBuffer.prototype.grow (newLength )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferMaxByteLength]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - LetnewByteLength be ?
ToIndex (newLength). - LethostHandled be ?
HostGrowSharedArrayBuffer (O,newByteLength). - IfhostHandled is
handled , returnundefined . - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - LetbyteLengthBlock beO.[[ArrayBufferByteLengthData]].
- LetcurrentByteLengthRawBytes be
GetRawBytesFromSharedBlock (byteLengthBlock, 0,biguint64 ,true ,seq-cst ). - LetnewByteLengthRawBytes be
NumericToRawBytes (biguint64 ,ℤ (newByteLength),isLittleEndian). - Repeat,
- NOTE: This is a compare-and-exchange loop to ensure that parallel, racing grows of the same buffer are totally ordered, are not lost, and do not silently do nothing. The loop exits if it was able to attempt to grow uncontended.
- LetcurrentByteLength be
ℝ (RawBytesToNumeric (biguint64 ,currentByteLengthRawBytes,isLittleEndian)). - IfnewByteLength =currentByteLength, return
undefined . - IfnewByteLength <currentByteLength ornewByteLength >O.[[ArrayBufferMaxByteLength]], throw a
RangeError exception. - LetbyteLengthDelta benewByteLength -currentByteLength.
- If it is impossible to create a new
Shared Data Block value consisting ofbyteLengthDelta bytes, throw aRangeError exception. - NOTE: No new
Shared Data Block is constructed and used here. The observable behaviour of growable SharedArrayBuffers is specified by allocating amax -sizedShared Data Block at construction time, and this step captures the requirement that implementations that run out of memory must throw aRangeError . - LetreadByteLengthRawBytes be
AtomicCompareExchangeInSharedBlock (byteLengthBlock, 0, 8,currentByteLengthRawBytes,newByteLengthRawBytes). - If
ByteListEqual (readByteLengthRawBytes,currentByteLengthRawBytes) istrue , returnundefined . - SetcurrentByteLengthRawBytes toreadByteLengthRawBytes.
Spurious failures of the compare-exchange to update the length are prohibited. If the bounds checking for the new length passes and the implementation is not out of memory, a
Parallel calls to SharedArrayBuffer.prototype.grow are totally ordered. For example, consider two racing calls:sab.grow(10) andsab.grow(20). One of the two calls is guaranteed to win the race. The call tosab.grow(10) will never shrinksab even ifsab.grow(20) happened first; in that case it will instead throw a RangeError.
25.2.5.4 get SharedArrayBuffer.prototype.growable
SharedArrayBuffer.prototype.growable is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) isfalse , returntrue ; otherwise returnfalse .
25.2.5.5 get SharedArrayBuffer.prototype.maxByteLength
SharedArrayBuffer.prototype.maxByteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - If
IsFixedLengthArrayBuffer (O) istrue , then- Letlength beO.[[ArrayBufferByteLength]].
- Else,
- Letlength beO.[[ArrayBufferMaxByteLength]].
- Return
𝔽 (length).
25.2.5.6 SharedArrayBuffer.prototype.slice (start,end )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (O) isfalse , throw aTypeError exception. - Letlen be
ArrayBufferByteLength (O,seq-cst ). - LetrelativeStart be ?
ToIntegerOrInfinity (start). - IfrelativeStart = -∞, letfirst be 0.
- Else ifrelativeStart < 0, letfirst be
max (len +relativeStart, 0). - Else, letfirst be
min (relativeStart,len). - Ifend is
undefined , letrelativeEnd belen; else letrelativeEnd be ?ToIntegerOrInfinity (end). - IfrelativeEnd = -∞, letfinal be 0.
- Else ifrelativeEnd < 0, letfinal be
max (len +relativeEnd, 0). - Else, letfinal be
min (relativeEnd,len). - LetnewLen be
max (final -first, 0). - Letctor be ?
SpeciesConstructor (O,%SharedArrayBuffer% ). - Letnew be ?
Construct (ctor, «𝔽 (newLen) »). - Perform ?
RequireInternalSlot (new,[[ArrayBufferData]]). - If
IsSharedArrayBuffer (new) isfalse , throw aTypeError exception. - Ifnew.[[ArrayBufferData]] isO.[[ArrayBufferData]], throw a
TypeError exception. - If
ArrayBufferByteLength (new,seq-cst ) <newLen, throw aTypeError exception. - LetfromBuf beO.[[ArrayBufferData]].
- LettoBuf benew.[[ArrayBufferData]].
- Perform
CopyDataBlockBytes (toBuf, 0,fromBuf,first,newLen). - Returnnew.
25.2.5.7 SharedArrayBuffer.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
25.2.6 Properties of SharedArrayBuffer Instances
SharedArrayBuffer instances inherit properties from the
SharedArrayBuffer instances, unlike ArrayBuffer instances, are never detached.
25.2.7 Growable SharedArrayBuffer Guidelines
The following are guidelines for ECMAScript programmers working with
We recommend that programs be tested in their deployment environments where possible. The amount of available physical memory differ greatly between hardware devices. Similarly, virtual memory subsystems also differ greatly between hardware devices as well as operating systems. An application that runs without out-of-memory errors on a 64-bit desktop web browser could run out of memory on a 32-bit mobile web browser.
When choosing a value for the
Please note that successfully constructing a
Not all loads of au8[idx], are not synchronizing. In general, in the absence of explicit synchronization, one property access being in-bound does not imply a subsequent property access in the samelength andbyteLength getters on SharedArrayBuffer,
The following are guidelines for ECMAScript implementers implementing
We recommend
Because grow operations can happen in parallel with memory accesses on a
Grown memory must appear zeroed from the moment of its creation, including to any racy accesses in parallel. This can be accomplished via zero-filled-on-demand virtual memory pages, or careful synchronization if manually zeroing memory.
In practice it is difficult to implement
25.3 DataView Objects
25.3.1 Abstract Operations For DataView Objects
25.3.1.1 DataView With Buffer Witness Records
ADataView With Buffer Witness Record is a
DataView With Buffer Witness Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Object]] | a DataView | The DataView object whose buffer's byte length is loaded. |
| [[CachedBufferByteLength]] | a non-negative | The byte length of the object's[[ViewedArrayBuffer]] when the |
25.3.1.2 MakeDataViewWithBufferWitnessRecord (obj,order )
The abstract operation MakeDataViewWithBufferWitnessRecord takes argumentsobj (a DataView) andorder (
- Letbuffer beobj.[[ViewedArrayBuffer]].
- If
IsDetachedBuffer (buffer) istrue , then- LetbyteLength be
detached .
- LetbyteLength be
- Else,
- LetbyteLength be
ArrayBufferByteLength (buffer,order).
- LetbyteLength be
- Return the
DataView With Buffer Witness Record {[[Object]]:obj,[[CachedBufferByteLength]]:byteLength }.
25.3.1.3 GetViewByteLength (viewRecord )
The abstract operation GetViewByteLength takes argumentviewRecord (a
Assert :IsViewOutOfBounds (viewRecord) isfalse .- Letview beviewRecord.[[Object]].
- Ifview.[[ByteLength]] is not
auto , returnview.[[ByteLength]]. Assert :IsFixedLengthArrayBuffer (view.[[ViewedArrayBuffer]]) isfalse .- LetbyteOffset beview.[[ByteOffset]].
- LetbyteLength beviewRecord.[[CachedBufferByteLength]].
Assert :byteLength is notdetached .- ReturnbyteLength -byteOffset.
25.3.1.4 IsViewOutOfBounds (viewRecord )
The abstract operation IsViewOutOfBounds takes argumentviewRecord (a
- Letview beviewRecord.[[Object]].
- LetbufferByteLength beviewRecord.[[CachedBufferByteLength]].
Assert :IsDetachedBuffer (view.[[ViewedArrayBuffer]]) istrue if and only ifbufferByteLength isdetached .- IfbufferByteLength is
detached , returntrue . - LetbyteOffsetStart beview.[[ByteOffset]].
- Ifview.[[ByteLength]] is
auto , then- LetbyteOffsetEnd bebufferByteLength.
- Else,
- LetbyteOffsetEnd bebyteOffsetStart +view.[[ByteLength]].
- IfbyteOffsetStart >bufferByteLength orbyteOffsetEnd >bufferByteLength, return
true . - NOTE: 0-length DataViews are not considered out-of-bounds.
- Return
false .
25.3.1.5 GetViewValue (view,requestIndex,isLittleEndian,type )
The abstract operation GetViewValue takes argumentsview (an
- Perform ?
RequireInternalSlot (view,[[DataView]]). Assert :view has a[[ViewedArrayBuffer]] internal slot.- LetgetIndex be ?
ToIndex (requestIndex). - SetisLittleEndian to
ToBoolean (isLittleEndian). - LetviewOffset beview.[[ByteOffset]].
- LetviewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation whenview's backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - LetviewSize be
GetViewByteLength (viewRecord). - LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - IfgetIndex +elementSize >viewSize, throw a
RangeError exception. - LetbufferIndex begetIndex +viewOffset.
- Return
GetValueFromBuffer (view.[[ViewedArrayBuffer]],bufferIndex,type,false ,unordered ,isLittleEndian).
25.3.1.6 SetViewValue (view,requestIndex,isLittleEndian,type,value )
The abstract operation SetViewValue takes argumentsview (an
- Perform ?
RequireInternalSlot (view,[[DataView]]). Assert :view has a[[ViewedArrayBuffer]] internal slot.- LetgetIndex be ?
ToIndex (requestIndex). - If
IsBigIntElementType (type) istrue , letnumberValue be ?ToBigInt (value). - Otherwise, letnumberValue be ?
ToNumber (value). - SetisLittleEndian to
ToBoolean (isLittleEndian). - LetviewOffset beview.[[ByteOffset]].
- LetviewRecord be
MakeDataViewWithBufferWitnessRecord (view,unordered ). - NOTE: Bounds checking is not a synchronizing operation whenview's backing buffer is a
growable SharedArrayBuffer . - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - LetviewSize be
GetViewByteLength (viewRecord). - LetelementSize be the Element Size value specified in
Table 71 for Element Typetype. - IfgetIndex +elementSize >viewSize, throw a
RangeError exception. - LetbufferIndex begetIndex +viewOffset.
- Perform
SetValueInBuffer (view.[[ViewedArrayBuffer]],bufferIndex,type,numberValue,false ,unordered ,isLittleEndian). - Return
undefined .
25.3.2 The DataView Constructor
The DataView
- is%DataView%.
- is the initial value of the
"DataView" property of theglobal object . - creates and initializes a new DataView when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified DataView behaviour must include asupercall to the DataViewconstructor to create and initialize subclass instances with the internal state necessary to support theDataView.prototypebuilt-in methods.
25.3.2.1 DataView (buffer [ ,byteOffset [ ,byteLength ] ] )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Perform ?
RequireInternalSlot (buffer,[[ArrayBufferData]]). - Letoffset be ?
ToIndex (byteOffset). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - LetbufferByteLength be
ArrayBufferByteLength (buffer,seq-cst ). - Ifoffset >bufferByteLength, throw a
RangeError exception. - LetbufferIsFixedLength be
IsFixedLengthArrayBuffer (buffer). - IfbyteLength is
undefined , then- IfbufferIsFixedLength is
true , then- LetviewByteLength bebufferByteLength -offset.
- Else,
- LetviewByteLength be
auto .
- LetviewByteLength be
- IfbufferIsFixedLength is
- Else,
- LetviewByteLength be ?
ToIndex (byteLength). - Ifoffset +viewByteLength >bufferByteLength, throw a
RangeError exception.
- LetviewByteLength be ?
- LetO be ?
OrdinaryCreateFromConstructor (NewTarget,"%DataView.prototype%" , «[[DataView]],[[ViewedArrayBuffer]],[[ByteLength]],[[ByteOffset]] »). - If
IsDetachedBuffer (buffer) istrue , throw aTypeError exception. - SetbufferByteLength to
ArrayBufferByteLength (buffer,seq-cst ). - Ifoffset >bufferByteLength, throw a
RangeError exception. - IfbyteLength is not
undefined , then- Ifoffset +viewByteLength >bufferByteLength, throw a
RangeError exception.
- Ifoffset +viewByteLength >bufferByteLength, throw a
- SetO.[[ViewedArrayBuffer]] tobuffer.
- SetO.[[ByteLength]] toviewByteLength.
- SetO.[[ByteOffset]] tooffset.
- ReturnO.
25.3.3 Properties of the DataView Constructor
The DataView
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
25.3.3.1 DataView.prototype
The initial value ofDataView.prototype is the
This property has the attributes {[[Writable]]:
25.3.4 Properties of the DataView Prototype Object
TheDataView prototype object:
- is%DataView.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[DataView]],[[ViewedArrayBuffer]],[[ByteLength]], or[[ByteOffset]] internal slot.
25.3.4.1 get DataView.prototype.buffer
DataView.prototype.buffer is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[DataView]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- Letbuffer beO.[[ViewedArrayBuffer]].
- Returnbuffer.
25.3.4.2 get DataView.prototype.byteLength
DataView.prototype.byteLength is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[DataView]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- LetviewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Letsize be
GetViewByteLength (viewRecord). - Return
𝔽 (size).
25.3.4.3 get DataView.prototype.byteOffset
DataView.prototype.byteOffset is an
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[DataView]]). Assert :O has a[[ViewedArrayBuffer]] internal slot.- LetviewRecord be
MakeDataViewWithBufferWitnessRecord (O,seq-cst ). - If
IsViewOutOfBounds (viewRecord) istrue , throw aTypeError exception. - Letoffset beO.[[ByteOffset]].
- Return
𝔽 (offset).
25.3.4.4 DataView.prototype.constructor
The initial value ofDataView.prototype.constructor is
25.3.4.5 DataView.prototype.getBigInt64 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
GetViewValue (v,byteOffset,littleEndian,bigint64 ).
25.3.4.6 DataView.prototype.getBigUint64 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
GetViewValue (v,byteOffset,littleEndian,biguint64 ).
25.3.4.7 DataView.prototype.getFloat32 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,float32 ).
25.3.4.8 DataView.prototype.getFloat64 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,float64 ).
25.3.4.9 DataView.prototype.getInt8 (byteOffset )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
GetViewValue (v,byteOffset,true ,int8 ).
25.3.4.10 DataView.prototype.getInt16 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,int16 ).
25.3.4.11 DataView.prototype.getInt32 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,int32 ).
25.3.4.12 DataView.prototype.getUint8 (byteOffset )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
GetViewValue (v,byteOffset,true ,uint8 ).
25.3.4.13 DataView.prototype.getUint16 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,uint16 ).
25.3.4.14 DataView.prototype.getUint32 (byteOffset [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
GetViewValue (v,byteOffset,littleEndian,uint32 ).
25.3.4.15 DataView.prototype.setBigInt64 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
SetViewValue (v,byteOffset,littleEndian,bigint64 ,value).
25.3.4.16 DataView.prototype.setBigUint64 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
SetViewValue (v,byteOffset,littleEndian,biguint64 ,value).
25.3.4.17 DataView.prototype.setFloat32 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,float32 ,value).
25.3.4.18 DataView.prototype.setFloat64 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,float64 ,value).
25.3.4.19 DataView.prototype.setInt8 (byteOffset,value )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
SetViewValue (v,byteOffset,true ,int8 ,value).
25.3.4.20 DataView.prototype.setInt16 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,int16 ,value).
25.3.4.21 DataView.prototype.setInt32 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,int32 ,value).
25.3.4.22 DataView.prototype.setUint8 (byteOffset,value )
This method performs the following steps when called:
- Letv be the
this value. - Return ?
SetViewValue (v,byteOffset,true ,uint8 ,value).
25.3.4.23 DataView.prototype.setUint16 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,uint16 ,value).
25.3.4.24 DataView.prototype.setUint32 (byteOffset,value [ ,littleEndian ] )
This method performs the following steps when called:
- Letv be the
this value. - IflittleEndian is not present, setlittleEndian to
false . - Return ?
SetViewValue (v,byteOffset,littleEndian,uint32 ,value).
25.3.4.25 DataView.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
25.3.5 Properties of DataView Instances
DataView instances are
The value of the[[DataView]] internal slot is not used within this specification. The simple presence of that internal slot is used within the specification to identify objects created using the DataView
25.4 The Atomics Object
The Atomics object:
- is%Atomics%.
- is the initial value of the
"Atomics" property of theglobal object . - is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a[[Call]] internal method; it cannot be invoked as a function.
The Atomics object provides functions that operate indivisibly (atomically) on shared memory array cells as well as functions that let
For informative guidelines for programming and implementing shared memory in ECMAScript, please see the notes at the end of the
25.4.1 Waiter Record
AWaiter Record is aAtomics.wait orAtomics.waitAsync.
A Waiter Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] | an | TheAtomics.wait orAtomics.waitAsync. |
| [[PromiseCapability]] | a | If denoting a call toAtomics.waitAsync, the resulting promise, otherwise |
| [[TimeoutTime]] | a non-negative | The earliest time by which timeout may be triggered; computed using |
| [[Result]] | The return value of the call. |
25.4.2 WaiterList Records
AWaiterList Record is used to explain waiting and notification ofAtomics.wait,Atomics.waitAsync, andAtomics.notify.
A WaiterList Record has fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Waiters]] | a | The calls toAtomics.wait orAtomics.waitAsync that are waiting on the location with which this WaiterList is associated. |
| [[MostRecentLeaveEvent]] | a | The event of the most recent leaving of its |
There can be multiple
The
Each WaiterList Record has acritical section that controls exclusive access to that WaiterList Record during evaluation. Only a single
25.4.3 Abstract Operations for Atomics
25.4.3.1 ValidateIntegerTypedArray (typedArray,waitable )
The abstract operation ValidateIntegerTypedArray takes argumentstypedArray (an
- LettaRecord be ?
ValidateTypedArray (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation whentypedArray's backing buffer is a
growable SharedArrayBuffer . - Ifwaitable is
true , then- IftypedArray.[[TypedArrayName]] is neither
"Int32Array" nor"BigInt64Array" , throw aTypeError exception.
- IftypedArray.[[TypedArrayName]] is neither
- Else,
- Lettype be
TypedArrayElementType (typedArray). - If
IsUnclampedIntegerElementType (type) isfalse andIsBigIntElementType (type) isfalse , throw aTypeError exception.
- Lettype be
- ReturntaRecord.
25.4.3.2 ValidateAtomicAccess (taRecord,requestIndex )
The abstract operation ValidateAtomicAccess takes argumentstaRecord (a
- Letlength be
TypedArrayLength (taRecord). - LetaccessIndex be ?
ToIndex (requestIndex). Assert :accessIndex ≥ 0.- IfaccessIndex ≥length, throw a
RangeError exception. - LettypedArray betaRecord.[[Object]].
- LetelementSize be
TypedArrayElementSize (typedArray). - Letoffset betypedArray.[[ByteOffset]].
- Return (accessIndex ×elementSize) +offset.
25.4.3.3 ValidateAtomicAccessOnIntegerTypedArray (typedArray,requestIndex [ ,waitable ] )
The abstract operation ValidateAtomicAccessOnIntegerTypedArray takes argumentstypedArray (an
- Ifwaitable is not present, setwaitable to
false . - LettaRecord be ?
ValidateIntegerTypedArray (typedArray,waitable). - Return ?
ValidateAtomicAccess (taRecord,requestIndex).
25.4.3.4 RevalidateAtomicAccess (typedArray,byteIndexInBuffer )
The abstract operation RevalidateAtomicAccess takes argumentstypedArray (a
- LettaRecord be
MakeTypedArrayWithBufferWitnessRecord (typedArray,unordered ). - NOTE: Bounds checking is not a synchronizing operation whentypedArray's backing buffer is a
growable SharedArrayBuffer . - If
IsTypedArrayOutOfBounds (taRecord) istrue , throw aTypeError exception. Assert :byteIndexInBuffer ≥typedArray.[[ByteOffset]].- IfbyteIndexInBuffer ≥taRecord.[[CachedBufferByteLength]], throw a
RangeError exception. - Return
unused .
25.4.3.5 GetWaiterList (block,i )
The abstract operation GetWaiterList takes argumentsblock (a
Assert :i andi + 3 are valid byte offsets within the memory ofblock.- Return the
WaiterList Record that is referenced by the pair (block,i).
25.4.3.6 EnterCriticalSection (WL )
The abstract operation EnterCriticalSection takes argumentWL (a
Assert : Thesurrounding agent is not in thecritical section for anyWaiterList Record .- Wait until no
agent is in thecritical section forWL, then enter thecritical section forWL (without allowing any otheragent to enter). - IfWL.[[MostRecentLeaveEvent]] is not
empty , then- NOTE: AWL whose
critical section has been entered at least once has aSynchronize event set byLeaveCriticalSection . - Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - LetenterEvent be a new
Synchronize event . - AppendenterEvent toeventsRecord.[[EventList]].
- Append (WL.[[MostRecentLeaveEvent]],enterEvent) toeventsRecord.[[AgentSynchronizesWith]].
- NOTE: AWL whose
- Return
unused .
EnterCriticalSection hascontention when an
25.4.3.7 LeaveCriticalSection (WL )
The abstract operation LeaveCriticalSection takes argumentWL (a
Assert : Thesurrounding agent is in thecritical section forWL.- Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - LetleaveEvent be a new
Synchronize event . - AppendleaveEvent toeventsRecord.[[EventList]].
- SetWL.[[MostRecentLeaveEvent]] toleaveEvent.
- Leave the
critical section forWL. - Return
unused .
25.4.3.8 AddWaiter (WL,waiterRecord )
The abstract operation AddWaiter takes argumentsWL (a
Assert : Thesurrounding agent is in thecritical section forWL.Assert : There is noWaiter Record inWL.[[Waiters]] whose[[PromiseCapability]] field iswaiterRecord.[[PromiseCapability]] and whose[[AgentSignifier]] field iswaiterRecord.[[AgentSignifier]].- AppendwaiterRecord toWL.[[Waiters]].
- Return
unused .
25.4.3.9 RemoveWaiter (WL,waiterRecord )
The abstract operation RemoveWaiter takes argumentsWL (a
Assert : Thesurrounding agent is in thecritical section forWL.Assert :WL.[[Waiters]] containswaiterRecord.- RemovewaiterRecord fromWL.[[Waiters]].
- Return
unused .
25.4.3.10 RemoveWaiters (WL,c )
The abstract operation RemoveWaiters takes argumentsWL (a
Assert : Thesurrounding agent is in thecritical section forWL.- Letlen be the number of elements inWL.[[Waiters]].
- Letn be
min (c,len). - LetL be a
List whose elements are the firstn elements ofWL.[[Waiters]]. - Remove the firstn elements ofWL.[[Waiters]].
- ReturnL.
25.4.3.11 SuspendThisAgent (WL,waiterRecord )
The abstract operation SuspendThisAgent takes argumentsWL (a
Assert : Thesurrounding agent is in thecritical section forWL.Assert :WL.[[Waiters]] containswaiterRecord.- LetthisAgent be
AgentSignifier (). Assert :waiterRecord.[[AgentSignifier]] isthisAgent.Assert :waiterRecord.[[PromiseCapability]] isblocking .Assert :AgentCanSuspend () istrue .- Perform
LeaveCriticalSection (WL) and suspend thesurrounding agent until the time iswaiterRecord.[[TimeoutTime]], performing the combined operation in such a way that a notification that arrives after thecritical section is exited but before the suspension takes effect is not lost. Thesurrounding agent can only wake from suspension due to a timeout or due to anotheragent callingNotifyWaiter with argumentsWL andthisAgent (i.e. via a call toAtomics.notify). - Perform
EnterCriticalSection (WL). - Return
unused .
25.4.3.12 NotifyWaiter (WL,waiterRecord )
The abstract operation NotifyWaiter takes argumentsWL (a
Assert : Thesurrounding agent is in thecritical section forWL.- IfwaiterRecord.[[PromiseCapability]] is
blocking , then- Wake the
agent whose signifier iswaiterRecord.[[AgentSignifier]] from suspension. - NOTE: This causes the
agent to resume execution inSuspendThisAgent .
- Wake the
- Else if
AgentSignifier () iswaiterRecord.[[AgentSignifier]], then- LetpromiseCapability bewaiterRecord.[[PromiseCapability]].
- Perform !
Call (promiseCapability.[[Resolve]],undefined , «waiterRecord.[[Result]] »).
- Else,
- Perform
EnqueueResolveInAgentJob (waiterRecord.[[AgentSignifier]],waiterRecord.[[PromiseCapability]],waiterRecord.[[Result]]).
- Perform
- Return
unused .
25.4.3.13 EnqueueResolveInAgentJob (agentSignifier,promiseCapability,resolution )
The abstract operation EnqueueResolveInAgentJob takes argumentsagentSignifier (an
- LetresolveJob be a new
Job Abstract Closure with no parameters that capturesagentSignifier,promiseCapability, andresolution and performs the following steps when called:Assert :AgentSignifier () isagentSignifier.- Perform !
Call (promiseCapability.[[Resolve]],undefined , «resolution »). - Return
unused .
- LetrealmInTargetAgent be !
GetFunctionRealm (promiseCapability.[[Resolve]]). Assert :agentSignifier isrealmInTargetAgent.[[AgentSignifier]].- Perform
HostEnqueueGenericJob (resolveJob,realmInTargetAgent). - Return
unused .
25.4.3.14 DoWait (mode,typedArray,index,value,timeout )
The abstract operation DoWait takes argumentsmode (
- LettaRecord be ?
ValidateIntegerTypedArray (typedArray,true ). - Letbuffer betaRecord.[[Object]].[[ViewedArrayBuffer]].
- If
IsSharedArrayBuffer (buffer) isfalse , throw aTypeError exception. - Leti be ?
ValidateAtomicAccess (taRecord,index). - LetarrayTypeName betypedArray.[[TypedArrayName]].
- IfarrayTypeName is
"BigInt64Array" , letv be ?ToBigInt64 (value). - Else, letv be ?
ToInt32 (value). - Letq be ?
ToNumber (timeout). - Ifq is either
NaN or+∞ 𝔽, lett be +∞; else ifq is-∞ 𝔽, lett be 0; else lett bemax (ℝ (q), 0). - Ifmode is
sync andAgentCanSuspend () isfalse , throw aTypeError exception. - Letblock bebuffer.[[ArrayBufferData]].
- Letoffset betypedArray.[[ByteOffset]].
- LetbyteIndexInBuffer be (i × 4) +offset.
- LetWL be
GetWaiterList (block,byteIndexInBuffer). - Ifmode is
sync , then- LetpromiseCapability be
blocking . - LetresultObject be
undefined .
- LetpromiseCapability be
- Else,
- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetresultObject be
OrdinaryObjectCreate (%Object.prototype% ).
- LetpromiseCapability be !
- Perform
EnterCriticalSection (WL). - LetelementType be
TypedArrayElementType (typedArray). - Letw be
GetValueFromBuffer (buffer,byteIndexInBuffer,elementType,true ,seq-cst ). - Ifv ≠w, then
- Perform
LeaveCriticalSection (WL). - Ifmode is
sync , return"not-equal" . - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"not-equal" ). - ReturnresultObject.
- Perform
- Ift is 0 andmode is
async , then- NOTE: There is no special handling of synchronous immediate timeouts. Asynchronous immediate timeouts have special handling in order to fail fast and avoid unnecessary Promise jobs.
- Perform
LeaveCriticalSection (WL). - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,false ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,"timed-out" ). - ReturnresultObject.
- LetthisAgent be
AgentSignifier (). - Letnow be the
time value (UTC) identifying the current time. - LetadditionalTimeout be an
implementation-defined non-negativemathematical value . - LettimeoutTime be
ℝ (now) +t +additionalTimeout. - NOTE: Whent is +∞,timeoutTime is also +∞.
- LetwaiterRecord be a new
Waiter Record {[[AgentSignifier]]:thisAgent,[[PromiseCapability]]:promiseCapability,[[TimeoutTime]]:timeoutTime,[[Result]]:"ok" }. - Perform
AddWaiter (WL,waiterRecord). - Ifmode is
sync , then- Perform
SuspendThisAgent (WL,waiterRecord).
- Perform
- Else iftimeoutTime is
finite , then- Perform
EnqueueAtomicsWaitAsyncTimeoutJob (WL,waiterRecord).
- Perform
- Perform
LeaveCriticalSection (WL). - Ifmode is
sync , returnwaiterRecord.[[Result]]. - Perform !
CreateDataPropertyOrThrow (resultObject,"async" ,true ). - Perform !
CreateDataPropertyOrThrow (resultObject,"value" ,promiseCapability.[[Promise]]). - ReturnresultObject.
additionalTimeout allows implementations to pad timeouts as necessary, such as for reducing power consumption or coarsening timer resolution to mitigate timing attacks. This value may differ from call to call of DoWait.
25.4.3.15 EnqueueAtomicsWaitAsyncTimeoutJob (WL,waiterRecord )
The abstract operation EnqueueAtomicsWaitAsyncTimeoutJob takes argumentsWL (a
- LettimeoutJob be a new
Job Abstract Closure with no parameters that capturesWL andwaiterRecord and performs the following steps when called:- Perform
EnterCriticalSection (WL). - IfWL.[[Waiters]] containswaiterRecord, then
- LettimeOfJobExecution be the
time value (UTC) identifying the current time. Assert :ℝ (timeOfJobExecution) ≥waiterRecord.[[TimeoutTime]] (ignoring potential non-monotonicity oftime values ).- SetwaiterRecord.[[Result]] to
"timed-out" . - Perform
RemoveWaiter (WL,waiterRecord). - Perform
NotifyWaiter (WL,waiterRecord).
- LettimeOfJobExecution be the
- Perform
LeaveCriticalSection (WL). - Return
unused .
- Perform
- Letnow be the
time value (UTC) identifying the current time. - LetcurrentRealm be
the current Realm Record . - Perform
HostEnqueueTimeoutJob (timeoutJob,currentRealm,𝔽 (waiterRecord.[[TimeoutTime]]) -now). - Return
unused .
25.4.3.16 AtomicCompareExchangeInSharedBlock (block,byteIndexInBuffer,elementSize,expectedBytes,replacementBytes )
The abstract operation AtomicCompareExchangeInSharedBlock takes argumentsblock (a
- Letexecution be the[[CandidateExecution]] field of the
surrounding agent 'sAgent Record . - LeteventsRecord be the
Agent Events Record ofexecution.[[EventsRecords]] whose[[AgentSignifier]] isAgentSignifier (). - LetrawBytesRead be a
List of lengthelementSize whose elements are nondeterministically chosenbyte values . - NOTE: In implementations,rawBytesRead is the result of a load-link, of a load-exclusive, or of an operand of a read-modify-write instruction on the underlying hardware. The nondeterminism is a semantic prescription of the
memory model to describe observable behaviour of hardware with weak consistency. - NOTE: The comparison of the expected value and the read value is performed outside of the
read-modify-write modification function to avoid needlessly strong synchronization when the expected value is not equal to the read value. - If
ByteListEqual (rawBytesRead,expectedBytes) istrue , then- Letsecond be a new
read-modify-write modification function with parameters (oldBytes,newBytes) that captures nothing and performs the following steps atomically when called:- ReturnnewBytes.
- Letevent be
ReadModifyWriteSharedMemory {[[Order]]:seq-cst ,[[NoTear]]:true ,[[Block]]:block,[[ByteIndex]]:byteIndexInBuffer,[[ElementSize]]:elementSize,[[Payload]]:replacementBytes,[[ModifyOp]]:second }.
- Letsecond be a new
- Else,
- Letevent be
ReadSharedMemory {[[Order]]:seq-cst ,[[NoTear]]:true ,[[Block]]:block,[[ByteIndex]]:byteIndexInBuffer,[[ElementSize]]:elementSize }.
- Letevent be
- Appendevent toeventsRecord.[[EventList]].
- Append
Chosen Value Record {[[Event]]:event,[[ChosenValue]]:rawBytesRead } toexecution.[[ChosenValues]]. - ReturnrawBytesRead.
25.4.3.17 AtomicReadModifyWrite (typedArray,index,value,op )
The abstract operation AtomicReadModifyWrite takes argumentstypedArray (an
- LetbyteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray,index). - IftypedArray.[[ContentType]] is
bigint , letv be ?ToBigInt (value). - Otherwise, letv be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray,byteIndexInBuffer). - Letbuffer betypedArray.[[ViewedArrayBuffer]].
- LetelementType be
TypedArrayElementType (typedArray). - Return
GetModifySetValueInBuffer (buffer,byteIndexInBuffer,elementType,v,op).
25.4.3.18 ByteListBitwiseOp (op,xBytes,yBytes )
The abstract operation ByteListBitwiseOp takes argumentsop (&,^, or|),xBytes (a
Assert :xBytes andyBytes have the same number of elements.- Letresult be a new empty
List . - Leti be 0.
- For each elementxByte ofxBytes, do
- LetyByte beyBytes[i].
- Ifop is
&, then- LetresultByte be the result of applying the bitwise AND operation toxByte andyByte.
- Else ifop is
^, then- LetresultByte be the result of applying the bitwise exclusive OR (XOR) operation toxByte andyByte.
- Else,
Assert :op is|.- LetresultByte be the result of applying the bitwise inclusive OR operation toxByte andyByte.
- Seti toi + 1.
- AppendresultByte toresult.
- Returnresult.
25.4.3.19 ByteListEqual (xBytes,yBytes )
The abstract operation ByteListEqual takes argumentsxBytes (a
- IfxBytes andyBytes do not have the same number of elements, return
false . - Leti be 0.
- For each elementxByte ofxBytes, do
- LetyByte beyBytes[i].
- IfxByte ≠yByte, return
false . - Seti toi + 1.
- Return
true .
25.4.4 Atomics.add (typedArray,index,value )
This function performs the following steps when called:
- Lettype be
TypedArrayElementType (typedArray). - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Letadd be a new
read-modify-write modification function with parameters (xBytes,yBytes) that capturestype andisLittleEndian and performs the following steps atomically when called:- Letx be
RawBytesToNumeric (type,xBytes,isLittleEndian). - Lety be
RawBytesToNumeric (type,yBytes,isLittleEndian). - Ifx
is a Number , then- Letsum be
Number::add (x,y).
- Letsum be
- Else,
Assert :xis a BigInt .- Letsum be
BigInt::add (x,y).
- LetsumBytes be
NumericToRawBytes (type,sum,isLittleEndian). Assert :sumBytes,xBytes, andyBytes have the same number of elements.- ReturnsumBytes.
- Letx be
- Return ?
AtomicReadModifyWrite (typedArray,index,value,add).
25.4.5 Atomics.and (typedArray,index,value )
This function performs the following steps when called:
- Letand be a new
read-modify-write modification function with parameters (xBytes,yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (&,xBytes,yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray,index,value,and).
25.4.6 Atomics.compareExchange (typedArray,index,expectedValue,replacementValue )
This function performs the following steps when called:
- LetbyteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray,index). - Letbuffer betypedArray.[[ViewedArrayBuffer]].
- Letblock bebuffer.[[ArrayBufferData]].
- IftypedArray.[[ContentType]] is
bigint , then - Else,
- Letexpected be
𝔽 (?ToIntegerOrInfinity (expectedValue)). - Letreplacement be
𝔽 (?ToIntegerOrInfinity (replacementValue)).
- Letexpected be
- Perform ?
RevalidateAtomicAccess (typedArray,byteIndexInBuffer). - LetelementType be
TypedArrayElementType (typedArray). - LetelementSize be
TypedArrayElementSize (typedArray). - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - LetexpectedBytes be
NumericToRawBytes (elementType,expected,isLittleEndian). - LetreplacementBytes be
NumericToRawBytes (elementType,replacement,isLittleEndian). - If
IsSharedArrayBuffer (buffer) istrue , then- LetrawBytesRead be
AtomicCompareExchangeInSharedBlock (block,byteIndexInBuffer,elementSize,expectedBytes,replacementBytes).
- LetrawBytesRead be
- Else,
- LetrawBytesRead be a
List of lengthelementSize whose elements are the sequence ofelementSize bytes starting withblock[byteIndexInBuffer]. - If
ByteListEqual (rawBytesRead,expectedBytes) istrue , then- Store the individual bytes ofreplacementBytes intoblock, starting atblock[byteIndexInBuffer].
- LetrawBytesRead be a
- Return
RawBytesToNumeric (elementType,rawBytesRead,isLittleEndian).
25.4.7 Atomics.exchange (typedArray,index,value )
This function performs the following steps when called:
- Letsecond be a new
read-modify-write modification function with parameters (oldBytes,newBytes) that captures nothing and performs the following steps atomically when called:- ReturnnewBytes.
- Return ?
AtomicReadModifyWrite (typedArray,index,value,second).
25.4.8 Atomics.isLockFree (size )
This function performs the following steps when called:
- Letn be ?
ToIntegerOrInfinity (size). - LetAR be the
Agent Record of thesurrounding agent . - Ifn = 1, returnAR.[[IsLockFree1]].
- Ifn = 2, returnAR.[[IsLockFree2]].
- Ifn = 4, return
true . - Ifn = 8, returnAR.[[IsLockFree8]].
- Return
false .
This function is an optimization primitive. The intuition is that if the atomic step of an atomic primitive (compareExchange,load,store,add,sub,and,or,xor, orexchange) on a datum of sizen bytes will be performed without theAtomics.isLockFree(n) will return
Atomics.isLockFree(4) always returns
Regardless of the value returned by this function, all atomic operations are guaranteed to be atomic. For example, they will never have a visible operation take place in the middle of the operation (e.g., "tearing").
25.4.9 Atomics.load (typedArray,index )
This function performs the following steps when called:
- LetbyteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray,index). - Perform ?
RevalidateAtomicAccess (typedArray,byteIndexInBuffer). - Letbuffer betypedArray.[[ViewedArrayBuffer]].
- LetelementType be
TypedArrayElementType (typedArray). - Return
GetValueFromBuffer (buffer,byteIndexInBuffer,elementType,true ,seq-cst ).
25.4.10 Atomics.or (typedArray,index,value )
This function performs the following steps when called:
- Letor be a new
read-modify-write modification function with parameters (xBytes,yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (|,xBytes,yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray,index,value,or).
25.4.11 Atomics.store (typedArray,index,value )
This function performs the following steps when called:
- LetbyteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray,index). - IftypedArray.[[ContentType]] is
bigint , letv be ?ToBigInt (value). - Otherwise, letv be
𝔽 (?ToIntegerOrInfinity (value)). - Perform ?
RevalidateAtomicAccess (typedArray,byteIndexInBuffer). - Letbuffer betypedArray.[[ViewedArrayBuffer]].
- LetelementType be
TypedArrayElementType (typedArray). - Perform
SetValueInBuffer (buffer,byteIndexInBuffer,elementType,v,true ,seq-cst ). - Returnv.
25.4.12 Atomics.sub (typedArray,index,value )
This function performs the following steps when called:
- Lettype be
TypedArrayElementType (typedArray). - LetisLittleEndian be the value of the[[LittleEndian]] field of the
surrounding agent 'sAgent Record . - Letsubtract be a new
read-modify-write modification function with parameters (xBytes,yBytes) that capturestype andisLittleEndian and performs the following steps atomically when called:- Letx be
RawBytesToNumeric (type,xBytes,isLittleEndian). - Lety be
RawBytesToNumeric (type,yBytes,isLittleEndian). - Ifx
is a Number , then- Letdifference be
Number::subtract (x,y).
- Letdifference be
- Else,
Assert :xis a BigInt .- Letdifference be
BigInt::subtract (x,y).
- LetdifferenceBytes be
NumericToRawBytes (type,difference,isLittleEndian). Assert :differenceBytes,xBytes, andyBytes have the same number of elements.- ReturndifferenceBytes.
- Letx be
- Return ?
AtomicReadModifyWrite (typedArray,index,value,subtract).
25.4.13 Atomics.wait (typedArray,index,value,timeout )
This function puts the
It performs the following steps when called:
- Return ?
DoWait (sync ,typedArray,index,value,timeout).
25.4.14 Atomics.waitAsync (typedArray,index,value,timeout )
This function returns a Promise that is resolved when the calling
It performs the following steps when called:
- Return ?
DoWait (async ,typedArray,index,value,timeout).
25.4.15 Atomics.notify (typedArray,index,count )
This function notifies some
It performs the following steps when called:
- LetbyteIndexInBuffer be ?
ValidateAtomicAccessOnIntegerTypedArray (typedArray,index,true ). - Ifcount is
undefined , then- Letc be +∞.
- Else,
- LetintCount be ?
ToIntegerOrInfinity (count). - Letc be
max (intCount, 0).
- LetintCount be ?
- Letbuffer betypedArray.[[ViewedArrayBuffer]].
- Letblock bebuffer.[[ArrayBufferData]].
- If
IsSharedArrayBuffer (buffer) isfalse , return+0 𝔽. - LetWL be
GetWaiterList (block,byteIndexInBuffer). - Perform
EnterCriticalSection (WL). - LetS be
RemoveWaiters (WL,c). - For each elementW ofS, do
- Perform
NotifyWaiter (WL,W).
- Perform
- Perform
LeaveCriticalSection (WL). - Letn be the number of elements inS.
- Return
𝔽 (n).
25.4.16 Atomics.xor (typedArray,index,value )
This function performs the following steps when called:
- Letxor be a new
read-modify-write modification function with parameters (xBytes,yBytes) that captures nothing and performs the following steps atomically when called:- Return
ByteListBitwiseOp (^,xBytes,yBytes).
- Return
- Return ?
AtomicReadModifyWrite (typedArray,index,value,xor).
25.4.17 Atomics [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
25.5 The JSON Object
The JSON object:
- is%JSON%.
- is the initial value of the
"JSON" property of theglobal object . - is an
ordinary object . - contains two functions,
parseandstringify, that are used to parse and construct JSON texts. - has a[[Prototype]] internal slot whose value is
%Object.prototype% . - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a[[Call]] internal method; it cannot be invoked as a function.
The JSON Data Interchange Format is defined in ECMA-404. The JSON interchange format used in this specification is exactly that described by ECMA-404. Conforming implementations ofJSON.parse andJSON.stringify must support the exact interchange format described in the ECMA-404 specification without any deletions or extensions to the format.
25.5.1 JSON.parse (text [ ,reviver ] )
This function parses a JSON text (a JSON-formatted String) and produces an
The optionalreviver parameter is a function that takes two parameters,key andvalue. It can filter and transform the results. It is called with each of thekey/value pairs produced by the parse, and its return value is used instead of the original value. If it returns what it received, the structure is not modified. If it returns
- LetjsonString be ?
ToString (text). - Parse
StringToCodePoints (jsonString) as a JSON text as specified in ECMA-404. Throw aSyntaxError exception if it is not a valid JSON text as defined in that specification. - LetscriptString be the
string-concatenation of"(" ,jsonString, and");" . - Letscript be
ParseText (StringToCodePoints (scriptString),Script ). - NOTE: The
early error rules defined in13.2.5.1 have special handling for the above invocation ofParseText . Assert :script is aParse Node .- Letcompletion be
Completion (Evaluation ofscript). - NOTE: The
PropertyDefinitionEvaluation semantics defined in13.2.5.5 have special handling for the above evaluation. - Letunfiltered becompletion.[[Value]].
Assert :unfiltered is either a String, a Number, a Boolean, an Object that is defined by either anArrayLiteral or anObjectLiteral , ornull .- If
IsCallable (reviver) istrue , then- Letroot be
OrdinaryObjectCreate (%Object.prototype% ). - LetrootName be the empty String.
- Perform !
CreateDataPropertyOrThrow (root,rootName,unfiltered). - Return ?
InternalizeJSONProperty (root,rootName,reviver).
- Letroot be
- Else,
- Returnunfiltered.
The
Valid JSON text is a subset of the ECMAScript
However, becauseJSON.parse, the same source text can produce different results when evaluated as aJSON.parse, means that not all texts accepted byJSON.parse are valid as a
25.5.1.1 InternalizeJSONProperty (holder,name,reviver )
The abstract operation InternalizeJSONProperty takes argumentsholder (an Object),name (a String), andreviver (a
This algorithm intentionally does not throw an exception if either[[Delete]] or
It performs the following steps when called:
- Letval be ?
Get (holder,name). - Ifval
is an Object , then- LetisArray be ?
IsArray (val). - IfisArray is
true , then- Letlen be ?
LengthOfArrayLike (val). - LetI be 0.
- Repeat, whileI <len,
- Letprop be !
ToString (𝔽 (I)). - LetnewElement be ?
InternalizeJSONProperty (val,prop,reviver). - IfnewElement is
undefined , then- Perform ? val.[[Delete]](prop).
- Else,
- Perform ?
CreateDataProperty (val,prop,newElement).
- Perform ?
- SetI toI + 1.
- Letprop be !
- Letlen be ?
- Else,
- Letkeys be ?
EnumerableOwnProperties (val,key ). - For each StringP ofkeys, do
- LetnewElement be ?
InternalizeJSONProperty (val,P,reviver). - IfnewElement is
undefined , then- Perform ? val.[[Delete]](P).
- Else,
- Perform ?
CreateDataProperty (val,P,newElement).
- Perform ?
- LetnewElement be ?
- Letkeys be ?
- LetisArray be ?
- Return ?
Call (reviver,holder, «name,val »).
It is not permitted for a conforming implementation ofJSON.parse to extend the JSON grammars. If an implementation wishes to support a modified or extended JSON interchange format it must do so by defining a different parse function.
In the case where there are duplicate name Strings within an object, lexically preceding values for the same key shall be overwritten.
25.5.2 JSON.stringify (value [ ,replacer [ ,space ] ] )
This function returns a String in UTF-16 encoded JSON format representing an
It performs the following steps when called:
- Letstack be a new empty
List . - Letindent be the empty String.
- LetPropertyList be
undefined . - LetReplacerFunction be
undefined . - Ifreplacer
is an Object , then- If
IsCallable (replacer) istrue , then- SetReplacerFunction toreplacer.
- Else,
- LetisArray be ?
IsArray (replacer). - IfisArray is
true , then- SetPropertyList to a new empty
List . - Letlen be ?
LengthOfArrayLike (replacer). - Letk be 0.
- Repeat, whilek <len,
- Letprop be !
ToString (𝔽 (k)). - Letv be ?
Get (replacer,prop). - Letitem be
undefined . - Ifv
is a String , then- Setitem tov.
- Else ifv
is a Number , then- Setitem to !
ToString (v).
- Setitem to !
- Else ifv
is an Object , then- Ifv has a[[StringData]] or[[NumberData]] internal slot, setitem to ?
ToString (v).
- Ifv has a[[StringData]] or[[NumberData]] internal slot, setitem to ?
- Ifitem is not
undefined andPropertyList does not containitem, then- Appenditem toPropertyList.
- Setk tok + 1.
- Letprop be !
- SetPropertyList to a new empty
- LetisArray be ?
- If
- Ifspace
is an Object , then - Ifspace
is a Number , then- LetspaceMV be !
ToIntegerOrInfinity (space). - SetspaceMV to
min (10,spaceMV). - IfspaceMV < 1, letgap be the empty String; otherwise letgap be the String value containingspaceMV occurrences of the code unit 0x0020 (SPACE).
- LetspaceMV be !
- Else ifspace
is a String , then- If the length ofspace ≤ 10, letgap bespace; otherwise letgap be the
substring ofspace from 0 to 10.
- If the length ofspace ≤ 10, letgap bespace; otherwise letgap be the
- Else,
- Letgap be the empty String.
- Letwrapper be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (wrapper, the empty String,value). - Letstate be the
JSON Serialization Record {[[ReplacerFunction]]:ReplacerFunction,[[Stack]]:stack,[[Indent]]:indent,[[Gap]]:gap,[[PropertyList]]:PropertyList }. - Return ?
SerializeJSONProperty (state, the empty String,wrapper).
The
JSON structures are allowed to be nested to any depth, but they must be acyclic. Ifvalue is or contains a cyclic structure, then this function must throw a
a = [];a[0] = a;my_text =JSON.stringify(a);// This must throw a TypeError.Symbolic primitive values are rendered as follows:
- The
null value is rendered in JSON text as the String value"null" . - The
undefined value is not rendered. - The
true value is rendered in JSON text as the String value"true" . - The
false value is rendered in JSON text as the String value"false" .
String values are wrapped in QUOTATION MARK (") code units. The code units" and\ are escaped with\ prefixes. Control characters code units are replaced with escape sequences\uHHHH, or with the shorter forms,\b (BACKSPACE),\f (FORM FEED),\n (LINE FEED),\r (CARRIAGE RETURN),\t (CHARACTER TABULATION).
Values that do not have a JSON representation (such as
An object is rendered as U+007B (LEFT CURLY BRACKET) followed by zero or more properties, separated with a U+002C (COMMA), closed with a U+007D (RIGHT CURLY BRACKET). A property is a quoted String representing the
25.5.2.1 JSON Serialization Record
AJSON Serialization Record is a
JSON Serialization Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[ReplacerFunction]] | a | A function that can supply replacement values for object properties (from JSON.stringify'sreplacer parameter). |
| [[PropertyList]] | either a | The names of properties to include when serializing a non-array object (from JSON.stringify'sreplacer parameter). |
| [[Gap]] | a String | The unit of indentation (from JSON.stringify'sspace parameter). |
| [[Stack]] | a | The set of nested objects that are in the process of being serialized. Used to detect cyclic structures. |
| [[Indent]] | a String | The current indentation. |
25.5.2.2 SerializeJSONProperty (state,key,holder )
The abstract operation SerializeJSONProperty takes argumentsstate (a
- Letvalue be ?
Get (holder,key). - Ifvalue
is an Object orvalueis a BigInt , then- LettoJSON be ?
GetV (value,"toJSON" ). - If
IsCallable (toJSON) istrue , then- Setvalue to ?
Call (toJSON,value, «key »).
- Setvalue to ?
- LettoJSON be ?
- Ifstate.[[ReplacerFunction]] is not
undefined , then- Setvalue to ?
Call (state.[[ReplacerFunction]],holder, «key,value »).
- Setvalue to ?
- Ifvalue
is an Object , then- Ifvalue has a[[NumberData]] internal slot, then
- Setvalue to ?
ToNumber (value).
- Setvalue to ?
- Else ifvalue has a[[StringData]] internal slot, then
- Setvalue to ?
ToString (value).
- Setvalue to ?
- Else ifvalue has a[[BooleanData]] internal slot, then
- Setvalue tovalue.[[BooleanData]].
- Else ifvalue has a[[BigIntData]] internal slot, then
- Setvalue tovalue.[[BigIntData]].
- Ifvalue has a[[NumberData]] internal slot, then
- Ifvalue is
null , return"null" . - Ifvalue is
true , return"true" . - Ifvalue is
false , return"false" . - Ifvalue
is a String , returnQuoteJSONString (value). - Ifvalue
is a Number , then - Ifvalue
is a BigInt , throw aTypeError exception. - Ifvalue
is an Object andIsCallable (value) isfalse , then- LetisArray be ?
IsArray (value). - IfisArray is
true , return ?SerializeJSONArray (state,value). - Return ?
SerializeJSONObject (state,value).
- LetisArray be ?
- Return
undefined .
25.5.2.3 QuoteJSONString (value )
The abstract operation QuoteJSONString takes argumentvalue (a String) and returns a String. It wrapsvalue in 0x0022 (QUOTATION MARK) code units and escapes certain other code units within it. This operation interpretsvalue as a sequence of UTF-16 encoded code points, as described in
- Letproduct be the String value consisting solely of the code unit 0x0022 (QUOTATION MARK).
- For each code pointC of
StringToCodePoints (value), do- IfC is listed in the “Code Point” column of
Table 76 , then- Setproduct to the
string-concatenation ofproduct and the escape sequence forC as specified in the “Escape Sequence” column of the corresponding row.
- Setproduct to the
- Else ifC has a numeric value less than 0x0020 (SPACE) orC has the same numeric value as a
leading surrogate ortrailing surrogate , then- Letunit be the code unit whose numeric value is the numeric value ofC.
- Setproduct to the
string-concatenation ofproduct andUnicodeEscape (unit).
- Else,
- Setproduct to the
string-concatenation ofproduct andUTF16EncodeCodePoint (C).
- Setproduct to the
- IfC is listed in the “Code Point” column of
- Setproduct to the
string-concatenation ofproduct and the code unit 0x0022 (QUOTATION MARK). - Returnproduct.
| Code Point | Unicode Character Name | Escape Sequence |
|---|---|---|
| U+0008 | BACKSPACE | \b |
| U+0009 | CHARACTER TABULATION | \t |
| U+000A | LINE FEED (LF) | \n |
| U+000C | FORM FEED (FF) | \f |
| U+000D | CARRIAGE RETURN (CR) | \r |
| U+0022 | QUOTATION MARK | \" |
| U+005C | REVERSE SOLIDUS | \\ |
25.5.2.4 UnicodeEscape (C )
The abstract operation UnicodeEscape takes argumentC (a code unit) and returns a String. It representsC as a Unicode escape sequence. It performs the following steps when called:
- Letn be the numeric value ofC.
Assert :n ≤ 0xFFFF.- Lethex be the String representation ofn, formatted as a lowercase hexadecimal number.
- Return the
string-concatenation of the code unit 0x005C (REVERSE SOLIDUS),"u" , andStringPad (hex, 4,"0" ,start ).
25.5.2.5 SerializeJSONObject (state,value )
The abstract operation SerializeJSONObject takes argumentsstate (a
- Ifstate.[[Stack]] containsvalue, throw a
TypeError exception because the structure is cyclical. - Appendvalue tostate.[[Stack]].
- Letstepback bestate.[[Indent]].
- Setstate.[[Indent]] to the
string-concatenation ofstate.[[Indent]] andstate.[[Gap]]. - Ifstate.[[PropertyList]] is not
undefined , then- LetK bestate.[[PropertyList]].
- Else,
- LetK be ?
EnumerableOwnProperties (value,key ).
- LetK be ?
- Letpartial be a new empty
List . - For each elementP ofK, do
- LetstrP be ?
SerializeJSONProperty (state,P,value). - IfstrP is not
undefined , then- Letmember be
QuoteJSONString (P). - Setmember to the
string-concatenation ofmember and":" . - Ifstate.[[Gap]] is not the empty String, then
- Setmember to the
string-concatenation ofmember and the code unit 0x0020 (SPACE).
- Setmember to the
- Setmember to the
string-concatenation ofmember andstrP. - Appendmember topartial.
- Letmember be
- LetstrP be ?
- Ifpartial is empty, then
- Letfinal be
"{}" .
- Letfinal be
- Else,
- Ifstate.[[Gap]] is the empty String, then
- Letproperties be the String value formed by concatenating all the element Strings ofpartial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Letfinal be the
string-concatenation of"{" ,properties, and"}" .
- Else,
- Letseparator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), andstate.[[Indent]]. - Letproperties be the String value formed by concatenating all the element Strings ofpartial with each adjacent pair of Strings separated withseparator. Theseparator String is not inserted either before the first String or after the last String.
- Letfinal be the
string-concatenation of"{" , the code unit 0x000A (LINE FEED),state.[[Indent]],properties, the code unit 0x000A (LINE FEED),stepback, and"}" .
- Letseparator be the
- Ifstate.[[Gap]] is the empty String, then
- Remove the last element ofstate.[[Stack]].
- Setstate.[[Indent]] tostepback.
- Returnfinal.
25.5.2.6 SerializeJSONArray (state,value )
The abstract operation SerializeJSONArray takes argumentsstate (a
- Ifstate.[[Stack]] containsvalue, throw a
TypeError exception because the structure is cyclical. - Appendvalue tostate.[[Stack]].
- Letstepback bestate.[[Indent]].
- Setstate.[[Indent]] to the
string-concatenation ofstate.[[Indent]] andstate.[[Gap]]. - Letpartial be a new empty
List . - Letlen be ?
LengthOfArrayLike (value). - Letindex be 0.
- Repeat, whileindex <len,
- LetstrP be ?
SerializeJSONProperty (state, !ToString (𝔽 (index)),value). - IfstrP is
undefined , then- Append
"null" topartial.
- Append
- Else,
- AppendstrP topartial.
- Setindex toindex + 1.
- LetstrP be ?
- Ifpartial is empty, then
- Letfinal be
"[]" .
- Letfinal be
- Else,
- Ifstate.[[Gap]] is the empty String, then
- Letproperties be the String value formed by concatenating all the element Strings ofpartial with each adjacent pair of Strings separated with the code unit 0x002C (COMMA). A comma is not inserted either before the first String or after the last String.
- Letfinal be the
string-concatenation of"[" ,properties, and"]" .
- Else,
- Letseparator be the
string-concatenation of the code unit 0x002C (COMMA), the code unit 0x000A (LINE FEED), andstate.[[Indent]]. - Letproperties be the String value formed by concatenating all the element Strings ofpartial with each adjacent pair of Strings separated withseparator. Theseparator String is not inserted either before the first String or after the last String.
- Letfinal be the
string-concatenation of"[" , the code unit 0x000A (LINE FEED),state.[[Indent]],properties, the code unit 0x000A (LINE FEED),stepback, and"]" .
- Letseparator be the
- Ifstate.[[Gap]] is the empty String, then
- Remove the last element ofstate.[[Stack]].
- Setstate.[[Indent]] tostepback.
- Returnfinal.
The representation of arrays includes only the elements in thearray.length (exclusive). Properties whose keys are not
25.5.3 JSON [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
26 Managing Memory
26.1 WeakRef Objects
A
26.1.1 The WeakRef Constructor
TheWeakRef
- is%WeakRef%.
- is the initial value of the
"WeakRef" property of theglobal object . - creates and initializes a new WeakRef when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedWeakRefbehaviour must include asupercall to theWeakRefconstructor to create and initialize the subclass instance with the internal state necessary to support theWeakRef.prototypebuilt-in methods.
26.1.1.1 WeakRef (target )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - LetweakRef be ?
OrdinaryCreateFromConstructor (NewTarget,"%WeakRef.prototype%" , «[[WeakRefTarget]] »). - Perform
AddToKeptObjects (target). - SetweakRef.[[WeakRefTarget]] totarget.
- ReturnweakRef.
26.1.2 Properties of the WeakRef Constructor
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.1.2.1 WeakRef.prototype
The initial value ofWeakRef.prototype is the
This property has the attributes {[[Writable]]:
26.1.3 Properties of the WeakRef Prototype Object
TheWeakRef prototype object:
- is%WeakRef.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[WeakRefTarget]] internal slot.
26.1.3.1 WeakRef.prototype.constructor
The initial value ofWeakRef.prototype.constructor is
This property has the attributes {[[Writable]]:
26.1.3.2 WeakRef.prototype.deref ( )
This method performs the following steps when called:
- LetweakRef be the
this value. - Perform ?
RequireInternalSlot (weakRef,[[WeakRefTarget]]). - Return
WeakRefDeref (weakRef).
If the
let target = {foo() {} };let weakRef =newWeakRef(target);// ... later ...if (weakRef.deref()) { weakRef.deref().foo();}In the above example, if the first deref does not evaluate to
26.1.3.3 WeakRef.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
26.1.4 WeakRef Abstract Operations
26.1.4.1 WeakRefDeref (weakRef )
The abstract operation WeakRefDeref takes argumentweakRef (a
- Lettarget beweakRef.[[WeakRefTarget]].
- Iftarget is not
empty , then- Perform
AddToKeptObjects (target). - Returntarget.
- Perform
- Return
undefined .
This abstract operation is defined separately from WeakRef.prototype.deref strictly to make it possible to succinctly define liveness.
26.1.5 Properties of WeakRef Instances
26.2 FinalizationRegistry Objects
A
26.2.1 The FinalizationRegistry Constructor
TheFinalizationRegistry
- is%FinalizationRegistry%.
- is the initial value of the
"FinalizationRegistry" property of theglobal object . - creates and initializes a new FinalizationRegistry when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specifiedFinalizationRegistrybehaviour must include asupercall to theFinalizationRegistryconstructor to create and initialize the subclass instance with the internal state necessary to support theFinalizationRegistry.prototypebuilt-in methods.
26.2.1.1 FinalizationRegistry (cleanupCallback )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (cleanupCallback) isfalse , throw aTypeError exception. - LetfinalizationRegistry be ?
OrdinaryCreateFromConstructor (NewTarget,"%FinalizationRegistry.prototype%" , «[[Realm]],[[CleanupCallback]],[[Cells]] »). - Letfn be the
active function object . - SetfinalizationRegistry.[[Realm]] tofn.[[Realm]].
- SetfinalizationRegistry.[[CleanupCallback]] to
HostMakeJobCallback (cleanupCallback). - SetfinalizationRegistry.[[Cells]] to a new empty
List . - ReturnfinalizationRegistry.
26.2.2 Properties of the FinalizationRegistry Constructor
The
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
26.2.2.1 FinalizationRegistry.prototype
The initial value ofFinalizationRegistry.prototype is the
This property has the attributes {[[Writable]]:
26.2.3 Properties of the FinalizationRegistry Prototype Object
TheFinalizationRegistry prototype object:
- is%FinalizationRegistry.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have[[Cells]] and[[CleanupCallback]] internal slots.
26.2.3.1 FinalizationRegistry.prototype.constructor
The initial value ofFinalizationRegistry.prototype.constructor is
26.2.3.2 FinalizationRegistry.prototype.register (target,heldValue [ ,unregisterToken ] )
This method performs the following steps when called:
- LetfinalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry,[[Cells]]). - If
CanBeHeldWeakly (target) isfalse , throw aTypeError exception. - If
SameValue (target,heldValue) istrue , throw aTypeError exception. - If
CanBeHeldWeakly (unregisterToken) isfalse , then- IfunregisterToken is not
undefined , throw aTypeError exception. - SetunregisterToken to
empty .
- IfunregisterToken is not
- Letcell be the
Record {[[WeakRefTarget]]:target,[[HeldValue]]:heldValue,[[UnregisterToken]]:unregisterToken }. - Appendcell tofinalizationRegistry.[[Cells]].
- Return
undefined .
Based on the algorithms and definitions in this specification,cell.[[HeldValue]] is
26.2.3.3 FinalizationRegistry.prototype.unregister (unregisterToken )
This method performs the following steps when called:
- LetfinalizationRegistry be the
this value. - Perform ?
RequireInternalSlot (finalizationRegistry,[[Cells]]). - If
CanBeHeldWeakly (unregisterToken) isfalse , throw aTypeError exception. - Letremoved be
false . - For each
Record {[[WeakRefTarget]],[[HeldValue]],[[UnregisterToken]] }cell offinalizationRegistry.[[Cells]], do- Ifcell.[[UnregisterToken]] is not
empty andSameValue (cell.[[UnregisterToken]],unregisterToken) istrue , then- Removecell fromfinalizationRegistry.[[Cells]].
- Setremoved to
true .
- Ifcell.[[UnregisterToken]] is not
- Returnremoved.
26.2.3.4 FinalizationRegistry.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
26.2.4 Properties of FinalizationRegistry Instances
27 Control Abstraction Objects
27.1 Iteration
27.1.1 Common Iteration Interfaces
An interface is a set of
27.1.1.1 TheIterable Interface
TheIterable interface includes the property described in
| Property | Value | Requirements |
|---|---|---|
@@iterator | a function that returns anIterator object | The returned object must conform to theIterator interface. |
27.1.1.2 TheIterator Interface
An object that implements theIterator interface must include the property in
| Property | Value | Requirements |
|---|---|---|
| a function that returns anIteratorResult object | The returned object must conform to theIteratorResult interface. If a previous call to thenext method of anIterator has returned anIteratorResult object whosenext method of that object should also return anIteratorResult object whose |
Arguments may be passed to thenext function but their interpretation and validity is dependent upon the targetIterator. The for-of statement and other common users ofIterators do not pass any arguments, soIterator objects that expect to be used in such a manner must be prepared to deal with being called with no arguments.
| Property | Value | Requirements |
|---|---|---|
| a function that returns anIteratorResult object | The returned object must conform to theIteratorResult interface. Invoking this method notifies theIterator object that the caller does not intend to make any morenext method calls to theIterator. The returnedIteratorResult object will typically have areturn method. However, this requirement is not enforced. | |
| a function that returns anIteratorResult object | The returned object must conform to theIteratorResult interface. Invoking this method notifies theIterator object that the caller has detected an error condition. The argument may be used to identify the error condition and typically will be an exception object. A typical response is tothrow the value passed as the argument. If the method does notthrow, the returnedIteratorResult object will typically have a |
Typically callers of these methods should check for their existence before invoking them. Certain ECMAScript language features includingfor-of,yield*, and array destructuring call these methods after performing an existence check. Most ECMAScript library functions that acceptIterable objects as arguments also conditionally call them.
27.1.1.3 TheAsyncIterable Interface
TheAsyncIterable interface includes the properties described in
| Property | Value | Requirements |
|---|---|---|
@@asyncIterator | a function that returns anAsyncIterator object | The returned object must conform to theAsyncIterator interface. |
27.1.1.4 TheAsyncIterator Interface
An object that implements theAsyncIterator interface must include the properties in
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for anIteratorResult object | The returned promise, when fulfilled, must fulfill with an object that conforms to theIteratorResult interface. If a previous call to the Additionally, theIteratorResult object that serves as a fulfillment value should have a |
Arguments may be passed to thenext function but their interpretation and validity is dependent upon the targetAsyncIterator. Thefor-await-of statement and other common users ofAsyncIterators do not pass any arguments, soAsyncIterator objects that expect to be used in such a manner must be prepared to deal with being called with no arguments.
| Property | Value | Requirements |
|---|---|---|
| a function that returns a promise for anIteratorResult object | The returned promise, when fulfilled, must fulfill with an object that conforms to theIteratorResult interface. Invoking this method notifies theAsyncIterator object that the caller does not intend to make any more Additionally, theIteratorResult object that serves as a fulfillment value should have a | |
| a function that returns a promise for anIteratorResult object | The returned promise, when fulfilled, must fulfill with an object that conforms to theIteratorResult interface. Invoking this method notifies theAsyncIterator object that the caller has detected an error condition. The argument may be used to identify the error condition and typically will be an exception object. A typical response is to return a rejected promise which rejects with the value passed as the argument. If the returned promise is fulfilled, theIteratorResult fulfillment value will typically have a |
Typically callers of these methods should check for their existence before invoking them. Certain ECMAScript language features includingfor-await-of andyield* call these methods after performing an existence check.
27.1.1.5 TheIteratorResult Interface
TheIteratorResult interface includes the properties listed in
| Property | Value | Requirements |
|---|---|---|
| a Boolean | This is the result status of aniteratornext method call. If the end of the iterator was reached | |
| an | If done is |
27.1.2 The %IteratorPrototype% Object
The%IteratorPrototype% object:
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the Iterator interface also inherit from %IteratorPrototype%. ECMAScript code may also define objects that inherit from %IteratorPrototype%. The %IteratorPrototype% object provides a place where additional methods that are applicable to all iterator objects may be added.
The following expression is one way that ECMAScript code can access the %IteratorPrototype% object:
Object.getPrototypeOf(Object.getPrototypeOf([][Symbol.iterator]()))27.1.2.1 %IteratorPrototype% [ @@iterator ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.3 The %AsyncIteratorPrototype% Object
The%AsyncIteratorPrototype% object:
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object .
All objects defined in this specification that implement the AsyncIterator interface also inherit from %AsyncIteratorPrototype%. ECMAScript code may also define objects that inherit from %AsyncIteratorPrototype%. The %AsyncIteratorPrototype% object provides a place where additional methods that are applicable to all async iterator objects may be added.
27.1.3.1 %AsyncIteratorPrototype% [ @@asyncIterator ] ( )
This function performs the following steps when called:
- Return the
this value.
The value of the
27.1.4 Async-from-Sync Iterator Objects
An Async-from-Sync Iterator object is an async iterator that adapts a specific synchronous iterator. There is not a named
27.1.4.1 CreateAsyncFromSyncIterator (syncIteratorRecord )
The abstract operation CreateAsyncFromSyncIterator takes argumentsyncIteratorRecord (an
- LetasyncIterator be
OrdinaryObjectCreate (%AsyncFromSyncIteratorPrototype% , «[[SyncIteratorRecord]] »). - SetasyncIterator.[[SyncIteratorRecord]] tosyncIteratorRecord.
- LetnextMethod be !
Get (asyncIterator,"next" ). - LetiteratorRecord be the
Iterator Record {[[Iterator]]:asyncIterator,[[NextMethod]]:nextMethod,[[Done]]:false }. - ReturniteratorRecord.
27.1.4.2 The %AsyncFromSyncIteratorPrototype% Object
The%AsyncFromSyncIteratorPrototype% object:
- has properties that are inherited by all Async-from-Sync Iterator Objects.
- is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - has the following properties:
27.1.4.2.1 %AsyncFromSyncIteratorPrototype%.next ( [value ] )
- LetO be the
this value. Assert :Ois an Object that has a[[SyncIteratorRecord]] internal slot.- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetsyncIteratorRecord beO.[[SyncIteratorRecord]].
- Ifvalue is present, then
- Letresult be
Completion (IteratorNext (syncIteratorRecord,value)).
- Letresult be
- Else,
- Letresult be
Completion (IteratorNext (syncIteratorRecord)).
- Letresult be
IfAbruptRejectPromise (result,promiseCapability).- Return
AsyncFromSyncIteratorContinuation (result,promiseCapability).
27.1.4.2.2 %AsyncFromSyncIteratorPrototype%.return ( [value ] )
- LetO be the
this value. Assert :Ois an Object that has a[[SyncIteratorRecord]] internal slot.- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetsyncIterator beO.[[SyncIteratorRecord]].[[Iterator]].
- Letreturn be
Completion (GetMethod (syncIterator,"return" )). IfAbruptRejectPromise (return,promiseCapability).- Ifreturn is
undefined , then- LetiterResult be
CreateIterResultObject (value,true ). - Perform !
Call (promiseCapability.[[Resolve]],undefined , «iterResult »). - ReturnpromiseCapability.[[Promise]].
- LetiterResult be
- Ifvalue is present, then
- Letresult be
Completion (Call (return,syncIterator, «value »)).
- Letresult be
- Else,
- Letresult be
Completion (Call (return,syncIterator)).
- Letresult be
IfAbruptRejectPromise (result,promiseCapability).- Ifresult
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - ReturnpromiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result,promiseCapability).
27.1.4.2.3 %AsyncFromSyncIteratorPrototype%.throw ( [value ] )
- LetO be the
this value. Assert :Ois an Object that has a[[SyncIteratorRecord]] internal slot.- LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - LetsyncIterator beO.[[SyncIteratorRecord]].[[Iterator]].
- Letthrow be
Completion (GetMethod (syncIterator,"throw" )). IfAbruptRejectPromise (throw,promiseCapability).- Ifthrow is
undefined , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «value »). - ReturnpromiseCapability.[[Promise]].
- Perform !
- Ifvalue is present, then
- Letresult be
Completion (Call (throw,syncIterator, «value »)).
- Letresult be
- Else,
- Letresult be
Completion (Call (throw,syncIterator)).
- Letresult be
IfAbruptRejectPromise (result,promiseCapability).- Ifresult
is not an Object , then- Perform !
Call (promiseCapability.[[Reject]],undefined , « a newly createdTypeError object »). - ReturnpromiseCapability.[[Promise]].
- Perform !
- Return
AsyncFromSyncIteratorContinuation (result,promiseCapability).
27.1.4.3 Properties of Async-from-Sync Iterator Instances
Async-from-Sync Iterator instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[SyncIteratorRecord]] | an | Represents the original synchronous iterator which is being adapted. |
27.1.4.4 AsyncFromSyncIteratorContinuation (result,promiseCapability )
The abstract operation AsyncFromSyncIteratorContinuation takes argumentsresult (an Object) andpromiseCapability (a
- NOTE: BecausepromiseCapability is derived from the intrinsic
%Promise% , the calls topromiseCapability.[[Reject]] entailed by the useIfAbruptRejectPromise below are guaranteed not to throw. - Letdone be
Completion (IteratorComplete (result)). IfAbruptRejectPromise (done,promiseCapability).- Letvalue be
Completion (IteratorValue (result)). IfAbruptRejectPromise (value,promiseCapability).- LetvalueWrapper be
Completion (PromiseResolve (%Promise% ,value)). IfAbruptRejectPromise (valueWrapper,promiseCapability).- Letunwrap be a new
Abstract Closure with parameters (v) that capturesdone and performs the following steps when called:- Return
CreateIterResultObject (v,done).
- Return
- LetonFulfilled be
CreateBuiltinFunction (unwrap, 1,"" , « »). - NOTE:onFulfilled is used when processing the
"value" property of an IteratorResult object in order to wait for its value if it is a promise and re-package the result in a new "unwrapped" IteratorResult object. - Perform
PerformPromiseThen (valueWrapper,onFulfilled,undefined ,promiseCapability). - ReturnpromiseCapability.[[Promise]].
27.2 Promise Objects
A Promise is an object that is used as a placeholder for the eventual results of a deferred (and possibly asynchronous) computation.
Any Promise is in one of three mutually exclusive states:fulfilled,rejected, andpending:
- A promise
pis fulfilled ifp.then(f, r)will immediately enqueue aJob to call the functionf. - A promise
pis rejected ifp.then(f, r)will immediately enqueue aJob to call the functionr. - A promise is pending if it is neither fulfilled nor rejected.
A promise is said to besettled if it is not pending, i.e. if it is either fulfilled or rejected.
A promise isresolved if it is settled or if it has been “locked in” to match the state of another promise. Attempting to resolve or reject a resolved promise has no effect. A promise isunresolved if it is not resolved. An unresolved promise is always in the pending state. A resolved promise may be pending, fulfilled or rejected.
27.2.1 Promise Abstract Operations
27.2.1.1 PromiseCapability Records
APromiseCapability Record is a
PromiseCapability Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Promise]] | an Object | An object that is usable as a promise. |
| [[Resolve]] | a | The function that is used to resolve the given promise. |
| [[Reject]] | a | The function that is used to reject the given promise. |
27.2.1.1.1 IfAbruptRejectPromise (value,capability )
IfAbruptRejectPromise is a shorthand for a sequence of algorithm steps that use a
IfAbruptRejectPromise (value,capability).
means the same thing as:
Assert :value is aCompletion Record .- Ifvalue is an
abrupt completion , then- Perform ?
Call (capability.[[Reject]],undefined , «value.[[Value]] »). - Returncapability.[[Promise]].
- Perform ?
- Else,
- Setvalue to ! value.
27.2.1.2 PromiseReaction Records
APromiseReaction Record is a
PromiseReaction Records have the fields listed in
| Field Name | Value | Meaning |
|---|---|---|
| [[Capability]] | a | The capabilities of the promise for which this record provides a reaction handler. |
| [[Type]] | The[[Type]] is used when[[Handler]] is | |
| [[Handler]] | a | The function that should be applied to the incoming value, and whose return value will govern what happens to the derived promise. If[[Handler]] is |
27.2.1.3 CreateResolvingFunctions (promise )
The abstract operation CreateResolvingFunctions takes argumentpromise (a Promise) and returns a
- LetalreadyResolved be the
Record {[[Value]]:false }. - LetstepsResolve be the algorithm steps defined in
Promise Resolve Functions . - LetlengthResolve be the number of non-optional parameters of the function definition in
Promise Resolve Functions . - Letresolve be
CreateBuiltinFunction (stepsResolve,lengthResolve,"" , «[[Promise]],[[AlreadyResolved]] »). - Setresolve.[[Promise]] topromise.
- Setresolve.[[AlreadyResolved]] toalreadyResolved.
- LetstepsReject be the algorithm steps defined in
Promise Reject Functions . - LetlengthReject be the number of non-optional parameters of the function definition in
Promise Reject Functions . - Letreject be
CreateBuiltinFunction (stepsReject,lengthReject,"" , «[[Promise]],[[AlreadyResolved]] »). - Setreject.[[Promise]] topromise.
- Setreject.[[AlreadyResolved]] toalreadyResolved.
- Return the
Record {[[Resolve]]:resolve,[[Reject]]:reject }.
27.2.1.3.1 Promise Reject Functions
A promise reject function is an anonymous built-in function that has[[Promise]] and[[AlreadyResolved]] internal slots.
When a promise reject function is called with argumentreason, the following steps are taken:
- LetF be the
active function object . Assert :F has a[[Promise]] internal slot whose valueis an Object .- Letpromise beF.[[Promise]].
- LetalreadyResolved beF.[[AlreadyResolved]].
- IfalreadyResolved.[[Value]] is
true , returnundefined . - SetalreadyResolved.[[Value]] to
true . - Perform
RejectPromise (promise,reason). - Return
undefined .
The
27.2.1.3.2 Promise Resolve Functions
A promise resolve function is an anonymous built-in function that has[[Promise]] and[[AlreadyResolved]] internal slots.
When a promise resolve function is called with argumentresolution, the following steps are taken:
- LetF be the
active function object . Assert :F has a[[Promise]] internal slot whose valueis an Object .- Letpromise beF.[[Promise]].
- LetalreadyResolved beF.[[AlreadyResolved]].
- IfalreadyResolved.[[Value]] is
true , returnundefined . - SetalreadyResolved.[[Value]] to
true . - If
SameValue (resolution,promise) istrue , then- LetselfResolutionError be a newly created
TypeError object. - Perform
RejectPromise (promise,selfResolutionError). - Return
undefined .
- LetselfResolutionError be a newly created
- Ifresolution
is not an Object , then- Perform
FulfillPromise (promise,resolution). - Return
undefined .
- Perform
- Letthen be
Completion (Get (resolution,"then" )). - Ifthen is an
abrupt completion , then- Perform
RejectPromise (promise,then.[[Value]]). - Return
undefined .
- Perform
- LetthenAction bethen.[[Value]].
- If
IsCallable (thenAction) isfalse , then- Perform
FulfillPromise (promise,resolution). - Return
undefined .
- Perform
- LetthenJobCallback be
HostMakeJobCallback (thenAction). - Letjob be
NewPromiseResolveThenableJob (promise,resolution,thenJobCallback). - Perform
HostEnqueuePromiseJob (job.[[Job]],job.[[Realm]]). - Return
undefined .
The
27.2.1.4 FulfillPromise (promise,value )
The abstract operation FulfillPromise takes argumentspromise (a Promise) andvalue (an
Assert : The value ofpromise.[[PromiseState]] ispending .- Letreactions bepromise.[[PromiseFulfillReactions]].
- Setpromise.[[PromiseResult]] tovalue.
- Setpromise.[[PromiseFulfillReactions]] to
undefined . - Setpromise.[[PromiseRejectReactions]] to
undefined . - Setpromise.[[PromiseState]] to
fulfilled . - Perform
TriggerPromiseReactions (reactions,value). - Return
unused .
27.2.1.5 NewPromiseCapability (C )
The abstract operation NewPromiseCapability takes argumentC (anresolve andreject functions. The promise plus theresolve andreject functions are used to initialize a new
- If
IsConstructor (C) isfalse , throw aTypeError exception. - NOTE:C is assumed to be a
constructor function that supports the parameter conventions of the Promiseconstructor (see27.2.3.1 ). - LetresolvingFunctions be the
Record {[[Resolve]]:undefined ,[[Reject]]:undefined }. - LetexecutorClosure be a new
Abstract Closure with parameters (resolve,reject) that capturesresolvingFunctions and performs the following steps when called:- IfresolvingFunctions.[[Resolve]] is not
undefined , throw aTypeError exception. - IfresolvingFunctions.[[Reject]] is not
undefined , throw aTypeError exception. - SetresolvingFunctions.[[Resolve]] toresolve.
- SetresolvingFunctions.[[Reject]] toreject.
- Return
undefined .
- IfresolvingFunctions.[[Resolve]] is not
- Letexecutor be
CreateBuiltinFunction (executorClosure, 2,"" , « »). - Letpromise be ?
Construct (C, «executor »). - If
IsCallable (resolvingFunctions.[[Resolve]]) isfalse , throw aTypeError exception. - If
IsCallable (resolvingFunctions.[[Reject]]) isfalse , throw aTypeError exception. - Return the
PromiseCapability Record {[[Promise]]:promise,[[Resolve]]:resolvingFunctions.[[Resolve]],[[Reject]]:resolvingFunctions.[[Reject]] }.
This abstract operation supports Promise subclassing, as it is generic on any
27.2.1.6 IsPromise (x )
The abstract operation IsPromise takes argumentx (an
- Ifx
is not an Object , returnfalse . - Ifx does not have a[[PromiseState]] internal slot, return
false . - Return
true .
27.2.1.7 RejectPromise (promise,reason )
The abstract operation RejectPromise takes argumentspromise (a Promise) andreason (an
Assert : The value ofpromise.[[PromiseState]] ispending .- Letreactions bepromise.[[PromiseRejectReactions]].
- Setpromise.[[PromiseResult]] toreason.
- Setpromise.[[PromiseFulfillReactions]] to
undefined . - Setpromise.[[PromiseRejectReactions]] to
undefined . - Setpromise.[[PromiseState]] to
rejected . - Ifpromise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"reject" ). - Perform
TriggerPromiseReactions (reactions,reason). - Return
unused .
27.2.1.8 TriggerPromiseReactions (reactions,argument )
The abstract operation TriggerPromiseReactions takes argumentsreactions (a
- For each elementreaction ofreactions, do
- Letjob be
NewPromiseReactionJob (reaction,argument). - Perform
HostEnqueuePromiseJob (job.[[Job]],job.[[Realm]]).
- Letjob be
- Return
unused .
27.2.1.9 HostPromiseRejectionTracker (promise,operation )
The
The default implementation of HostPromiseRejectionTracker is to return
HostPromiseRejectionTracker is called in two scenarios:
- When a promise is rejected without any handlers, it is called with itsoperation argument set to
"reject" . - When a handler is added to a rejected promise for the first time, it is called with itsoperation argument set to
"handle" .
A typical implementation of HostPromiseRejectionTracker might try to notify developers of unhandled rejections, while also being careful to notify them if such previous notifications are later invalidated by new handlers being attached.
Ifoperation is
27.2.2 Promise Jobs
27.2.2.1 NewPromiseReactionJob (reaction,argument )
The abstract operation NewPromiseReactionJob takes argumentsreaction (a
- Letjob be a new
Job Abstract Closure with no parameters that capturesreaction andargument and performs the following steps when called:- LetpromiseCapability bereaction.[[Capability]].
- Lettype bereaction.[[Type]].
- Lethandler bereaction.[[Handler]].
- Ifhandler is
empty , then- Iftype is
fulfill , then- LethandlerResult be
NormalCompletion (argument).
- LethandlerResult be
- Else,
Assert :type isreject .- LethandlerResult be
ThrowCompletion (argument).
- Iftype is
- Else,
- LethandlerResult be
Completion (HostCallJobCallback (handler,undefined , «argument »)).
- LethandlerResult be
- IfpromiseCapability is
undefined , thenAssert :handlerResult is not anabrupt completion .- Return
empty .
Assert :promiseCapability is aPromiseCapability Record .- IfhandlerResult is an
abrupt completion , then- Return ?
Call (promiseCapability.[[Reject]],undefined , «handlerResult.[[Value]] »).
- Return ?
- Else,
- Return ?
Call (promiseCapability.[[Resolve]],undefined , «handlerResult.[[Value]] »).
- Return ?
- LethandlerRealm be
null . - Ifreaction.[[Handler]] is not
empty , then- LetgetHandlerRealmResult be
Completion (GetFunctionRealm (reaction.[[Handler]].[[Callback]])). - IfgetHandlerRealmResult is a
normal completion , sethandlerRealm togetHandlerRealmResult.[[Value]]. - Else, sethandlerRealm to
the current Realm Record . - NOTE:handlerRealm is never
null unless the handler isundefined . When the handler is a revoked Proxy and no ECMAScript code runs,handlerRealm is used to create error objects.
- LetgetHandlerRealmResult be
- Return the
Record {[[Job]]:job,[[Realm]]:handlerRealm }.
27.2.2.2 NewPromiseResolveThenableJob (promiseToResolve,thenable,then )
The abstract operation NewPromiseResolveThenableJob takes argumentspromiseToResolve (a Promise),thenable (an Object), andthen (a
- Letjob be a new
Job Abstract Closure with no parameters that capturespromiseToResolve,thenable, andthen and performs the following steps when called:- LetresolvingFunctions be
CreateResolvingFunctions (promiseToResolve). - LetthenCallResult be
Completion (HostCallJobCallback (then,thenable, «resolvingFunctions.[[Resolve]],resolvingFunctions.[[Reject]] »)). - IfthenCallResult is an
abrupt completion , then- Return ?
Call (resolvingFunctions.[[Reject]],undefined , «thenCallResult.[[Value]] »).
- Return ?
- Return ? thenCallResult.
- LetresolvingFunctions be
- LetgetThenRealmResult be
Completion (GetFunctionRealm (then.[[Callback]])). - IfgetThenRealmResult is a
normal completion , letthenRealm begetThenRealmResult.[[Value]]. - Else, letthenRealm be
the current Realm Record . - NOTE:thenRealm is never
null . Whenthen.[[Callback]] is a revoked Proxy and no code runs,thenRealm is used to create error objects. - Return the
Record {[[Job]]:job,[[Realm]]:thenRealm }.
27.2.3 The Promise Constructor
The Promise
- is%Promise%.
- is the initial value of the
"Promise" property of theglobal object . - creates and initializes a new Promise when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
- may be used as the value in an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified Promise behaviour must include asupercall to the Promiseconstructor to create and initialize the subclass instance with the internal state necessary to support thePromiseandPromise.prototypebuilt-in methods.
27.2.3.1 Promise (executor )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - If
IsCallable (executor) isfalse , throw aTypeError exception. - Letpromise be ?
OrdinaryCreateFromConstructor (NewTarget,"%Promise.prototype%" , «[[PromiseState]],[[PromiseResult]],[[PromiseFulfillReactions]],[[PromiseRejectReactions]],[[PromiseIsHandled]] »). - Setpromise.[[PromiseState]] to
pending . - Setpromise.[[PromiseFulfillReactions]] to a new empty
List . - Setpromise.[[PromiseRejectReactions]] to a new empty
List . - Setpromise.[[PromiseIsHandled]] to
false . - LetresolvingFunctions be
CreateResolvingFunctions (promise). - Letcompletion be
Completion (Call (executor,undefined , «resolvingFunctions.[[Resolve]],resolvingFunctions.[[Reject]] »)). - Ifcompletion is an
abrupt completion , then- Perform ?
Call (resolvingFunctions.[[Reject]],undefined , «completion.[[Value]] »).
- Perform ?
- Returnpromise.
Theexecutor argument must be a
Theresolve function that is passed to anexecutor function accepts a single argument. Theexecutor code may eventually call theresolve function to indicate that it wishes to resolve the associated Promise. The argument passed to theresolve function represents the eventual value of the deferred action and can be either the actual fulfillment value or another promise which will provide the value if it is fulfilled.
Thereject function that is passed to anexecutor function accepts a single argument. Theexecutor code may eventually call thereject function to indicate that the associated Promise is rejected and will never be fulfilled. The argument passed to thereject function is used as the rejection value of the promise. Typically it will be an Error object.
The resolve and reject functions passed to anexecutor function by the Promise
27.2.4 Properties of the Promise Constructor
The Promise
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - has the following properties:
27.2.4.1 Promise.all (iterable )
This function returns a new promise which is fulfilled with an array of fulfillment values for the passed promises, or rejects with the reason of the first passed promise that rejects. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - LetpromiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve,promiseCapability).- LetiteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord,promiseCapability).- Letresult be
Completion (PerformPromiseAll (iteratorRecord,C,promiseCapability,promiseResolve)). - Ifresult is an
abrupt completion , then- IfiteratorRecord.[[Done]] is
false , setresult toCompletion (IteratorClose (iteratorRecord,result)). IfAbruptRejectPromise (result,promiseCapability).
- IfiteratorRecord.[[Done]] is
- Return ? result.
This function requires its
27.2.4.1.1 GetPromiseResolve (promiseConstructor )
The abstract operation GetPromiseResolve takes argumentpromiseConstructor (a
- LetpromiseResolve be ?
Get (promiseConstructor,"resolve" ). - If
IsCallable (promiseResolve) isfalse , throw aTypeError exception. - ReturnpromiseResolve.
27.2.4.1.2 PerformPromiseAll (iteratorRecord,constructor,resultCapability,promiseResolve )
The abstract operation PerformPromiseAll takes argumentsiteratorRecord (an
- Letvalues be a new empty
List . - LetremainingElementsCount be the
Record {[[Value]]: 1 }. - Letindex be 0.
- Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- LetvaluesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , «valuesArray »).
- LetvaluesArray be
- ReturnresultCapability.[[Promise]].
- Append
undefined tovalues. - LetnextPromise be ?
Call (promiseResolve,constructor, «next »). - Letsteps be the algorithm steps defined in
Promise.allResolve Element Functions - Letlength be the number of non-optional parameters of the function definition in
Promise.allResolve Element Functions - LetonFulfilled be
CreateBuiltinFunction (steps,length,"" , «[[AlreadyCalled]],[[Index]],[[Values]],[[Capability]],[[RemainingElements]] »). - SetonFulfilled.[[AlreadyCalled]] to
false . - SetonFulfilled.[[Index]] toindex.
- SetonFulfilled.[[Values]] tovalues.
- SetonFulfilled.[[Capability]] toresultCapability.
- SetonFulfilled.[[RemainingElements]] toremainingElementsCount.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , «onFulfilled,resultCapability.[[Reject]] »). - Setindex toindex + 1.
- Letnext be ?
27.2.4.1.3Promise.all Resolve Element Functions
APromise.all resolve element function is an anonymous built-in function that is used to resolve a specificPromise.all element. EachPromise.all resolve element function has[[Index]],[[Values]],[[Capability]],[[RemainingElements]], and[[AlreadyCalled]] internal slots.
When aPromise.all resolve element function is called with argumentx, the following steps are taken:
- LetF be the
active function object . - IfF.[[AlreadyCalled]] is
true , returnundefined . - SetF.[[AlreadyCalled]] to
true . - Letindex beF.[[Index]].
- Letvalues beF.[[Values]].
- LetpromiseCapability beF.[[Capability]].
- LetremainingElementsCount beF.[[RemainingElements]].
- Setvalues[index] tox.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- LetvaluesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , «valuesArray »).
- LetvaluesArray be
- Return
undefined .
ThePromise.all resolve element function is
27.2.4.2 Promise.allSettled (iterable )
This function returns a promise that is fulfilled with an array of promise state snapshots, but only after all the original promises have settled, i.e. become either fulfilled or rejected. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - LetpromiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve,promiseCapability).- LetiteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord,promiseCapability).- Letresult be
Completion (PerformPromiseAllSettled (iteratorRecord,C,promiseCapability,promiseResolve)). - Ifresult is an
abrupt completion , then- IfiteratorRecord.[[Done]] is
false , setresult toCompletion (IteratorClose (iteratorRecord,result)). IfAbruptRejectPromise (result,promiseCapability).
- IfiteratorRecord.[[Done]] is
- Return ? result.
This function requires its
27.2.4.2.1 PerformPromiseAllSettled (iteratorRecord,constructor,resultCapability,promiseResolve )
The abstract operation PerformPromiseAllSettled takes argumentsiteratorRecord (an
- Letvalues be a new empty
List . - LetremainingElementsCount be the
Record {[[Value]]: 1 }. - Letindex be 0.
- Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- LetvaluesArray be
CreateArrayFromList (values). - Perform ?
Call (resultCapability.[[Resolve]],undefined , «valuesArray »).
- LetvaluesArray be
- ReturnresultCapability.[[Promise]].
- Append
undefined tovalues. - LetnextPromise be ?
Call (promiseResolve,constructor, «next »). - LetstepsFulfilled be the algorithm steps defined in
Promise.allSettledResolve Element Functions - LetlengthFulfilled be the number of non-optional parameters of the function definition in
Promise.allSettledResolve Element Functions - LetonFulfilled be
CreateBuiltinFunction (stepsFulfilled,lengthFulfilled,"" , «[[AlreadyCalled]],[[Index]],[[Values]],[[Capability]],[[RemainingElements]] »). - LetalreadyCalled be the
Record {[[Value]]:false }. - SetonFulfilled.[[AlreadyCalled]] toalreadyCalled.
- SetonFulfilled.[[Index]] toindex.
- SetonFulfilled.[[Values]] tovalues.
- SetonFulfilled.[[Capability]] toresultCapability.
- SetonFulfilled.[[RemainingElements]] toremainingElementsCount.
- LetstepsRejected be the algorithm steps defined in
Promise.allSettledReject Element Functions - LetlengthRejected be the number of non-optional parameters of the function definition in
Promise.allSettledReject Element Functions - LetonRejected be
CreateBuiltinFunction (stepsRejected,lengthRejected,"" , «[[AlreadyCalled]],[[Index]],[[Values]],[[Capability]],[[RemainingElements]] »). - SetonRejected.[[AlreadyCalled]] toalreadyCalled.
- SetonRejected.[[Index]] toindex.
- SetonRejected.[[Values]] tovalues.
- SetonRejected.[[Capability]] toresultCapability.
- SetonRejected.[[RemainingElements]] toremainingElementsCount.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , «onFulfilled,onRejected »). - Setindex toindex + 1.
- Letnext be ?
27.2.4.2.2Promise.allSettled Resolve Element Functions
APromise.allSettled resolve element function is an anonymous built-in function that is used to resolve a specificPromise.allSettled element. EachPromise.allSettled resolve element function has[[Index]],[[Values]],[[Capability]],[[RemainingElements]], and[[AlreadyCalled]] internal slots.
When aPromise.allSettled resolve element function is called with argumentx, the following steps are taken:
- LetF be the
active function object . - LetalreadyCalled beF.[[AlreadyCalled]].
- IfalreadyCalled.[[Value]] is
true , returnundefined . - SetalreadyCalled.[[Value]] to
true . - Letindex beF.[[Index]].
- Letvalues beF.[[Values]].
- LetpromiseCapability beF.[[Capability]].
- LetremainingElementsCount beF.[[RemainingElements]].
- Letobj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"fulfilled" ). - Perform !
CreateDataPropertyOrThrow (obj,"value" ,x). - Setvalues[index] toobj.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- LetvaluesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , «valuesArray »).
- LetvaluesArray be
- Return
undefined .
ThePromise.allSettled resolve element function is
27.2.4.2.3Promise.allSettled Reject Element Functions
APromise.allSettled reject element function is an anonymous built-in function that is used to reject a specificPromise.allSettled element. EachPromise.allSettled reject element function has[[Index]],[[Values]],[[Capability]],[[RemainingElements]], and[[AlreadyCalled]] internal slots.
When aPromise.allSettled reject element function is called with argumentx, the following steps are taken:
- LetF be the
active function object . - LetalreadyCalled beF.[[AlreadyCalled]].
- IfalreadyCalled.[[Value]] is
true , returnundefined . - SetalreadyCalled.[[Value]] to
true . - Letindex beF.[[Index]].
- Letvalues beF.[[Values]].
- LetpromiseCapability beF.[[Capability]].
- LetremainingElementsCount beF.[[RemainingElements]].
- Letobj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"status" ,"rejected" ). - Perform !
CreateDataPropertyOrThrow (obj,"reason" ,x). - Setvalues[index] toobj.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- LetvaluesArray be
CreateArrayFromList (values). - Return ?
Call (promiseCapability.[[Resolve]],undefined , «valuesArray »).
- LetvaluesArray be
- Return
undefined .
ThePromise.allSettled reject element function is
27.2.4.3 Promise.any (iterable )
This function returns a promise that is fulfilled by the first given promise to be fulfilled, or rejected with anAggregateError holding the rejection reasons if all of the given promises are rejected. It resolves all elements of the passed iterable to promises as it runs this algorithm.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - LetpromiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve,promiseCapability).- LetiteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord,promiseCapability).- Letresult be
Completion (PerformPromiseAny (iteratorRecord,C,promiseCapability,promiseResolve)). - Ifresult is an
abrupt completion , then- IfiteratorRecord.[[Done]] is
false , setresult toCompletion (IteratorClose (iteratorRecord,result)). IfAbruptRejectPromise (result,promiseCapability).
- IfiteratorRecord.[[Done]] is
- Return ? result.
This function requires itsPromise
27.2.4.3.1 PerformPromiseAny (iteratorRecord,constructor,resultCapability,promiseResolve )
The abstract operation PerformPromiseAny takes argumentsiteratorRecord (an
- Leterrors be a new empty
List . - LetremainingElementsCount be the
Record {[[Value]]: 1 }. - Letindex be 0.
- Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- Leterror be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor {[[Configurable]]:true ,[[Enumerable]]:false ,[[Writable]]:true ,[[Value]]:CreateArrayFromList (errors) }). - Return
ThrowCompletion (error).
- Leterror be a newly created
- ReturnresultCapability.[[Promise]].
- Append
undefined toerrors. - LetnextPromise be ?
Call (promiseResolve,constructor, «next »). - LetstepsRejected be the algorithm steps defined in
Promise.anyReject Element Functions - LetlengthRejected be the number of non-optional parameters of the function definition in
Promise.anyReject Element Functions - LetonRejected be
CreateBuiltinFunction (stepsRejected,lengthRejected,"" , «[[AlreadyCalled]],[[Index]],[[Errors]],[[Capability]],[[RemainingElements]] »). - SetonRejected.[[AlreadyCalled]] to
false . - SetonRejected.[[Index]] toindex.
- SetonRejected.[[Errors]] toerrors.
- SetonRejected.[[Capability]] toresultCapability.
- SetonRejected.[[RemainingElements]] toremainingElementsCount.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] + 1.
- Perform ?
Invoke (nextPromise,"then" , «resultCapability.[[Resolve]],onRejected »). - Setindex toindex + 1.
- Letnext be ?
27.2.4.3.2Promise.any Reject Element Functions
APromise.any reject element function is an anonymous built-in function that is used to reject a specificPromise.any element. EachPromise.any reject element function has[[Index]],[[Errors]],[[Capability]],[[RemainingElements]], and[[AlreadyCalled]] internal slots.
When aPromise.any reject element function is called with argumentx, the following steps are taken:
- LetF be the
active function object . - IfF.[[AlreadyCalled]] is
true , returnundefined . - SetF.[[AlreadyCalled]] to
true . - Letindex beF.[[Index]].
- Leterrors beF.[[Errors]].
- LetpromiseCapability beF.[[Capability]].
- LetremainingElementsCount beF.[[RemainingElements]].
- Seterrors[index] tox.
- SetremainingElementsCount.[[Value]] toremainingElementsCount.[[Value]] - 1.
- IfremainingElementsCount.[[Value]] = 0, then
- Leterror be a newly created
AggregateError object. - Perform !
DefinePropertyOrThrow (error,"errors" , PropertyDescriptor {[[Configurable]]:true ,[[Enumerable]]:false ,[[Writable]]:true ,[[Value]]:CreateArrayFromList (errors) }). - Return ?
Call (promiseCapability.[[Reject]],undefined , «error »).
- Leterror be a newly created
- Return
undefined .
ThePromise.any reject element function is
27.2.4.4 Promise.prototype
The initial value ofPromise.prototype is the
This property has the attributes {[[Writable]]:
27.2.4.5 Promise.race (iterable )
This function returns a new promise which is settled in the same way as the first passed promise to settle. It resolves all elements of the passediterable to promises as it runs this algorithm.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - LetpromiseResolve be
Completion (GetPromiseResolve (C)). IfAbruptRejectPromise (promiseResolve,promiseCapability).- LetiteratorRecord be
Completion (GetIterator (iterable,sync )). IfAbruptRejectPromise (iteratorRecord,promiseCapability).- Letresult be
Completion (PerformPromiseRace (iteratorRecord,C,promiseCapability,promiseResolve)). - Ifresult is an
abrupt completion , then- IfiteratorRecord.[[Done]] is
false , setresult toCompletion (IteratorClose (iteratorRecord,result)). IfAbruptRejectPromise (result,promiseCapability).
- IfiteratorRecord.[[Done]] is
- Return ? result.
If theiterable argument yields no values or if none of the promises yielded byiterable ever settle, then the pending promise returned by this method will never be settled.
This function expects itsresolve method.
27.2.4.5.1 PerformPromiseRace (iteratorRecord,constructor,resultCapability,promiseResolve )
The abstract operation PerformPromiseRace takes argumentsiteratorRecord (an
- Repeat,
- Letnext be ?
IteratorStepValue (iteratorRecord). - Ifnext is
done , then- ReturnresultCapability.[[Promise]].
- LetnextPromise be ?
Call (promiseResolve,constructor, «next »). - Perform ?
Invoke (nextPromise,"then" , «resultCapability.[[Resolve]],resultCapability.[[Reject]] »).
- Letnext be ?
27.2.4.6 Promise.reject (r )
This function returns a new promise rejected with the passed argument.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Reject]],undefined , «r »). - ReturnpromiseCapability.[[Promise]].
This function expects its
27.2.4.7 Promise.resolve (x )
This function returns either a new promise resolved with the passed argument, or the argument itself if the argument is a promise produced by this
- LetC be the
this value. - IfC
is not an Object , throw aTypeError exception. - Return ?
PromiseResolve (C,x).
This function expects its
27.2.4.7.1 PromiseResolve (C,x )
The abstract operation PromiseResolve takes argumentsC (a
- If
IsPromise (x) istrue , then - LetpromiseCapability be ?
NewPromiseCapability (C). - Perform ?
Call (promiseCapability.[[Resolve]],undefined , «x »). - ReturnpromiseCapability.[[Promise]].
27.2.4.8 Promise.withResolvers ( )
This function returns an object with three properties: a new promise together with theresolve andreject functions associated with it.
- LetC be the
this value. - LetpromiseCapability be ?
NewPromiseCapability (C). - Letobj be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (obj,"promise" ,promiseCapability.[[Promise]]). - Perform !
CreateDataPropertyOrThrow (obj,"resolve" ,promiseCapability.[[Resolve]]). - Perform !
CreateDataPropertyOrThrow (obj,"reject" ,promiseCapability.[[Reject]]). - Returnobj.
27.2.4.9 get Promise [ @@species ]
Promise[@@species] is an
- Return the
this value.
The value of the
Promise prototype methods normally use their
27.2.5 Properties of the Promise Prototype Object
ThePromise prototype object:
- is%Promise.prototype%.
- has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is an
ordinary object . - does not have a[[PromiseState]] internal slot or any of the other internal slots of Promise instances.
27.2.5.1 Promise.prototype.catch (onRejected )
This method performs the following steps when called:
- Letpromise be the
this value. - Return ?
Invoke (promise,"then" , «undefined ,onRejected »).
27.2.5.2 Promise.prototype.constructor
The initial value ofPromise.prototype.constructor is
27.2.5.3 Promise.prototype.finally (onFinally )
This method performs the following steps when called:
- Letpromise be the
this value. - Ifpromise
is not an Object , throw aTypeError exception. - LetC be ?
SpeciesConstructor (promise,%Promise% ). Assert :IsConstructor (C) istrue .- If
IsCallable (onFinally) isfalse , then- LetthenFinally beonFinally.
- LetcatchFinally beonFinally.
- Else,
- LetthenFinallyClosure be a new
Abstract Closure with parameters (value) that capturesonFinally andC and performs the following steps when called:- Letresult be ?
Call (onFinally,undefined ). - Letp be ?
PromiseResolve (C,result). - LetreturnValue be a new
Abstract Closure with no parameters that capturesvalue and performs the following steps when called:- Returnvalue.
- LetvalueThunk be
CreateBuiltinFunction (returnValue, 0,"" , « »). - Return ?
Invoke (p,"then" , «valueThunk »).
- Letresult be ?
- LetthenFinally be
CreateBuiltinFunction (thenFinallyClosure, 1,"" , « »). - LetcatchFinallyClosure be a new
Abstract Closure with parameters (reason) that capturesonFinally andC and performs the following steps when called:- Letresult be ?
Call (onFinally,undefined ). - Letp be ?
PromiseResolve (C,result). - LetthrowReason be a new
Abstract Closure with no parameters that capturesreason and performs the following steps when called:- Return
ThrowCompletion (reason).
- Return
- Letthrower be
CreateBuiltinFunction (throwReason, 0,"" , « »). - Return ?
Invoke (p,"then" , «thrower »).
- Letresult be ?
- LetcatchFinally be
CreateBuiltinFunction (catchFinallyClosure, 1,"" , « »).
- LetthenFinallyClosure be a new
- Return ?
Invoke (promise,"then" , «thenFinally,catchFinally »).
27.2.5.4 Promise.prototype.then (onFulfilled,onRejected )
This method performs the following steps when called:
- Letpromise be the
this value. - If
IsPromise (promise) isfalse , throw aTypeError exception. - LetC be ?
SpeciesConstructor (promise,%Promise% ). - LetresultCapability be ?
NewPromiseCapability (C). - Return
PerformPromiseThen (promise,onFulfilled,onRejected,resultCapability).
27.2.5.4.1 PerformPromiseThen (promise,onFulfilled,onRejected [ ,resultCapability ] )
The abstract operation PerformPromiseThen takes argumentspromise (a Promise),onFulfilled (an
Assert :IsPromise (promise) istrue .- IfresultCapability is not present, then
- SetresultCapability to
undefined .
- SetresultCapability to
- If
IsCallable (onFulfilled) isfalse , then- LetonFulfilledJobCallback be
empty .
- LetonFulfilledJobCallback be
- Else,
- LetonFulfilledJobCallback be
HostMakeJobCallback (onFulfilled).
- LetonFulfilledJobCallback be
- If
IsCallable (onRejected) isfalse , then- LetonRejectedJobCallback be
empty .
- LetonRejectedJobCallback be
- Else,
- LetonRejectedJobCallback be
HostMakeJobCallback (onRejected).
- LetonRejectedJobCallback be
- LetfulfillReaction be the
PromiseReaction Record {[[Capability]]:resultCapability,[[Type]]:fulfill ,[[Handler]]:onFulfilledJobCallback }. - LetrejectReaction be the
PromiseReaction Record {[[Capability]]:resultCapability,[[Type]]:reject ,[[Handler]]:onRejectedJobCallback }. - Ifpromise.[[PromiseState]] is
pending , then- AppendfulfillReaction topromise.[[PromiseFulfillReactions]].
- AppendrejectReaction topromise.[[PromiseRejectReactions]].
- Else ifpromise.[[PromiseState]] is
fulfilled , then- Letvalue bepromise.[[PromiseResult]].
- LetfulfillJob be
NewPromiseReactionJob (fulfillReaction,value). - Perform
HostEnqueuePromiseJob (fulfillJob.[[Job]],fulfillJob.[[Realm]]).
- Else,
Assert : The value ofpromise.[[PromiseState]] isrejected .- Letreason bepromise.[[PromiseResult]].
- Ifpromise.[[PromiseIsHandled]] is
false , performHostPromiseRejectionTracker (promise,"handle" ). - LetrejectJob be
NewPromiseReactionJob (rejectReaction,reason). - Perform
HostEnqueuePromiseJob (rejectJob.[[Job]],rejectJob.[[Realm]]).
- Setpromise.[[PromiseIsHandled]] to
true . - IfresultCapability is
undefined , then- Return
undefined .
- Return
- Else,
- ReturnresultCapability.[[Promise]].
27.2.5.5 Promise.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.2.6 Properties of Promise Instances
Promise instances are
| Internal Slot | Type | Description |
|---|---|---|
| [[PromiseState]] | Governs how a promise will react to incoming calls to itsthen method. | |
| [[PromiseResult]] | an | The value with which the promise has been fulfilled or rejected, if any. Only meaningful if[[PromiseState]] is not |
| [[PromiseFulfillReactions]] | a | |
| [[PromiseRejectReactions]] | a | |
| [[PromiseIsHandled]] | a Boolean | Indicates whether the promise has ever had a fulfillment or rejection handler; used in unhandled rejection tracking. |
27.3 GeneratorFunction Objects
GeneratorFunctions are functions that are usually created by evaluating
27.3.1 The GeneratorFunction Constructor
The GeneratorFunction
- is%GeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new GeneratorFunction when called as a function rather than as a
constructor . Thus the function callGeneratorFunction (…)is equivalent to the object creation expressionnew GeneratorFunction (…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified GeneratorFunction behaviour must include asupercall to the GeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in GeneratorFunction behaviour. All ECMAScript syntactic forms for defining generatorfunction objects create direct instances of GeneratorFunction. There is no syntactic means to create instances of GeneratorFunction subclasses.
27.3.1.1 GeneratorFunction ( ...parameterArgs,bodyArg )
The last argument (if any) specifies the body (executable code) of a generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- LetC be the
active function object . - IfbodyArg is not present, setbodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,generator ,parameterArgs,bodyArg).
See NOTE for
27.3.2 Properties of the GeneratorFunction Constructor
The GeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a[[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"GeneratorFunction" . - has the following properties:
27.3.2.1 GeneratorFunction.prototype
The initial value ofGeneratorFunction.prototype is the
This property has the attributes {[[Writable]]:
27.3.3 Properties of the GeneratorFunction Prototype Object
TheGeneratorFunction prototype object:
- is%GeneratorFunction.prototype% (see
Figure 6 ). - is an
ordinary object . - is not a
function object and does not have an[[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 88 . - has a[[Prototype]] internal slot whose value is
%Function.prototype% .
27.3.3.1 GeneratorFunction.prototype.constructor
The initial value ofGeneratorFunction.prototype.constructor is
This property has the attributes {[[Writable]]:
27.3.3.2 GeneratorFunction.prototype.prototype
The initial value ofGeneratorFunction.prototype.prototype is the
This property has the attributes {[[Writable]]:
27.3.3.3 GeneratorFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.3.4 GeneratorFunction Instances
Every GeneratorFunction instance is an ECMAScript
Each GeneratorFunction instance has the following own properties:
27.3.4.1 length
The specification for the
27.3.4.2 name
The specification for the
27.3.4.3 prototype
Whenever a GeneratorFunction instance is created another
This property has the attributes {[[Writable]]:
Unlike Function instances, the object that is the value of a GeneratorFunction's
27.4 AsyncGeneratorFunction Objects
AsyncGeneratorFunctions are functions that are usually created by evaluating
27.4.1 The AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is%AsyncGeneratorFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncGeneratorFunction when called as a function rather than as a
constructor . Thus the function callAsyncGeneratorFunction (...)is equivalent to the object creation expressionnew AsyncGeneratorFunction (...)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncGeneratorFunction behaviour must include asupercall to the AsyncGeneratorFunctionconstructor to create and initialize subclass instances with the internal slots necessary for built-in AsyncGeneratorFunction behaviour. All ECMAScript syntactic forms for defining async generatorfunction objects create direct instances of AsyncGeneratorFunction. There is no syntactic means to create instances of AsyncGeneratorFunction subclasses.
27.4.1.1 AsyncGeneratorFunction ( ...parameterArgs,bodyArg )
The last argument (if any) specifies the body (executable code) of an async generator function; any preceding arguments specify formal parameters.
This function performs the following steps when called:
- LetC be the
active function object . - IfbodyArg is not present, setbodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async-generator ,parameterArgs,bodyArg).
See NOTE for
27.4.2 Properties of the AsyncGeneratorFunction Constructor
The AsyncGeneratorFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a[[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncGeneratorFunction" . - has the following properties:
27.4.2.1 AsyncGeneratorFunction.prototype
The initial value ofAsyncGeneratorFunction.prototype is the
This property has the attributes {[[Writable]]:
27.4.3 Properties of the AsyncGeneratorFunction Prototype Object
TheAsyncGeneratorFunction prototype object:
- is%AsyncGeneratorFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an[[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 orTable 89 . - has a[[Prototype]] internal slot whose value is
%Function.prototype% .
27.4.3.1 AsyncGeneratorFunction.prototype.constructor
The initial value ofAsyncGeneratorFunction.prototype.constructor is
This property has the attributes {[[Writable]]:
27.4.3.2 AsyncGeneratorFunction.prototype.prototype
The initial value ofAsyncGeneratorFunction.prototype.prototype is the
This property has the attributes {[[Writable]]:
27.4.3.3 AsyncGeneratorFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.4.4 AsyncGeneratorFunction Instances
Every AsyncGeneratorFunction instance is an ECMAScript
Each AsyncGeneratorFunction instance has the following own properties:
27.4.4.1 length
The value of the
This property has the attributes {[[Writable]]:
27.4.4.2 name
The specification for the
27.4.4.3 prototype
Whenever an AsyncGeneratorFunction instance is created, another
This property has the attributes {[[Writable]]:
Unlike function instances, the object that is the value of an AsyncGeneratorFunction's
27.5 Generator Objects
A Generator is an instance of a generator function and conforms to both theIterator andIterable interfaces.
Generator instances directly inherit properties from the object that is the initial value of the
27.5.1 Properties of the Generator Prototype Object
TheGenerator prototype object:
- is%GeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not a Generator instance and does not have a[[GeneratorState]] internal slot.
- has a[[Prototype]] internal slot whose value is
%IteratorPrototype% . - has properties that are indirectly inherited by all Generator instances.
27.5.1.1 Generator.prototype.constructor
The initial value ofGenerator.prototype.constructor is
This property has the attributes {[[Writable]]:
27.5.1.2 Generator.prototype.next (value )
- Return ?
GeneratorResume (this value,value,empty ).
27.5.1.3 Generator.prototype.return (value )
This method performs the following steps when called:
- Letg be the
this value. - LetC be
Completion Record {[[Type]]:return ,[[Value]]:value,[[Target]]:empty }. - Return ?
GeneratorResumeAbrupt (g,C,empty ).
27.5.1.4 Generator.prototype.throw (exception )
This method performs the following steps when called:
- Letg be the
this value. - LetC be
ThrowCompletion (exception). - Return ?
GeneratorResumeAbrupt (g,C,empty ).
27.5.1.5 Generator.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.5.2 Properties of Generator Instances
Generator instances are initially created with the internal slots described in
| Internal Slot | Type | Description |
|---|---|---|
| [[GeneratorState]] | The current execution state of the generator. | |
| [[GeneratorContext]] | an | The |
| [[GeneratorBrand]] | a String or | A brand used to distinguish different kinds of generators. The[[GeneratorBrand]] of generators declared by |
27.5.3 Generator Abstract Operations
27.5.3.1 GeneratorStart (generator,generatorBody )
The abstract operation GeneratorStart takes argumentsgenerator (a Generator) andgeneratorBody (a
Assert : The value ofgenerator.[[GeneratorState]] isundefined .- LetgenContext be the
running execution context . - Set the Generator component ofgenContext togenerator.
- Letclosure be a new
Abstract Closure with no parameters that capturesgeneratorBody and performs the following steps when called:- LetacGenContext be the
running execution context . - LetacGenerator be the Generator component ofacGenContext.
- IfgeneratorBody is a
Parse Node , then- Letresult be
Completion (Evaluation ofgeneratorBody).
- Letresult be
- Else,
Assert :generatorBody is anAbstract Closure with no parameters.- Letresult begeneratorBody().
Assert : If we return here, the generator either threw an exception or performed either an implicit or explicit return.- RemoveacGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - SetacGenerator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated withacGenerator can be discarded at this point. - Ifresult is a
normal completion , then- LetresultValue be
undefined .
- LetresultValue be
- Else ifresult is a
return completion , then- LetresultValue beresult.[[Value]].
- Else,
Assert :result is athrow completion .- Return ? result.
- Return
CreateIterResultObject (resultValue,true ).
- LetacGenContext be the
- Set the code evaluation state ofgenContext such that when evaluation is resumed for that
execution context ,closure will be called with no arguments. - Setgenerator.[[GeneratorContext]] togenContext.
- Setgenerator.[[GeneratorState]] to
suspended-start . - Return
unused .
27.5.3.2 GeneratorValidate (generator,generatorBrand )
The abstract operation GeneratorValidate takes argumentsgenerator (an
- Perform ?
RequireInternalSlot (generator,[[GeneratorState]]). - Perform ?
RequireInternalSlot (generator,[[GeneratorBrand]]). - Ifgenerator.[[GeneratorBrand]] is notgeneratorBrand, throw a
TypeError exception. Assert :generator also has a[[GeneratorContext]] internal slot.- Letstate begenerator.[[GeneratorState]].
- Ifstate is
executing , throw aTypeError exception. - Returnstate.
27.5.3.3 GeneratorResume (generator,value,generatorBrand )
The abstract operation GeneratorResume takes argumentsgenerator (an
- Letstate be ?
GeneratorValidate (generator,generatorBrand). - Ifstate is
completed , returnCreateIterResultObject (undefined ,true ). Assert :state is eithersuspended-start orsuspended-yield .- LetgenContext begenerator.[[GeneratorContext]].
- LetmethodContext be the
running execution context . - SuspendmethodContext.
- Setgenerator.[[GeneratorState]] to
executing . - PushgenContext onto the
execution context stack ;genContext is now therunning execution context . - Resume the suspended evaluation ofgenContext using
NormalCompletion (value) as the result of the operation that suspended it. Letresult be the value returned by the resumed computation. Assert : When we return here,genContext has already been removed from theexecution context stack andmethodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.4 GeneratorResumeAbrupt (generator,abruptCompletion,generatorBrand )
The abstract operation GeneratorResumeAbrupt takes argumentsgenerator (an
- Letstate be ?
GeneratorValidate (generator,generatorBrand). - Ifstate is
suspended-start , then- Setgenerator.[[GeneratorState]] to
completed . - NOTE: Once a generator enters the
completed state it never leaves it and its associatedexecution context is never resumed. Any execution state associated withgenerator can be discarded at this point. - Setstate to
completed .
- Setgenerator.[[GeneratorState]] to
- Ifstate is
completed , then- IfabruptCompletion is a
return completion , then- Return
CreateIterResultObject (abruptCompletion.[[Value]],true ).
- Return
- Return ? abruptCompletion.
- IfabruptCompletion is a
Assert :state issuspended-yield .- LetgenContext begenerator.[[GeneratorContext]].
- LetmethodContext be the
running execution context . - SuspendmethodContext.
- Setgenerator.[[GeneratorState]] to
executing . - PushgenContext onto the
execution context stack ;genContext is now therunning execution context . - Resume the suspended evaluation ofgenContext usingabruptCompletion as the result of the operation that suspended it. Letresult be the
Completion Record returned by the resumed computation. Assert : When we return here,genContext has already been removed from theexecution context stack andmethodContext is the currentlyrunning execution context .- Return ? result.
27.5.3.5 GetGeneratorKind ( )
The abstract operation GetGeneratorKind takes no arguments and returns
- LetgenContext be the
running execution context . - IfgenContext does not have a Generator component, return
non-generator . - Letgenerator be the Generator component ofgenContext.
- Ifgenerator has an[[AsyncGeneratorState]] internal slot, return
async . - Else, return
sync .
27.5.3.6 GeneratorYield (iterNextObj )
The abstract operation GeneratorYield takes argumentiterNextObj (an Object that conforms to theIteratorResult interface) and returns either a
- LetgenContext be the
running execution context . Assert :genContext is theexecution context of a generator.- Letgenerator be the value of the Generator component ofgenContext.
Assert :GetGeneratorKind () issync .- Setgenerator.[[GeneratorState]] to
suspended-yield . - RemovegenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - LetcallerContext be the
running execution context . - ResumecallerContext passing
NormalCompletion (iterNextObj). IfgenContext is ever resumed again, letresumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, thengenContext is therunning execution context again.- ReturnresumptionValue.
27.5.3.7 Yield (value )
The abstract operation Yield takes argumentvalue (an
- LetgeneratorKind be
GetGeneratorKind (). - IfgeneratorKind is
async , return ?AsyncGeneratorYield (?Await (value)). - Otherwise, return ?
GeneratorYield (CreateIterResultObject (value,false )).
27.5.3.8 CreateIteratorFromClosure (closure,generatorBrand,generatorPrototype )
The abstract operation CreateIteratorFromClosure takes argumentsclosure (an
- NOTE:closure can contain uses of the
Yield operation to yield an IteratorResult object. - LetinternalSlotsList be «[[GeneratorState]],[[GeneratorContext]],[[GeneratorBrand]] ».
- Letgenerator be
OrdinaryObjectCreate (generatorPrototype,internalSlotsList). - Setgenerator.[[GeneratorBrand]] togeneratorBrand.
- Setgenerator.[[GeneratorState]] to
undefined . - LetcallerContext be the
running execution context . - LetcalleeContext be a new
execution context . - Set the Function ofcalleeContext to
null . - Set the
Realm ofcalleeContext tothe current Realm Record . - Set the ScriptOrModule ofcalleeContext tocallerContext's ScriptOrModule.
- IfcallerContext is not already suspended, suspendcallerContext.
- PushcalleeContext onto the
execution context stack ;calleeContext is now therunning execution context . - Perform
GeneratorStart (generator,closure). - RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Returngenerator.
27.6 AsyncGenerator Objects
An AsyncGenerator is an instance of an async generator function and conforms to both the AsyncIterator and AsyncIterable interfaces.
AsyncGenerator instances directly inherit properties from the object that is the initial value of the
27.6.1 Properties of the AsyncGenerator Prototype Object
TheAsyncGenerator prototype object:
- is%AsyncGeneratorFunction.prototype.prototype%.
- is an
ordinary object . - is not an AsyncGenerator instance and does not have an[[AsyncGeneratorState]] internal slot.
- has a[[Prototype]] internal slot whose value is
%AsyncIteratorPrototype% . - has properties that are indirectly inherited by all AsyncGenerator instances.
27.6.1.1 AsyncGenerator.prototype.constructor
The initial value ofAsyncGenerator.prototype.constructor is
This property has the attributes {[[Writable]]:
27.6.1.2 AsyncGenerator.prototype.next (value )
- Letgenerator be the
this value. - LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - Letresult be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result,promiseCapability).- Letstate begenerator.[[AsyncGeneratorState]].
- Ifstate is
completed , then- LetiteratorResult be
CreateIterResultObject (undefined ,true ). - Perform !
Call (promiseCapability.[[Resolve]],undefined , «iteratorResult »). - ReturnpromiseCapability.[[Promise]].
- LetiteratorResult be
- Letcompletion be
NormalCompletion (value). - Perform
AsyncGeneratorEnqueue (generator,completion,promiseCapability). - Ifstate is either
suspended-start orsuspended-yield , then- Perform
AsyncGeneratorResume (generator,completion).
- Perform
- Else,
Assert :state is eitherexecuting orawaiting-return .
- ReturnpromiseCapability.[[Promise]].
27.6.1.3 AsyncGenerator.prototype.return (value )
- Letgenerator be the
this value. - LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - Letresult be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result,promiseCapability).- Letcompletion be
Completion Record {[[Type]]:return ,[[Value]]:value,[[Target]]:empty }. - Perform
AsyncGeneratorEnqueue (generator,completion,promiseCapability). - Letstate begenerator.[[AsyncGeneratorState]].
- Ifstate is either
suspended-start orcompleted , then- Setgenerator.[[AsyncGeneratorState]] to
awaiting-return . - Perform !
AsyncGeneratorAwaitReturn (generator).
- Setgenerator.[[AsyncGeneratorState]] to
- Else ifstate is
suspended-yield , then- Perform
AsyncGeneratorResume (generator,completion).
- Perform
- Else,
Assert :state is eitherexecuting orawaiting-return .
- ReturnpromiseCapability.[[Promise]].
27.6.1.4 AsyncGenerator.prototype.throw (exception )
- Letgenerator be the
this value. - LetpromiseCapability be !
NewPromiseCapability (%Promise% ). - Letresult be
Completion (AsyncGeneratorValidate (generator,empty )). IfAbruptRejectPromise (result,promiseCapability).- Letstate begenerator.[[AsyncGeneratorState]].
- Ifstate is
suspended-start , then- Setgenerator.[[AsyncGeneratorState]] to
completed . - Setstate to
completed .
- Setgenerator.[[AsyncGeneratorState]] to
- Ifstate is
completed , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «exception »). - ReturnpromiseCapability.[[Promise]].
- Perform !
- Letcompletion be
ThrowCompletion (exception). - Perform
AsyncGeneratorEnqueue (generator,completion,promiseCapability). - Ifstate is
suspended-yield , then- Perform
AsyncGeneratorResume (generator,completion).
- Perform
- Else,
Assert :state is eitherexecuting orawaiting-return .
- ReturnpromiseCapability.[[Promise]].
27.6.1.5 AsyncGenerator.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.6.2 Properties of AsyncGenerator Instances
AsyncGenerator instances are initially created with the internal slots described below:
| Internal Slot | Type | Description |
|---|---|---|
| [[AsyncGeneratorState]] | The current execution state of the async generator. | |
| [[AsyncGeneratorContext]] | an | The |
| [[AsyncGeneratorQueue]] | a | |
| [[GeneratorBrand]] | a String or | A brand used to distinguish different kinds of async generators. The[[GeneratorBrand]] of async generators declared by |
27.6.3 AsyncGenerator Abstract Operations
27.6.3.1 AsyncGeneratorRequest Records
AnAsyncGeneratorRequest is a
They have the following fields:
| Field Name | Value | Meaning |
|---|---|---|
| [[Completion]] | a | The |
| [[Capability]] | a | The promise capabilities associated with this request. |
27.6.3.2 AsyncGeneratorStart (generator,generatorBody )
The abstract operation AsyncGeneratorStart takes argumentsgenerator (an AsyncGenerator) andgeneratorBody (a
Assert :generator.[[AsyncGeneratorState]] isundefined .- LetgenContext be the
running execution context . - Set the Generator component ofgenContext togenerator.
- Letclosure be a new
Abstract Closure with no parameters that capturesgeneratorBody and performs the following steps when called:- LetacGenContext be the
running execution context . - LetacGenerator be the Generator component ofacGenContext.
- IfgeneratorBody is a
Parse Node , then- Letresult be
Completion (Evaluation ofgeneratorBody).
- Letresult be
- Else,
Assert :generatorBody is anAbstract Closure with no parameters.- Letresult be
Completion (generatorBody()).
Assert : If we return here, the async generator either threw an exception or performed either an implicit or explicit return.- RemoveacGenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - SetacGenerator.[[AsyncGeneratorState]] to
completed . - Ifresult is a
normal completion , setresult toNormalCompletion (undefined ). - Ifresult is a
return completion , setresult toNormalCompletion (result.[[Value]]). - Perform
AsyncGeneratorCompleteStep (acGenerator,result,true ). - Perform
AsyncGeneratorDrainQueue (acGenerator). - Return
undefined .
- LetacGenContext be the
- Set the code evaluation state ofgenContext such that when evaluation is resumed for that
execution context ,closure will be called with no arguments. - Setgenerator.[[AsyncGeneratorContext]] togenContext.
- Setgenerator.[[AsyncGeneratorState]] to
suspended-start . - Setgenerator.[[AsyncGeneratorQueue]] to a new empty
List . - Return
unused .
27.6.3.3 AsyncGeneratorValidate (generator,generatorBrand )
The abstract operation AsyncGeneratorValidate takes argumentsgenerator (an
- Perform ?
RequireInternalSlot (generator,[[AsyncGeneratorContext]]). - Perform ?
RequireInternalSlot (generator,[[AsyncGeneratorState]]). - Perform ?
RequireInternalSlot (generator,[[AsyncGeneratorQueue]]). - Ifgenerator.[[GeneratorBrand]] is notgeneratorBrand, throw a
TypeError exception. - Return
unused .
27.6.3.4 AsyncGeneratorEnqueue (generator,completion,promiseCapability )
The abstract operation AsyncGeneratorEnqueue takes argumentsgenerator (an AsyncGenerator),completion (a
- Letrequest be
AsyncGeneratorRequest {[[Completion]]:completion,[[Capability]]:promiseCapability }. - Appendrequest togenerator.[[AsyncGeneratorQueue]].
- Return
unused .
27.6.3.5 AsyncGeneratorCompleteStep (generator,completion,done [ ,realm ] )
The abstract operation AsyncGeneratorCompleteStep takes argumentsgenerator (an AsyncGenerator),completion (a
Assert :generator.[[AsyncGeneratorQueue]] is not empty.- Letnext be the first element ofgenerator.[[AsyncGeneratorQueue]].
- Remove the first element fromgenerator.[[AsyncGeneratorQueue]].
- LetpromiseCapability benext.[[Capability]].
- Letvalue becompletion.[[Value]].
- Ifcompletion is a
throw completion , then- Perform !
Call (promiseCapability.[[Reject]],undefined , «value »).
- Perform !
- Else,
Assert :completion is anormal completion .- Ifrealm is present, then
- LetoldRealm be the
running execution context 'sRealm . - Set the
running execution context 'sRealm torealm. - LetiteratorResult be
CreateIterResultObject (value,done). - Set the
running execution context 'sRealm tooldRealm.
- LetoldRealm be the
- Else,
- LetiteratorResult be
CreateIterResultObject (value,done).
- LetiteratorResult be
- Perform !
Call (promiseCapability.[[Resolve]],undefined , «iteratorResult »).
- Return
unused .
27.6.3.6 AsyncGeneratorResume (generator,completion )
The abstract operation AsyncGeneratorResume takes argumentsgenerator (an AsyncGenerator) andcompletion (a
Assert :generator.[[AsyncGeneratorState]] is eithersuspended-start orsuspended-yield .- LetgenContext begenerator.[[AsyncGeneratorContext]].
- LetcallerContext be the
running execution context . - SuspendcallerContext.
- Setgenerator.[[AsyncGeneratorState]] to
executing . - PushgenContext onto the
execution context stack ;genContext is now therunning execution context . - Resume the suspended evaluation ofgenContext usingcompletion as the result of the operation that suspended it. Letresult be the
Completion Record returned by the resumed computation. Assert :result is never anabrupt completion .Assert : When we return here,genContext has already been removed from theexecution context stack andcallerContext is the currentlyrunning execution context .- Return
unused .
27.6.3.7 AsyncGeneratorUnwrapYieldResumption (resumptionValue )
The abstract operation AsyncGeneratorUnwrapYieldResumption takes argumentresumptionValue (a
- IfresumptionValue is not a
return completion , return ? resumptionValue. - Letawaited be
Completion (Await (resumptionValue.[[Value]])). - Ifawaited is a
throw completion , return ? awaited. Assert :awaited is anormal completion .- Return
Completion Record {[[Type]]:return ,[[Value]]:awaited.[[Value]],[[Target]]:empty }.
27.6.3.8 AsyncGeneratorYield (value )
The abstract operation AsyncGeneratorYield takes argumentvalue (an
- LetgenContext be the
running execution context . Assert :genContext is theexecution context of a generator.- Letgenerator be the value of the Generator component ofgenContext.
Assert :GetGeneratorKind () isasync .- Letcompletion be
NormalCompletion (value). Assert : Theexecution context stack has at least two elements.- LetpreviousContext be the second to top element of the
execution context stack . - LetpreviousRealm bepreviousContext's
Realm . - Perform
AsyncGeneratorCompleteStep (generator,completion,false ,previousRealm). - Letqueue begenerator.[[AsyncGeneratorQueue]].
- Ifqueue is not empty, then
- NOTE: Execution continues without suspending the generator.
- LettoYield be the first element ofqueue.
- LetresumptionValue be
Completion (toYield.[[Completion]]). - Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Else,
- Setgenerator.[[AsyncGeneratorState]] to
suspended-yield . - RemovegenContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - LetcallerContext be the
running execution context . - ResumecallerContext passing
undefined . IfgenContext is ever resumed again, letresumptionValue be theCompletion Record with which it is resumed. Assert : If control reaches here, thengenContext is therunning execution context again.- Return ?
AsyncGeneratorUnwrapYieldResumption (resumptionValue).
- Setgenerator.[[AsyncGeneratorState]] to
27.6.3.9 AsyncGeneratorAwaitReturn (generator )
The abstract operation AsyncGeneratorAwaitReturn takes argumentgenerator (an AsyncGenerator) and returns either a
- Letqueue begenerator.[[AsyncGeneratorQueue]].
Assert :queue is not empty.- Letnext be the first element ofqueue.
- Letcompletion be
Completion (next.[[Completion]]). Assert :completion is areturn completion .- Letpromise be ?
PromiseResolve (%Promise% ,completion.[[Value]]). - LetfulfilledClosure be a new
Abstract Closure with parameters (value) that capturesgenerator and performs the following steps when called:- Setgenerator.[[AsyncGeneratorState]] to
completed . - Letresult be
NormalCompletion (value). - Perform
AsyncGeneratorCompleteStep (generator,result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
undefined .
- Setgenerator.[[AsyncGeneratorState]] to
- LetonFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - LetrejectedClosure be a new
Abstract Closure with parameters (reason) that capturesgenerator and performs the following steps when called:- Setgenerator.[[AsyncGeneratorState]] to
completed . - Letresult be
ThrowCompletion (reason). - Perform
AsyncGeneratorCompleteStep (generator,result,true ). - Perform
AsyncGeneratorDrainQueue (generator). - Return
undefined .
- Setgenerator.[[AsyncGeneratorState]] to
- LetonRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise,onFulfilled,onRejected). - Return
unused .
27.6.3.10 AsyncGeneratorDrainQueue (generator )
The abstract operation AsyncGeneratorDrainQueue takes argumentgenerator (an AsyncGenerator) and returns
Assert :generator.[[AsyncGeneratorState]] iscompleted .- Letqueue begenerator.[[AsyncGeneratorQueue]].
- Ifqueue is empty, return
unused . - Letdone be
false . - Repeat, whiledone is
false ,- Letnext be the first element ofqueue.
- Letcompletion be
Completion (next.[[Completion]]). - Ifcompletion is a
return completion , then- Setgenerator.[[AsyncGeneratorState]] to
awaiting-return . - Perform !
AsyncGeneratorAwaitReturn (generator). - Setdone to
true .
- Setgenerator.[[AsyncGeneratorState]] to
- Else,
- Ifcompletion is a
normal completion , then- Setcompletion to
NormalCompletion (undefined ).
- Setcompletion to
- Perform
AsyncGeneratorCompleteStep (generator,completion,true ). - Ifqueue is empty, setdone to
true .
- Ifcompletion is a
- Return
unused .
27.6.3.11 CreateAsyncIteratorFromClosure (closure,generatorBrand,generatorPrototype )
The abstract operation CreateAsyncIteratorFromClosure takes argumentsclosure (an
- NOTE:closure can contain uses of the
Await operation and uses of theYield operation to yield an IteratorResult object. - LetinternalSlotsList be «[[AsyncGeneratorState]],[[AsyncGeneratorContext]],[[AsyncGeneratorQueue]],[[GeneratorBrand]] ».
- Letgenerator be
OrdinaryObjectCreate (generatorPrototype,internalSlotsList). - Setgenerator.[[GeneratorBrand]] togeneratorBrand.
- Setgenerator.[[AsyncGeneratorState]] to
undefined . - LetcallerContext be the
running execution context . - LetcalleeContext be a new
execution context . - Set the Function ofcalleeContext to
null . - Set the
Realm ofcalleeContext tothe current Realm Record . - Set the ScriptOrModule ofcalleeContext tocallerContext's ScriptOrModule.
- IfcallerContext is not already suspended, suspendcallerContext.
- PushcalleeContext onto the
execution context stack ;calleeContext is now therunning execution context . - Perform
AsyncGeneratorStart (generator,closure). - RemovecalleeContext from the
execution context stack and restorecallerContext as therunning execution context . - Returngenerator.
27.7 AsyncFunction Objects
AsyncFunctions are functions that are usually created by evaluating
27.7.1 The AsyncFunction Constructor
The AsyncFunction
- is%AsyncFunction%.
- is a subclass of
Function. - creates and initializes a new AsyncFunction when called as a function rather than as a
constructor . Thus the function callAsyncFunction(…)is equivalent to the object creation expressionnew AsyncFunction(…)with the same arguments. - may be used as the value of an
extendsclause of a class definition. Subclassconstructors that intend to inherit the specified AsyncFunction behaviour must include asupercall to the AsyncFunctionconstructor to create and initialize a subclass instance with the internal slots necessary for built-in async function behaviour. All ECMAScript syntactic forms for defining asyncfunction objects create direct instances of AsyncFunction. There is no syntactic means to create instances of AsyncFunction subclasses.
27.7.1.1 AsyncFunction ( ...parameterArgs,bodyArg )
The last argument (if any) specifies the body (executable code) of an async function. Any preceding arguments specify formal parameters.
This function performs the following steps when called:
- LetC be the
active function object . - IfbodyArg is not present, setbodyArg to the empty String.
- Return ?
CreateDynamicFunction (C, NewTarget,async ,parameterArgs,bodyArg).
27.7.2 Properties of the AsyncFunction Constructor
The AsyncFunction
- is a standard built-in
function object that inherits from the Functionconstructor . - has a[[Prototype]] internal slot whose value is
%Function% . - has a
"length" property whose value is1 𝔽. - has a
"name" property whose value is"AsyncFunction" . - has the following properties:
27.7.2.1 AsyncFunction.prototype
The initial value ofAsyncFunction.prototype is the
This property has the attributes {[[Writable]]:
27.7.3 Properties of the AsyncFunction Prototype Object
TheAsyncFunction prototype object:
- is%AsyncFunction.prototype%.
- is an
ordinary object . - is not a
function object and does not have an[[ECMAScriptCode]] internal slot or any other of the internal slots listed inTable 30 . - has a[[Prototype]] internal slot whose value is
%Function.prototype% .
27.7.3.1 AsyncFunction.prototype.constructor
The initial value ofAsyncFunction.prototype.constructor is
This property has the attributes {[[Writable]]:
27.7.3.2 AsyncFunction.prototype [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
27.7.4 AsyncFunction Instances
Every AsyncFunction instance is an ECMAScript
Each AsyncFunction instance has the following own properties:
27.7.4.1 length
The specification for the
27.7.4.2 name
The specification for the
27.7.5 Async Functions Abstract Operations
27.7.5.1 AsyncFunctionStart (promiseCapability,asyncFunctionBody )
The abstract operation AsyncFunctionStart takes argumentspromiseCapability (a
- LetrunningContext be the
running execution context . - LetasyncContext be a copy ofrunningContext.
- NOTE: Copying the execution state is required for
AsyncBlockStart to resume its execution. It is ill-defined to resume a currently executing context. - Perform
AsyncBlockStart (promiseCapability,asyncFunctionBody,asyncContext). - Return
unused .
27.7.5.2 AsyncBlockStart (promiseCapability,asyncBody,asyncContext )
The abstract operation AsyncBlockStart takes argumentspromiseCapability (a
Assert :promiseCapability is aPromiseCapability Record .- LetrunningContext be the
running execution context . - Letclosure be a new
Abstract Closure with no parameters that capturespromiseCapability andasyncBody and performs the following steps when called:- LetacAsyncContext be the
running execution context . - Letresult be
Completion (Evaluation ofasyncBody). Assert : If we return here, the async function either threw an exception or performed an implicit or explicit return; all awaiting is done.- RemoveacAsyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - Ifresult is a
normal completion , then- Perform !
Call (promiseCapability.[[Resolve]],undefined , «undefined »).
- Perform !
- Else ifresult is a
return completion , then- Perform !
Call (promiseCapability.[[Resolve]],undefined , «result.[[Value]] »).
- Perform !
- Else,
Assert :result is athrow completion .- Perform !
Call (promiseCapability.[[Reject]],undefined , «result.[[Value]] »).
- Return
unused .
- LetacAsyncContext be the
- Set the code evaluation state ofasyncContext such that when evaluation is resumed for that
execution context ,closure will be called with no arguments. - PushasyncContext onto the
execution context stack ;asyncContext is now therunning execution context . - Resume the suspended evaluation ofasyncContext. Letresult be the value returned by the resumed computation.
Assert : When we return here,asyncContext has already been removed from theexecution context stack andrunningContext is the currentlyrunning execution context .Assert :result is anormal completion with a value ofunused . The possible sources of this value areAwait or, if the async function doesn't await anything, step3.h above.- Return
unused .
27.7.5.3 Await (value )
The abstract operation Await takes argumentvalue (an
- LetasyncContext be the
running execution context . - Letpromise be ?
PromiseResolve (%Promise% ,value). - LetfulfilledClosure be a new
Abstract Closure with parameters (v) that capturesasyncContext and performs the following steps when called:- LetprevContext be the
running execution context . - SuspendprevContext.
- PushasyncContext onto the
execution context stack ;asyncContext is now therunning execution context . - Resume the suspended evaluation ofasyncContext using
NormalCompletion (v) as the result of the operation that suspended it. Assert : When we reach this step,asyncContext has already been removed from theexecution context stack andprevContext is the currentlyrunning execution context .- Return
undefined .
- LetprevContext be the
- LetonFulfilled be
CreateBuiltinFunction (fulfilledClosure, 1,"" , « »). - LetrejectedClosure be a new
Abstract Closure with parameters (reason) that capturesasyncContext and performs the following steps when called:- LetprevContext be the
running execution context . - SuspendprevContext.
- PushasyncContext onto the
execution context stack ;asyncContext is now therunning execution context . - Resume the suspended evaluation ofasyncContext using
ThrowCompletion (reason) as the result of the operation that suspended it. Assert : When we reach this step,asyncContext has already been removed from theexecution context stack andprevContext is the currentlyrunning execution context .- Return
undefined .
- LetprevContext be the
- LetonRejected be
CreateBuiltinFunction (rejectedClosure, 1,"" , « »). - Perform
PerformPromiseThen (promise,onFulfilled,onRejected). - RemoveasyncContext from the
execution context stack and restore theexecution context that is at the top of theexecution context stack as therunning execution context . - LetcallerContext be the
running execution context . - ResumecallerContext passing
empty . IfasyncContext is ever resumed again, letcompletion be theCompletion Record with which it is resumed. Assert : If control reaches here, thenasyncContext is therunning execution context again.- Returncompletion.
28 Reflection
28.1 The Reflect Object
The Reflect object:
- is%Reflect%.
- is the initial value of the
"Reflect" property of theglobal object . - is an
ordinary object . - has a[[Prototype]] internal slot whose value is
%Object.prototype% . - is not a
function object . - does not have a[[Construct]] internal method; it cannot be used as a
constructor with thenewoperator. - does not have a[[Call]] internal method; it cannot be invoked as a function.
28.1.1 Reflect.apply (target,thisArgument,argumentsList )
This function performs the following steps when called:
- If
IsCallable (target) isfalse , throw aTypeError exception. - Letargs be ?
CreateListFromArrayLike (argumentsList). - Perform
PrepareForTailCall (). - Return ?
Call (target,thisArgument,args).
28.1.2 Reflect.construct (target,argumentsList [ ,newTarget ] )
This function performs the following steps when called:
- If
IsConstructor (target) isfalse , throw aTypeError exception. - IfnewTarget is not present, setnewTarget totarget.
- Else if
IsConstructor (newTarget) isfalse , throw aTypeError exception. - Letargs be ?
CreateListFromArrayLike (argumentsList). - Return ?
Construct (target,args,newTarget).
28.1.3 Reflect.defineProperty (target,propertyKey,attributes )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Letdesc be ?
ToPropertyDescriptor (attributes). - Return ? target.[[DefineOwnProperty]](key,desc).
28.1.4 Reflect.deleteProperty (target,propertyKey )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Return ? target.[[Delete]](key).
28.1.5 Reflect.get (target,propertyKey [ ,receiver ] )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Ifreceiver is not present, then
- Setreceiver totarget.
- Return ? target.[[Get]](key,receiver).
28.1.6 Reflect.getOwnPropertyDescriptor (target,propertyKey )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Letdesc be ? target.[[GetOwnProperty]](key).
- Return
FromPropertyDescriptor (desc).
28.1.7 Reflect.getPrototypeOf (target )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Return ? target.[[GetPrototypeOf]]().
28.1.8 Reflect.has (target,propertyKey )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Return ? target.[[HasProperty]](key).
28.1.9 Reflect.isExtensible (target )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Return ? target.[[IsExtensible]]().
28.1.10 Reflect.ownKeys (target )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkeys be ? target.[[OwnPropertyKeys]]().
- Return
CreateArrayFromList (keys).
28.1.11 Reflect.preventExtensions (target )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Return ? target.[[PreventExtensions]]().
28.1.12 Reflect.set (target,propertyKey,V [ ,receiver ] )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Letkey be ?
ToPropertyKey (propertyKey). - Ifreceiver is not present, then
- Setreceiver totarget.
- Return ? target.[[Set]](key,V,receiver).
28.1.13 Reflect.setPrototypeOf (target,proto )
This function performs the following steps when called:
- Iftarget
is not an Object , throw aTypeError exception. - Ifproto
is not an Object andproto is notnull , throw aTypeError exception. - Return ? target.[[SetPrototypeOf]](proto).
28.1.14 Reflect [ @@toStringTag ]
The initial value of the
This property has the attributes {[[Writable]]:
28.2 Proxy Objects
28.2.1 The Proxy Constructor
The Proxy
- is%Proxy%.
- is the initial value of the
"Proxy" property of theglobal object . - creates and initializes a new Proxy object when called as a
constructor . - is not intended to be called as a function and will throw an exception when called in that manner.
28.2.1.1 Proxy (target,handler )
This function performs the following steps when called:
- If NewTarget is
undefined , throw aTypeError exception. - Return ?
ProxyCreate (target,handler).
28.2.2 Properties of the Proxy Constructor
The Proxy
- has a[[Prototype]] internal slot whose value is
%Function.prototype% . - does not have a
"prototype" property because Proxy objects do not have a[[Prototype]] internal slot that requires initialization. - has the following properties:
28.2.2.1 Proxy.revocable (target,handler )
This function creates a revocable Proxy object.
It performs the following steps when called:
- Letproxy be ?
ProxyCreate (target,handler). - LetrevokerClosure be a new
Abstract Closure with no parameters that captures nothing and performs the following steps when called:- LetF be the
active function object . - Letp beF.[[RevocableProxy]].
- Ifp is
null , returnundefined . - SetF.[[RevocableProxy]] to
null . Assert :p is aProxy exotic object .- Setp.[[ProxyTarget]] to
null . - Setp.[[ProxyHandler]] to
null . - Return
undefined .
- LetF be the
- Letrevoker be
CreateBuiltinFunction (revokerClosure, 0,"" , «[[RevocableProxy]] »). - Setrevoker.[[RevocableProxy]] toproxy.
- Letresult be
OrdinaryObjectCreate (%Object.prototype% ). - Perform !
CreateDataPropertyOrThrow (result,"proxy" ,proxy). - Perform !
CreateDataPropertyOrThrow (result,"revoke" ,revoker). - Returnresult.
28.3 Module Namespace Objects
A Module Namespace Object is a
In addition to the properties specified in
28.3.1 @@toStringTag
The initial value of the
This property has the attributes {[[Writable]]:
29 Memory Model
The memory consistency model, ormemory model, specifies the possible orderings of
The memory model is defined as relational constraints on events introduced by
This section provides an axiomatic model on events introduced by the
29.1 Memory Model Fundamentals
Shared memory accesses (reads and writes) are divided into two groups, atomic accesses and data accesses, defined below. Atomic accesses are sequentially consistent, i.e., there is a strict total ordering of events agreed upon by all
No orderings weaker than sequentially consistent and stronger than unordered, such as release-acquire, are supported.
AShared Data Block event is either aReadSharedMemory,WriteSharedMemory, orReadModifyWriteSharedMemory
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the | |
| [[NoTear]] | a Boolean | Whether this event is allowed to read from multiple write events with equal range as this event. |
| [[Block]] | a | The block the event operates on. |
| [[ByteIndex]] | a non-negative | The byte address of the read in[[Block]]. |
| [[ElementSize]] | a non-negative | The size of the read. |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | The weakest ordering guaranteed by the | |
| [[NoTear]] | a Boolean | Whether this event is allowed to be read from multiple read events with equal range as this event. |
| [[Block]] | a | The block the event operates on. |
| [[ByteIndex]] | a non-negative | The byte address of the write in[[Block]]. |
| [[ElementSize]] | a non-negative | The size of the write. |
| [[Payload]] | a | The |
| Field Name | Value | Meaning |
|---|---|---|
| [[Order]] | Read-modify-write events are always sequentially consistent. | |
| [[NoTear]] | Read-modify-write events cannot tear. | |
| [[Block]] | a | The block the event operates on. |
| [[ByteIndex]] | a non-negative | The byte address of the read-modify-write in[[Block]]. |
| [[ElementSize]] | a non-negative | The size of the read-modify-write. |
| [[Payload]] | a | The |
| [[ModifyOp]] | a | An abstract closure that returns a modified |
These events are introduced by
Some operations may also introduceSynchronize events. ASynchronize event has no fields, and exists purely to directly constrain the permitted orderings of other events.
In addition to
Let the range of a ReadSharedMemory, WriteSharedMemory, or ReadModifyWriteSharedMemory event be the Set of contiguous
Examples ofpostMessage in a browser), starting and stopping
Events are ordered within
29.2 Agent Events Records
AnAgent Events Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[AgentSignifier]] | an | The |
| [[EventList]] | a | Events are appended to the list during evaluation. |
| [[AgentSynchronizesWith]] | a |
29.3 Chosen Value Records
AChosen Value Record is a
| Field Name | Value | Meaning |
|---|---|---|
| [[Event]] | a | The |
| [[ChosenValue]] | a | The bytes that were nondeterministically chosen during evaluation. |
29.4 Candidate Executions
Acandidate execution of the evaluation of an
| Field Name | Value | Meaning |
|---|---|---|
| [[EventsRecords]] | a | Maps an |
| [[ChosenValues]] | a | Maps |
| [[AgentOrder]] | an | Defined below. |
| [[ReadsBytesFrom]] | a | Defined below. |
| [[ReadsFrom]] | a | Defined below. |
| [[HostSynchronizesWith]] | a | Defined below. |
| [[SynchronizesWith]] | a | Defined below. |
| [[HappensBefore]] | a | Defined below. |
Anempty candidate execution is a candidate execution
29.5 Abstract Operations for the Memory Model
29.5.1 EventSet (execution )
The abstract operation EventSet takes argumentexecution (a
- Letevents be an empty Set.
- For each
Agent Events Record aer ofexecution.[[EventsRecords]], do- For each eventE ofaer.[[EventList]], do
- AddE toevents.
- For each eventE ofaer.[[EventList]], do
- Returnevents.
29.5.2 SharedDataBlockEventSet (execution )
The abstract operation SharedDataBlockEventSet takes argumentexecution (a
- Letevents be an empty Set.
- For each eventE of
EventSet (execution), do- IfE is a
ReadSharedMemory ,WriteSharedMemory , orReadModifyWriteSharedMemory event, addE toevents.
- IfE is a
- Returnevents.
29.5.3 HostEventSet (execution )
The abstract operation HostEventSet takes argumentexecution (a
- Letevents be an empty Set.
- For each eventE of
EventSet (execution), do- IfE is not in
SharedDataBlockEventSet (execution), addE toevents.
- IfE is not in
- Returnevents.
29.5.4 ComposeWriteEventBytes (execution,byteIndex,Ws )
The abstract operation ComposeWriteEventBytes takes argumentsexecution (a
- LetbyteLocation bebyteIndex.
- LetbytesRead be a new empty
List . - For each elementW ofWs, do
Assert :W hasbyteLocation in its range.- LetpayloadIndex bebyteLocation -W.[[ByteIndex]].
- IfW is a
WriteSharedMemory event, then- Letbyte beW.[[Payload]][payloadIndex].
- Else,
Assert :W is aReadModifyWriteSharedMemory event.- Letbytes be
ValueOfReadEvent (execution,W). - LetbytesModified beW.[[ModifyOp]](bytes,W.[[Payload]]).
- Letbyte bebytesModified[payloadIndex].
- Appendbyte tobytesRead.
- SetbyteLocation tobyteLocation + 1.
- ReturnbytesRead.
The read-modify-write modification[[ModifyOp]] is given by the function properties on the Atomics object that introduce
This abstract operation composes a
29.5.5 ValueOfReadEvent (execution,R )
The abstract operation ValueOfReadEvent takes argumentsexecution (a
- LetWs beexecution.[[ReadsBytesFrom]](R).
Assert :Ws is aList ofWriteSharedMemory orReadModifyWriteSharedMemory events with length equal toR.[[ElementSize]].- Return
ComposeWriteEventBytes (execution,R.[[ByteIndex]],Ws).
29.6 Relations of Candidate Executions
29.6.1 agent-order
For a
- For each pair (E,D) in
EventSet (execution),execution.[[AgentOrder]] contains (E,D) if there is someAgent Events Record aer inexecution.[[EventsRecords]] such thatE andD are inaer.[[EventList]] andE is beforeD inList order ofaer.[[EventList]].
Each
29.6.2 reads-bytes-from
For a
For each
ReadSharedMemory orReadModifyWriteSharedMemory eventR inSharedDataBlockEventSet (execution),execution.[[ReadsBytesFrom]](R) is aList of lengthR.[[ElementSize]] whose elements areWriteSharedMemory orReadModifyWriteSharedMemory eventsWs such that all of the following are true.- Each eventW with indexi inWs hasR.[[ByteIndex]] +i in its range.
- R is not inWs.
29.6.3 reads-from
For a
- For each pair (R,W) in
SharedDataBlockEventSet (execution),execution.[[ReadsFrom]] contains (R,W) ifexecution.[[ReadsBytesFrom]](R) containsW.
29.6.4 host-synchronizes-with
For a
- Ifexecution.[[HostSynchronizesWith]] contains (E,D),E andD are in
HostEventSet (execution). - There is no cycle in the union ofexecution.[[HostSynchronizesWith]] andexecution.[[AgentOrder]].
For two
The host-synchronizes-with relation allows thepostMessage between HTML workers.
29.6.5 synchronizes-with
For a
- For each pair (R,W) inexecution.[[ReadsFrom]],execution.[[SynchronizesWith]] contains (W,R) ifR.[[Order]] is
seq-cst ,W.[[Order]] isseq-cst , andR andW have equal ranges. - For each elementeventsRecord ofexecution.[[EventsRecords]], the following is true.
- For each pair (S,Sw) ineventsRecord.[[AgentSynchronizesWith]],execution.[[SynchronizesWith]] contains (S,Sw).
- For each pair (E,D) inexecution.[[HostSynchronizesWith]],execution.[[SynchronizesWith]] contains (E,D).
Owing to convention, write events synchronizes-with read events, instead of read events synchronizes-with write events.
Not all
For
29.6.6 happens-before
For a
- For each pair (E,D) inexecution.[[AgentOrder]],execution.[[HappensBefore]] contains (E,D).
- For each pair (E,D) inexecution.[[SynchronizesWith]],execution.[[HappensBefore]] contains (E,D).
- For each pair (E,D) in
SharedDataBlockEventSet (execution),execution.[[HappensBefore]] contains (E,D) ifE.[[Order]] isinit andE andD have overlapping ranges. - For each pair (E,D) in
EventSet (execution),execution.[[HappensBefore]] contains (E,D) if there is an eventF such that the pairs (E,F) and (F,D) are inexecution.[[HappensBefore]].
Because happens-before is a superset of
29.7 Properties of Valid Executions
29.7.1 Valid Chosen Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory eventR ofSharedDataBlockEventSet (execution), do- LetchosenValueRecord be the element ofexecution.[[ChosenValues]] whose[[Event]] field isR.
- LetchosenValue bechosenValueRecord.[[ChosenValue]].
- LetreadValue be
ValueOfReadEvent (execution,R). - LetchosenLen be the number of elements inchosenValue.
- LetreadLen be the number of elements inreadValue.
- IfchosenLen ≠readLen, then
- Return
false .
- Return
- IfchosenValue[i] ≠readValue[i] for some
integer i in theinterval from 0 (inclusive) tochosenLen (exclusive), then- Return
false .
- Return
- Return
true .
29.7.2 Coherent Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory eventR ofSharedDataBlockEventSet (execution), do- LetWs beexecution.[[ReadsBytesFrom]](R).
- LetbyteLocation beR.[[ByteIndex]].
- For each elementW ofWs, do
- Ifexecution.[[HappensBefore]] contains (R,W), then
- Return
false .
- Return
- If there exists a
WriteSharedMemory orReadModifyWriteSharedMemory eventV that hasbyteLocation in its range such that the pairs (W,V) and (V,R) are inexecution.[[HappensBefore]], then- Return
false .
- Return
- SetbyteLocation tobyteLocation + 1.
- Ifexecution.[[HappensBefore]] contains (R,W), then
- Return
true .
29.7.3 Tear Free Reads
A
- For each
ReadSharedMemory orReadModifyWriteSharedMemory eventR ofSharedDataBlockEventSet (execution), do- IfR.[[NoTear]] is
true , thenAssert : The remainder of dividingR.[[ByteIndex]] byR.[[ElementSize]] is 0.- For each eventW such thatexecution.[[ReadsFrom]] contains (R,W) andW.[[NoTear]] is
true , do- IfR andW have equal ranges and there exists an eventV such thatV andW have equal ranges,V.[[NoTear]] is
true ,W is notV, andexecution.[[ReadsFrom]] contains (R,V), then- Return
false .
- Return
- IfR andW have equal ranges and there exists an eventV such thatV andW have equal ranges,V.[[NoTear]] is
- IfR.[[NoTear]] is
- Return
true .
An event's[[NoTear]] field is
Intuitively, this requirement says when a memory range is accessed in an aligned fashion via an
29.7.4 Sequentially Consistent Atomics
For a
- For each pair (E,D) inexecution.[[HappensBefore]], (E,D) is in memory-order.
For each pair (R,W) inexecution.[[ReadsFrom]], there is no
WriteSharedMemory orReadModifyWriteSharedMemory eventV inSharedDataBlockEventSet (execution) such thatV.[[Order]] isseq-cst , the pairs (W,V) and (V,R) are in memory-order, and any of the following conditions are true.- execution.[[SynchronizesWith]] contains the pair (W,R), andV andR have equal ranges.
- The pairs (W,R) and (V,R) are inexecution.[[HappensBefore]],W.[[Order]] is
seq-cst , andW andV have equal ranges. - The pairs (W,R) and (W,V) are inexecution.[[HappensBefore]],R.[[Order]] is
seq-cst , andV andR have equal ranges.
Note 1 This clause additionally constrains
seq-cst events on equal ranges.For each
WriteSharedMemory orReadModifyWriteSharedMemory eventW inSharedDataBlockEventSet (execution), ifW.[[Order]] isseq-cst , then it is not the case that there is an infinite number ofReadSharedMemory orReadModifyWriteSharedMemory events inSharedDataBlockEventSet (execution) with equal range that is memory-order beforeW.Note 2
A
While memory-order includes all events in
29.7.5 Valid Executions
A
- The
host provides ahost-synchronizes-with Relation forexecution.[[HostSynchronizesWith]]. - execution.[[HappensBefore]] is a
strict partial order . - execution has valid chosen reads.
- execution has coherent reads.
- execution has tear free reads.
- execution has sequentially consistent atomics.
All programs have at least one valid execution.
29.8 Races
For an executionexecution, two eventsE andD in
- IfE is notD, then
- If the pairs (E,D) and (D,E) are not inexecution.[[HappensBefore]], then
- IfE andD are both
WriteSharedMemory orReadModifyWriteSharedMemory events andE andD do not have disjoint ranges, then- Return
true .
- Return
- Ifexecution.[[ReadsFrom]] contains either (E,D) or (D,E), then
- Return
true .
- Return
- IfE andD are both
- If the pairs (E,D) and (D,E) are not inexecution.[[HappensBefore]], then
- Return
false .
29.9 Data Races
For an executionexecution, two eventsE andD in
- IfE andD are in a race inexecution, then
- IfE.[[Order]] is not
seq-cst orD.[[Order]] is notseq-cst , then- Return
true .
- Return
- IfE andD have overlapping ranges, then
- Return
true .
- Return
- IfE.[[Order]] is not
- Return
false .
29.10 Data Race Freedom
An executionexecution is data race free if there are no two events in
A program is data race free if all its executions are data race free.
The
29.11 Shared Memory Guidelines
The following are guidelines for ECMAScript programmers working with shared memory.
We recommend programs be kept data race free, i.e., make it so that it is impossible for there to be concurrent non-atomic operations on the same memory location. Data race free programs have interleaving semantics where each step in the evaluation semantics of each
More generally, even if a program is not data race free it may have predictable behaviour, so long as atomic operations are not involved in any data races and the operations that race all have the same access size. The simplest way to arrange for atomics not to be involved in races is to ensure that different memory cells are used by atomic and non-atomic operations and that atomic accesses of different sizes are not used to access the same cells at the same time. Effectively, the program should treat shared memory as strongly typed as much as possible. One still cannot depend on the ordering and timing of non-atomic accesses that race, but if memory is treated as strongly typed the racing accesses will not "tear" (bits of their values will not be mixed).
The following are guidelines for ECMAScript implementers writing compiler transformations for programs using shared memory.
It is desirable to allow most program transformations that are valid in a single-
Let anagent-order slice be the subset of the
Letpossible read values of a read event be the set of all values of
Any transformation of an agent-order slice that is valid in the absence of shared memory is valid in the presence of shared memory, with the following exceptions.
Atomics are carved in stone: Program transformations must not cause the
seq-cst events in an agent-order slice to be reordered with itsunordered operations, nor itsseq-cst operations to be reordered with each other, nor may a program transformation remove aseq-cst operation from theagent-order .(In practice, the prohibition on reorderings forces a compiler to assume that every
seq-cst operation is a synchronization and included in the finalmemory-order , which it would usually have to assume anyway in the absence of inter-agent program analysis. It also forces the compiler to assume that every call where the callee's effects on thememory-order are unknown may containseq-cst operations.)Reads must be stable: Any given shared memory read must only observe a single value in an execution.
(For example, if what is semantically a single read in the program is executed multiple times then the program is subsequently allowed to observe only one of the values read. A transformation known as rematerialization can violate this rule.)
Writes must be stable: All observable writes to shared memory must follow from program semantics in an execution.
(For example, a transformation may not introduce certain observable writes, such as by using read-modify-write operations on a larger location to write a smaller datum, writing a value to memory that the program could not have written, or writing a just-read value back to the location it was read from, if that location could have been overwritten by another
agent after the read.)Possible read values must be non-empty: Program transformations cannot cause the possible read values of a shared memory read to become empty.
(Counterintuitively, this rule in effect restricts transformations on writes, because writes have force in
memory model insofar as to be read by read events. For example, writes may be moved and coalesced and sometimes reordered between twoseq-cst operations, but the transformation may not remove every write that updates a location; some write must be preserved.)
Examples of transformations that remain valid are: merging multiple non-atomic reads from the same location, reordering non-atomic reads, introducing speculative non-atomic reads, merging multiple non-atomic writes to the same location, reordering non-atomic writes to different locations, and hoisting non-atomic reads out of loops even if that affects termination. Note in general that aliased
The following are guidelines for ECMAScript implementers generating machine code for shared memory accesses.
For architectures with memory models no weaker than those of ARM or Power, non-atomic stores and loads may be compiled to bare stores and loads on the target architecture. Atomic stores and loads may be compiled down to instructions that guarantee sequential consistency. If no such instructions exist, memory barriers are to be employed, such as placing barriers on both sides of a bare store or load. Read-modify-write operations may be compiled to read-modify-write instructions on the target architecture, such asLOCK-prefixed instructions on x86, load-exclusive/store-exclusive instructions on ARM, and load-link/store-conditional instructions on Power.
Specifically, the
- Every atomic operation in the program is assumed to be necessary.
- Atomic operations are never rearranged with each other or with non-atomic operations.
- Functions are always assumed to perform atomic operations.
- Atomic operations are never implemented as read-modify-write operations on larger data, but as non-lock-free atomics if the platform does not have atomic operations of the appropriate size. (We already assume that every platform has normal memory access operations of every interesting size.)
Naive code generation uses these patterns:
- Regular loads and stores compile to single load and store instructions.
- Lock-free atomic loads and stores compile to a full (sequentially consistent) fence, a regular load or store, and a full fence.
- Lock-free atomic read-modify-write accesses compile to a full fence, an atomic read-modify-write instruction sequence, and a full fence.
- Non-lock-free atomics compile to a spinlock acquire, a full fence, a series of non-atomic load and store instructions, a full fence, and a spinlock release.
That mapping is correct so long as an atomic operation on an address range does not race with a non-atomic write or with an atomic operation of different size. However, that is all we need: the
Local improvements to those basic patterns are also allowed, subject to the constraints of the
- There are obvious platform-dependent improvements that remove redundant fences. For example, on x86 the fences around lock-free atomic loads and stores can always be omitted except for the fence following a store, and no fence is needed for lock-free read-modify-write instructions, as these all use
LOCK-prefixed instructions. On many platforms there are fences of several strengths, and weaker fences can be used in certain contexts without destroying sequential consistency. - Most modern platforms support lock-free atomics for all the data sizes required by ECMAScript atomics. Should non-lock-free atomics be needed, the fences surrounding the body of the atomic operation can usually be folded into the lock and unlock steps. The simplest solution for non-lock-free atomics is to have a single lock word per SharedArrayBuffer.
- There are also more complicated platform-dependent local improvements, requiring some code analysis. For example, two back-to-back fences often have the same effect as a single fence, so if code is generated for two atomic operations in sequence, only a single fence need separate them. On x86, even a single fence separating atomic stores can be omitted, as the fence following a store is only needed to separate the store from a subsequent load.
A Grammar Summary
A.1 Lexical Grammar
A.2 Expressions
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
In certain circumstances when processing an instance of the production
the interpretation of
A.3 Statements
A.4 Functions and Classes
When processing an instance of the production
the interpretation of
When processing an instance of the production
the interpretation of
A.5 Scripts and Modules
A.6 Number Conversions
All grammar symbols not explicitly defined by the
A.7 Time Zone Offset String Format
A.8 Regular Expressions
Each\uuu\u
B Additional ECMAScript Features for Web Browsers
The ECMAScript language syntax and semantics defined in this annex are required when the ECMAScript
This annex describes various legacy features and other characteristics of web browser ECMAScript
These features are not considered part of the core ECMAScript language. Programmers should not use or assume the existence of these features and behaviours when writing new ECMAScript code. ECMAScript implementations are discouraged from implementing these features unless the implementation is part of a web browser or is required to run the same legacy ECMAScript code that web browsers encounter.
B.1 Additional Syntax
B.1.1 HTML-like Comments
The syntax and semantics of
Syntax
Similar to a
B.1.2 Regular Expressions Patterns
The syntax of
This alternative pattern grammar and semantics only changes the syntax and semantics of BMP patterns. The following grammar extensions include productions parameterized with the [UnicodeMode] parameter. However, none of these extensions change the syntax of Unicode patterns recognized when parsing with the [UnicodeMode] parameter present on the
Syntax
When the same left-hand sides occurs with both [+UnicodeMode] and [~UnicodeMode] guards it is to control the disambiguation priority.
B.1.2.1 Static Semantics: Early Errors
The semantics of
- It is a Syntax Error if any source text is matched by this production.
Additionally, the rules for the following productions are modified with the addition of thehighlighted text:
- It is a Syntax Error if
IsCharacterClass of the firstClassAtom istrue orIsCharacterClass of the secondClassAtom istrue and this production has a[UnicodeMode] parameter. - It is a Syntax Error if
IsCharacterClass of the firstClassAtom isfalse ,IsCharacterClass of the secondClassAtom isfalse , and theCharacterValue of the firstClassAtom is strictly greater than theCharacterValue of the secondClassAtom .
- It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash istrue orIsCharacterClass ofClassAtom istrue and this production has a[UnicodeMode] parameter. - It is a Syntax Error if
IsCharacterClass ofClassAtomNoDash isfalse ,IsCharacterClass ofClassAtom isfalse , and theCharacterValue ofClassAtomNoDash is strictly greater than theCharacterValue ofClassAtom .
B.1.2.2 Static Semantics: CountLeftCapturingParensWithin and CountLeftCapturingParensBefore
In the definitions of
B.1.2.3 Static Semantics: IsCharacterClass
The semantics of
- Return
false .
B.1.2.4 Static Semantics: CharacterValue
The semantics of
- Return the numeric value of U+005C (REVERSE SOLIDUS).
- Letch be the code point matched by
ClassControlLetter . - Leti be the numeric value ofch.
- Return the remainder of dividingi by 32.
- Return the MV of
LegacyOctalEscapeSequence (see12.9.4.3 ).
B.1.2.5 Runtime Semantics: CompileSubpattern
The semantics of
The rule for
The rule for
The rule for
B.1.2.6 Runtime Semantics: CompileAssertion
B.1.2.7 Runtime Semantics: CompileAtom
- LetA be the
CharSet containing the single character\U+005C (REVERSE SOLIDUS). - Return
CharacterSetMatcher (rer,A,false ,direction).
- Letch be the character represented by
ExtendedPatternCharacter . - LetA be a one-element
CharSet containing the characterch. - Return
CharacterSetMatcher (rer,A,false ,direction).
B.1.2.8 Runtime Semantics: CompileToCharSet
The semantics of
The following two rules replace the corresponding rules of
- LetA be
CompileToCharSet of the firstClassAtom with argumentrer. - LetB be
CompileToCharSet of the secondClassAtom with argumentrer. - LetC be
CompileToCharSet ofClassContents with argumentrer. - LetD be
CharacterRangeOrUnion (rer,A,B). - Return the union ofD andC.
- LetA be
CompileToCharSet ofClassAtomNoDash with argumentrer. - LetB be
CompileToCharSet ofClassAtom with argumentrer. - LetC be
CompileToCharSet ofClassContents with argumentrer. - LetD be
CharacterRangeOrUnion (rer,A,B). - Return the union ofD andC.
In addition, the following rules are added to
- Letcv be the
CharacterValue of thisClassEscape . - Letc be the character whose character value iscv.
- Return the
CharSet containing the single characterc.
- Return the
CharSet containing the single character\U+005C (REVERSE SOLIDUS).
\c within a character class where it is not followed by an acceptable control character.B.1.2.8.1 CharacterRangeOrUnion (rer,A,B )
The abstract operation CharacterRangeOrUnion takes argumentsrer (a
- If
HasEitherUnicodeFlag (rer) isfalse , then - Return
CharacterRange (A,B).
B.1.2.9 Static Semantics: ParsePattern (patternText,u,v )
The semantics of
The abstract operation
- Ifv is
true andu istrue , then- LetparseResult be a
List containing one or moreSyntaxError objects.
- LetparseResult be a
- Else ifv is
true , then - Else ifu is
true , then - Else,
- ReturnparseResult.
B.2 Additional Built-in Properties
When the ECMAScript
B.2.1 Additional Properties of the Global Object
The entries in
| Intrinsic Name | Global Name | ECMAScript Language Association |
|---|---|---|
escape | Theescape function ( | |
unescape | Theunescape function ( |
B.2.1.1 escape (string )
This function is a property of the
When replacing a code unit of numeric value less than or equal to 0x00FF, a two-digit escape sequence of the form%xx is used. When replacing a code unit of numeric value strictly greater than 0x00FF, a four-digit escape sequence of the form%uxxxx is used.
It is the%escape% intrinsic object.
It performs the following steps when called:
- Setstring to ?
ToString (string). - Letlen be the length ofstring.
- LetR be the empty String.
- LetunescapedSet be the
string-concatenation ofthe ASCII word characters and"@*+-./" . - Letk be 0.
- Repeat, whilek <len,
- LetC be the code unit at indexk withinstring.
- IfunescapedSet containsC, then
- LetS beC.
- Else,
- Letn be the numeric value ofC.
- Ifn < 256, then
- Lethex be the String representation ofn, formatted as an uppercase hexadecimal number.
- LetS be the
string-concatenation of"%" andStringPad (hex, 2,"0" ,start ).
- Else,
- Lethex be the String representation ofn, formatted as an uppercase hexadecimal number.
- LetS be the
string-concatenation of"%u" andStringPad (hex, 4,"0" ,start ).
- SetR to the
string-concatenation ofR andS. - Setk tok + 1.
- ReturnR.
The encoding is partly based on the encoding described in RFC 1738, but the entire encoding specified in this standard is described above without regard to the contents of RFC 1738. This encoding does not reflect changes to RFC 1738 made by RFC 3986.
B.2.1.2 unescape (string )
This function is a property of theescape function is replaced with the code unit that it represents.
It is the%unescape% intrinsic object.
It performs the following steps when called:
- Setstring to ?
ToString (string). - Letlen be the length ofstring.
- LetR be the empty String.
- Letk be 0.
- Repeat, whilek <len,
- LetC be the code unit at indexk withinstring.
- IfC is the code unit 0x0025 (PERCENT SIGN), then
- LethexDigits be the empty String.
- LetoptionalAdvance be 0.
- Ifk + 5 <len and the code unit at indexk + 1 withinstring is the code unit 0x0075 (LATIN SMALL LETTER U), then
- SethexDigits to the
substring ofstring fromk + 2 tok + 6. - SetoptionalAdvance to 5.
- SethexDigits to the
- Else ifk + 3 ≤len, then
- SethexDigits to the
substring ofstring fromk + 1 tok + 3. - SetoptionalAdvance to 2.
- SethexDigits to the
- LetparseResult be
ParseText (StringToCodePoints (hexDigits),HexDigits ).[~Sep] - IfparseResult is a
Parse Node , then- Letn be the MV ofparseResult.
- SetC to the code unit whose numeric value isn.
- Setk tok +optionalAdvance.
- SetR to the
string-concatenation ofR andC. - Setk tok + 1.
- ReturnR.
B.2.2 Additional Properties of the String.prototype Object
B.2.2.1 String.prototype.substr (start,length )
This method returns a
It performs the following steps when called:
- LetO be ?
RequireObjectCoercible (this value). - LetS be ?
ToString (O). - Letsize be the length ofS.
- LetintStart be ?
ToIntegerOrInfinity (start). - IfintStart = -∞, setintStart to 0.
- Else ifintStart < 0, setintStart to
max (size +intStart, 0). - Else, setintStart to
min (intStart,size). - Iflength is
undefined , letintLength besize; otherwise letintLength be ?ToIntegerOrInfinity (length). - SetintLength to the result of
clamping intLength between 0 andsize. - LetintEnd be
min (intStart +intLength,size). - Return the
substring ofS fromintStart tointEnd.
This method is intentionally generic; it does not require that its
B.2.2.2 String.prototype.anchor (name )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"a" ,"name" ,name).
B.2.2.2.1 CreateHTML (string,tag,attribute,value )
The abstract operation CreateHTML takes argumentsstring (an
- Letstr be ?
RequireObjectCoercible (string). - LetS be ?
ToString (str). - Letp1 be the
string-concatenation of"<" andtag. - Ifattribute is not the empty String, then
- LetV be ?
ToString (value). - LetescapedV be the String value that is the same asV except that each occurrence of the code unit 0x0022 (QUOTATION MARK) inV has been replaced with the six code unit sequence
""" . - Setp1 to the
string-concatenation of:- p1
- the code unit 0x0020 (SPACE)
- attribute
- the code unit 0x003D (EQUALS SIGN)
- the code unit 0x0022 (QUOTATION MARK)
- escapedV
- the code unit 0x0022 (QUOTATION MARK)
- LetV be ?
- Letp2 be the
string-concatenation ofp1 and">" . - Letp3 be the
string-concatenation ofp2 andS. - Letp4 be the
string-concatenation ofp3,"</" ,tag, and">" . - Returnp4.
B.2.2.3 String.prototype.big ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"big" ,"" ,"" ).
B.2.2.4 String.prototype.blink ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"blink" ,"" ,"" ).
B.2.2.5 String.prototype.bold ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"b" ,"" ,"" ).
B.2.2.6 String.prototype.fixed ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"tt" ,"" ,"" ).
B.2.2.7 String.prototype.fontcolor (color )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"font" ,"color" ,color).
B.2.2.8 String.prototype.fontsize (size )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"font" ,"size" ,size).
B.2.2.9 String.prototype.italics ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"i" ,"" ,"" ).
B.2.2.10 String.prototype.link (url )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"a" ,"href" ,url).
B.2.2.11 String.prototype.small ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"small" ,"" ,"" ).
B.2.2.12 String.prototype.strike ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"strike" ,"" ,"" ).
B.2.2.13 String.prototype.sub ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"sub" ,"" ,"" ).
B.2.2.14 String.prototype.sup ( )
This method performs the following steps when called:
- LetS be the
this value. - Return ?
CreateHTML (S,"sup" ,"" ,"" ).
B.2.2.15 String.prototype.trimLeft ( )
The property
The initial value of the
B.2.2.16 String.prototype.trimRight ( )
The property
The initial value of the
B.2.3 Additional Properties of the Date.prototype Object
B.2.3.1 Date.prototype.getYear ( )
ThegetFullYear method is preferred for nearly all purposes, because it avoids the “year 2000 problem.”
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Ift is
NaN , returnNaN . - Return
YearFromTime (LocalTime (t)) -1900 𝔽.
B.2.3.2 Date.prototype.setYear (year )
ThesetFullYear method is preferred for nearly all purposes, because it avoids the “year 2000 problem.”
This method performs the following steps when called:
- LetdateObject be the
this value. - Perform ?
RequireInternalSlot (dateObject,[[DateValue]]). - Lett bedateObject.[[DateValue]].
- Lety be ?
ToNumber (year). - Ift is
NaN , sett to+0 𝔽; otherwise, sett toLocalTime (t). - Letyyyy be
MakeFullYear (y). - Letd be
MakeDay (yyyy,MonthFromTime (t),DateFromTime (t)). - Letdate be
MakeDate (d,TimeWithinDay (t)). - Letu be
TimeClip (UTC (date)). - SetdateObject.[[DateValue]] tou.
- Returnu.
B.2.3.3 Date.prototype.toGMTString ( )
ThetoUTCString method is preferred. This method is provided principally for compatibility with old code.
The initial value of the
B.2.4 Additional Properties of the RegExp.prototype Object
B.2.4.1 RegExp.prototype.compile (pattern,flags )
This method performs the following steps when called:
- LetO be the
this value. - Perform ?
RequireInternalSlot (O,[[RegExpMatcher]]). - Ifpattern
is an Object andpattern has a[[RegExpMatcher]] internal slot, then- Ifflags is not
undefined , throw aTypeError exception. - LetP bepattern.[[OriginalSource]].
- LetF bepattern.[[OriginalFlags]].
- Ifflags is not
- Else,
- LetP bepattern.
- LetF beflags.
- Return ?
RegExpInitialize (O,P,F).
This method completely reinitializes the
B.3 Other Additional Features
B.3.1 Labelled Function Declarations
Prior to ECMAScript 2015, the specification of
- It is a Syntax Error if any source textthat is
strict mode code is matched by this production.
The
B.3.2 Block-Level Function Declarations Web Legacy Compatibility Semantics
Prior to ECMAScript 2015, the ECMAScript specification did not define the occurrence of a
A function is declared and only referenced within a single block.
- One or more
FunctionDeclaration s whoseBindingIdentifier is the namef occur within the function code of an enclosing functiong and that declaration is nested within aBlock . - No other declaration off that is not a
vardeclaration occurs within the function code ofg. - All occurrences off as an
IdentifierReference are within theStatementList of theBlock containing the declaration off.
- One or more
A function is declared and possibly used within a single
Block but also referenced by an inner function definition that is not contained within that sameBlock .- One or more
FunctionDeclaration s whoseBindingIdentifier is the namef occur within the function code of an enclosing functiong and that declaration is nested within aBlock . - No other declaration off that is not a
vardeclaration occurs within the function code ofg. - There may be occurrences off as an
IdentifierReference within theStatementList of theBlock containing the declaration off. - There is at least one occurrence off as an
IdentifierReference within another functionh that is nested withing and no other declaration off shadows the references tof from withinh. - All invocations ofh occur after the declaration off has been evaluated.
- One or more
A function is declared and possibly used within a single block but also referenced within subsequent blocks.
- One or more
FunctionDeclaration whoseBindingIdentifier is the namef occur within the function code of an enclosing functiong and that declaration is nested within aBlock . - No other declaration off that is not a
vardeclaration occurs within the function code ofg. - There may be occurrences off as an
IdentifierReference within theStatementList of theBlock containing the declaration off. - There is at least one occurrence off as an
IdentifierReference within the function code ofg that lexically follows theBlock containing the declaration off.
- One or more
The first use case is interoperable with the semantics of
ECMAScript 2015 interoperability for the second and third use cases requires the following extensions to the clause
If an ECMAScript implementation has a mechanism for reporting diagnostic warning messages, a warning should be produced when code contains a
B.3.2.1 Changes to FunctionDeclarationInstantiation
During
- Ifstrict is
false , then- For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause , do- LetF be
StringValue of theBindingIdentifier off. - If replacing the
FunctionDeclaration f with aVariableStatement that hasF as aBindingIdentifier would not produce any Early Errors forfunc andparameterNames does not containF, then- NOTE: A var binding forF is only instantiated here if it is neither a VarDeclaredName, the name of a formal parameter, or another
FunctionDeclaration . - IfinstantiatedVarNames does not containF andF is not
"arguments" , then- Perform ! varEnv.CreateMutableBinding(F,
false ). - Perform ! varEnv.InitializeBinding(F,
undefined ). - AppendF toinstantiatedVarNames.
- Perform ! varEnv.CreateMutableBinding(F,
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Letfenv be the
running execution context 's VariableEnvironment. - Letbenv be the
running execution context 's LexicalEnvironment. - Letfobj be ! benv.GetBindingValue(F,
false ). - Perform ! fenv.SetMutableBinding(F,fobj,
false ). - Return
unused .
- Letfenv be the
- NOTE: A var binding forF is only instantiated here if it is neither a VarDeclaredName, the name of a formal parameter, or another
- LetF be
- For each
B.3.2.2 Changes to GlobalDeclarationInstantiation
During
- Perform the following steps:
- Letstrict be
IsStrict ofscript. - Ifstrict is
false , then- LetdeclaredFunctionOrVarNames be the
list-concatenation ofdeclaredFunctionNames anddeclaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause Contained withinscript, do- LetF be
StringValue of theBindingIdentifier off. - If replacing the
FunctionDeclaration f with aVariableStatement that hasF as aBindingIdentifier would not produce any Early Errors forscript, then- Ifenv.HasLexicalDeclaration(F) is
false , then- LetfnDefinable be ? env.CanDeclareGlobalVar(F).
- IffnDefinable is
true , then- NOTE: A var binding forF is only instantiated here if it is neither a VarDeclaredName nor the name of another
FunctionDeclaration . - IfdeclaredFunctionOrVarNames does not containF, then
- Perform ? env.CreateGlobalVarBinding(F,
false ). - AppendF todeclaredFunctionOrVarNames.
- Perform ? env.CreateGlobalVarBinding(F,
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Letgenv be the
running execution context 's VariableEnvironment. - Letbenv be the
running execution context 's LexicalEnvironment. - Letfobj be ! benv.GetBindingValue(F,
false ). - Perform ? genv.SetMutableBinding(F,fobj,
false ). - Return
unused .
- Letgenv be the
- NOTE: A var binding forF is only instantiated here if it is neither a VarDeclaredName nor the name of another
- Ifenv.HasLexicalDeclaration(F) is
- LetF be
- LetdeclaredFunctionOrVarNames be the
- Letstrict be
B.3.2.3 Changes to EvalDeclarationInstantiation
During
- Ifstrict is
false , then- LetdeclaredFunctionOrVarNames be the
list-concatenation ofdeclaredFunctionNames anddeclaredVarNames. - For each
FunctionDeclaration f that is directly contained in theStatementList of aBlock ,CaseClause , orDefaultClause Contained withinbody, do- LetF be
StringValue of theBindingIdentifier off. - If replacing the
FunctionDeclaration f with aVariableStatement that hasF as aBindingIdentifier would not produce any Early Errors forbody, then- LetbindingExists be
false . - LetthisEnv belexEnv.
Assert : The following loop will terminate.- Repeat, whilethisEnv is notvarEnv,
- IfthisEnv
is not an Object Environment Record , then- If ! thisEnv.HasBinding(F) is
true , then- LetbindingExists be
true .
- LetbindingExists be
- If ! thisEnv.HasBinding(F) is
- SetthisEnv tothisEnv.[[OuterEnv]].
- IfthisEnv
- IfbindingExists is
false andvarEnv is aGlobal Environment Record , then- IfvarEnv.HasLexicalDeclaration(F) is
false , then- LetfnDefinable be ? varEnv.CanDeclareGlobalVar(F).
- Else,
- LetfnDefinable be
false .
- LetfnDefinable be
- IfvarEnv.HasLexicalDeclaration(F) is
- Else,
- LetfnDefinable be
true .
- LetfnDefinable be
- IfbindingExists is
false andfnDefinable istrue , then- IfdeclaredFunctionOrVarNames does not containF, then
- IfvarEnv is a
Global Environment Record , then- Perform ? varEnv.CreateGlobalVarBinding(F,
true ).
- Perform ? varEnv.CreateGlobalVarBinding(F,
- Else,
- LetbindingExists be ! varEnv.HasBinding(F).
- IfbindingExists is
false , then- Perform ! varEnv.CreateMutableBinding(F,
true ). - Perform ! varEnv.InitializeBinding(F,
undefined ).
- Perform ! varEnv.CreateMutableBinding(F,
- AppendF todeclaredFunctionOrVarNames.
- IfvarEnv is a
- When the
FunctionDeclaration f is evaluated, perform the following steps in place of theFunctionDeclaration Evaluation algorithm provided in15.2.6 :- Letgenv be the
running execution context 's VariableEnvironment. - Letbenv be the
running execution context 's LexicalEnvironment. - Letfobj be ! benv.GetBindingValue(F,
false ). - Perform ? genv.SetMutableBinding(F,fobj,
false ). - Return
unused .
- Letgenv be the
- IfdeclaredFunctionOrVarNames does not containF, then
- LetbindingExists be
- LetF be
- LetdeclaredFunctionOrVarNames be the
B.3.2.4 Changes to Block Static Semantics: Early Errors
The rules for the following production in
- It is a Syntax Error if the
LexicallyDeclaredNames ofStatementList contains any duplicate entries, unless thesource text matched by this production is notstrict mode code and the duplicate entries are only bound by FunctionDeclarations. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofStatementList also occurs in theVarDeclaredNames ofStatementList .
B.3.2.5 Changes toswitch Statement Static Semantics: Early Errors
The rules for the following production in
- It is a Syntax Error if the
LexicallyDeclaredNames ofCaseBlock contains any duplicate entries, unless thesource text matched by this production is notstrict mode code and the duplicate entries are only bound by FunctionDeclarations. - It is a Syntax Error if any element of the
LexicallyDeclaredNames ofCaseBlock also occurs in theVarDeclaredNames ofCaseBlock .
B.3.2.6 Changes to BlockDeclarationInstantiation
During
- If ! env.HasBinding(dn) is
false , then- Perform ! env.CreateMutableBinding(dn,
false ).
- Perform ! env.CreateMutableBinding(dn,
During
- Perform the following steps:
- If the binding forfn inenv is an uninitialized binding, then
- Perform ! env.InitializeBinding(fn,fo).
- Else,
Assert :d is aFunctionDeclaration .- Perform ! env.SetMutableBinding(fn,fo,
false ).
- If the binding forfn inenv is an uninitialized binding, then
B.3.3 FunctionDeclarations in IfStatement Statement Clauses
The following augments the
This production only applies when parsing
B.3.4 VariableStatements in Catch Blocks
The content of subclause
- It is a Syntax Error if
BoundNames ofCatchParameter contains any duplicate elements. - It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theLexicallyDeclaredNames ofBlock . - It is a Syntax Error if any element of the
BoundNames ofCatchParameter also occurs in theVarDeclaredNames ofBlock unlessCatchParameter isCatchParameter : BindingIdentifier
Thevar declarations that bind a name that is also bound by thevar declarations will assign to the corresponding catch parameter rather than thevar binding.
This modified behaviour also applies tovar andfunction declarations introduced by
Step
- IfthisEnv is not the
Environment Record for aCatch clause, throw aSyntaxError exception.
Step
- IfthisEnv is not the
Environment Record for aCatch clause, letbindingExists betrue .
B.3.5 Initializers in ForIn Statement Heads
The following augments the
This production only applies when parsing
The
- Return
ContainsDuplicateLabels ofStatement with argumentlabelSet.
The
- Return
ContainsUndefinedBreakTarget ofStatement with argumentlabelSet.
The
- Return
ContainsUndefinedContinueTarget ofStatement with argumentsiterationSet and « ».
The
- Return
false .
The
- Letnames1 be the
BoundNames ofBindingIdentifier . - Letnames2 be the
VarDeclaredNames ofStatement . - Return the
list-concatenation ofnames1 andnames2.
The
- Letdeclarations1 be «
BindingIdentifier ». - Letdeclarations2 be the
VarScopedDeclarations ofStatement . - Return the
list-concatenation ofdeclarations1 anddeclarations2.
The
- LetbindingId be
StringValue ofBindingIdentifier . - Letlhs be ?
ResolveBinding (bindingId). - If
IsAnonymousFunctionDefinition (Initializer ) istrue , then- Letvalue be ?
NamedEvaluation ofInitializer with argumentbindingId.
- Letvalue be ?
- Else,
- Letrhs be ?
Evaluation ofInitializer . - Letvalue be ?
GetValue (rhs).
- Letrhs be ?
- Perform ?
PutValue (lhs,value). - LetkeyResult be ?
ForIn/OfHeadEvaluation (« »,Expression ,enumerate ). - Return ?
ForIn/OfBodyEvaluation (BindingIdentifier ,Statement ,keyResult,enumerate ,var-binding ,labelSet).
B.3.6 The[[IsHTMLDDA]] Internal Slot
An[[IsHTMLDDA]] internal slot may exist ontypeof operator
Objects with an[[IsHTMLDDA]] internal slot are never created by this specification. However, thedocument.all object in web browsers is adocument.all.
B.3.6.1 Changes to ToBoolean
The following step replaces step
- Ifargument
is an Object andargument has an[[IsHTMLDDA]] internal slot, returnfalse .
B.3.6.2 Changes to IsLooselyEqual
The following steps replace step
- Perform the following steps:
- Ifx
is an Object ,x has an[[IsHTMLDDA]] internal slot, andy is eitherundefined ornull , returntrue . - Ifx is either
undefined ornull ,yis an Object , andy has an[[IsHTMLDDA]] internal slot, returntrue .
- Ifx
B.3.6.3 Changes to thetypeof Operator
The following step replaces steptypeof
- Ifval has an[[IsHTMLDDA]] internal slot, return
"undefined" .
B.3.7 Non-default behaviour in HostMakeJobCallback
The
B.3.8 Non-default behaviour in HostEnsureCanAddPrivateElement
The
C The Strict Mode of ECMAScript
The strict mode restriction and exceptions
implements,interface,let,package,private,protected,public,static, andyieldarereserved words withinstrict mode code . (12.7.2 ).- A conforming implementation, when processing
strict mode code , must disallow instances of the productionsNumericLiteral :: LegacyOctalIntegerLiteral DecimalIntegerLiteral :: NonOctalDecimalIntegerLiteral - A conforming implementation, when processing
strict mode code , must disallow instances of the productionsEscapeSequence :: LegacyOctalEscapeSequence EscapeSequence :: NonOctalDecimalEscapeSequence - Assignment to an undeclared identifier or otherwise unresolvable reference does not create a property in the
global object . When a simple assignment occurs withinstrict mode code , itsLeftHandSideExpression must not evaluate to an unresolvable Reference. If it does aReferenceError exception is thrown (6.2.5.6 ). TheLeftHandSideExpression also may not be a reference to adata property with the attribute value {[[Writable]]:false }, to anaccessor property with the attribute value {[[Set]]:undefined }, nor to a non-existent property of an object whose[[Extensible]] internal slot isfalse . In these cases aTypeErrorexception is thrown (13.15 ). - An
IdentifierReference with theStringValue "eval" or"arguments" may not appear as theLeftHandSideExpression of an Assignment operator (13.15 ) or of anUpdateExpression (13.4 ) or as theUnaryExpression operated upon by a Prefix Increment (13.4.4 ) or a Prefix Decrement (13.4.5 ) operator. - Arguments objects for
strict functions define a non-configurableaccessor property "callee" which throws aTypeError exception on access (10.4.4.6 ). - Arguments objects for
strict functions do not dynamically share theirarray-indexed property values with the corresponding formal parameter bindings of their functions. (10.4.4 ). - For
strict functions , if an arguments object is created the binding of the local identifierargumentsto the arguments object is immutable and hence may not be the target of an assignment expression. (10.2.11 ). - It is a
SyntaxError if theStringValue of aBindingIdentifier is either"eval" or"arguments" withinstrict mode code (13.1.1 ). - Strict mode eval code cannot instantiate variables or functions in the variable environment of the caller to eval. Instead, a new variable environment is created and that environment is used for declaration binding instantiation for the eval code (
19.2.1 ). - If
this is evaluated withinstrict mode code , then thethis value is not coerced to an object. Athis value of eitherundefined ornull is not converted to theglobal object and primitive values are not converted to wrapper objects. Thethis value passed via a function call (including calls made usingFunction.prototype.applyandFunction.prototype.call) do not coerce the passedthis value to an object (10.2.1.2 ,20.2.3.1 ,20.2.3.3 ). - When a
deleteoperator occurs withinstrict mode code , aSyntaxError is thrown if itsUnaryExpression is a direct reference to a variable, function argument, or function name (13.5.1.1 ). - When a
deleteoperator occurs withinstrict mode code , aTypeError is thrown if the property to be deleted has the attribute {[[Configurable]]:false } or otherwise cannot be deleted (13.5.1.2 ). Strict mode code may not include aWithStatement . The occurrence of aWithStatement in such a context is aSyntaxError (14.11.1 ).- It is a
SyntaxError if aCatchParameter occurs withinstrict mode code andBoundNames ofCatchParameter contains eitherevalorarguments(14.15.1 ). - It is a
SyntaxError if the sameBindingIdentifier appears more than once in theFormalParameters of astrict function . An attempt to create such a function using a Function, Generator, or AsyncFunctionconstructor is aSyntaxError (15.2.1 ,20.2.1.1.1 ). - An implementation may not extend, beyond that defined in this specification, the meanings within
strict functions of properties named"caller" or"arguments" of function instances.
D Host Layering Points
See
D.1 Host Hooks
D.2 Host-defined Fields
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostDefined]] on
[[HostSynchronizesWith]] on Candidate Executions: See
[[IsHTMLDDA]]: See
D.3 Host-defined Objects
The
D.4 Running Jobs
Preparation steps before, and cleanup steps after, invocation of
D.5 Internal Methods of Exotic Objects
Any of the essential internal methods in
D.6 Built-in Objects and Methods
Any built-in objects and methods not defined within this specification, except as restricted in
E Corrections and Clarifications in ECMAScript 2015 with Possible Compatibility Impact
Date.prototype.toString when the
/.
String.prototype.match andString.prototype.replace was incorrect for cases where the pattern argument was a RegExp value whoseglobal flag is set. The previous specifications stated that for each attempt to match the pattern, iflastIndex did not change, it should be incremented by 1. The correct behaviour is thatlastIndex should be incremented by 1 only if the pattern matched the empty String.
Array.prototype.sort. ECMAScript 2015 specifies that such as value is treated as if
F Additions and Changes That Introduce Incompatibilities with Prior Editions
Space_Separator (Zs) category and thus treated as whitespace in ECMAScript 2015, to be moved to theFormat (Cf) category (as of Unicode 6.3.0). This causes whitespace-sensitive methods to behave differently. For example,"\u180E".trim().length was0 in previous editions, but1 in ECMAScript 2016 and later. Additionally, ECMAScript 2017 mandated always using the latest version of the Unicode Standard.
let followed by the token[ is the start of a
( token of a for statement is immediately followed by the token sequencelet [ then thelet is treated as the start of a
let [ then thelet is treated as the start of a
in
var declaration for the same
eval whose eval code includes avar orFunctionDeclaration declaration that binds the same
Object.freeze is not an object it is treated as if it was a non-extensible
Object.getOwnPropertyDescriptor is not an object an attempt is made to coerce the argument using
Object.getOwnPropertyNames is not an object an attempt is made to coerce the argument using
Object.getPrototypeOf is not an object an attempt is made to coerce the argument using
Object.isExtensible is not an object it is treated as if it was a non-extensible
Object.isFrozen is not an object it is treated as if it was a non-extensible
Object.isSealed is not an object it is treated as if it was a non-extensible
Object.keys is not an object an attempt is made to coerce the argument using
Object.preventExtensions is not an object it is treated as if it was a non-extensible
Object.seal is not an object it is treated as if it was a non-extensible
String.prototype.localeCompare function must treat Strings that are canonically equivalent according to the Unicode Standard as being identical. In previous editions implementations were permitted to ignore canonical equivalence and could instead use a bit-wise comparison.
String.prototype.trim method is defined to recognize white space code points that may exist outside of the Unicode BMP. However, as of Unicode 7 no such code points are defined. In previous editions such code points would not have been recognized as white space.
Atomics.wake has been renamed toAtomics.notify to prevent confusion withAtomics.wait.
await was reduced, which could create an observable difference in resolution order between athen() call and anawait expression.
G Colophon
This specification is authored onGitHub in a plaintext source format calledEcmarkup. Ecmarkup is an HTML and Markdown dialect that provides a framework and toolset for authoring ECMAScript specifications in plaintext and processing the specification into a full-featured HTML rendering that follows the editorial conventions for this document. Ecmarkup builds on and integrates a number of other formats and technologies includingGrammarkdown for defining syntax andEcmarkdown for authoring algorithm steps. PDF renderings of this specification are produced by printing the HTML rendering to a PDF.
Prior editions of this specification were authored using Word—the Ecmarkup source text that formed the basis of this edition was produced by converting the ECMAScript 2015 Word document to Ecmarkup using an automated conversion tool.
H Bibliography
- IEEE 754-2019:IEEE Standard for Floating-Point Arithmetic. Institute of Electrical and Electronic Engineers, New York (2019)
Note There are no normative changes between IEEE 754-2008 and IEEE 754-2019 that affect the ECMA-262 specification.
- The Unicode Standard, available at <https://unicode.org/versions/latest>
- Unicode Technical Note #5: Canonical Equivalence in Applications, available at <https://unicode.org/notes/tn5/>
- Unicode Technical Standard #10: Unicode Collation Algorithm, available at <https://unicode.org/reports/tr10/>
- Unicode Standard Annex #15, Unicode Normalization Forms, available at <https://unicode.org/reports/tr15/>
- Unicode Standard Annex #18: Unicode Regular Expressions, available at <https://unicode.org/reports/tr18/>
- Unicode Standard Annex #24: Unicode
ScriptProperty, available at <https://unicode.org/reports/tr24/> - Unicode Standard Annex #31, Unicode Identifiers and Pattern Syntax, available at <https://unicode.org/reports/tr31/>
- Unicode Standard Annex #44: Unicode Character Database, available at <https://unicode.org/reports/tr44/>
- Unicode Technical Standard #51: Unicode Emoji, available at <https://unicode.org/reports/tr51/>
- IANA Time Zone Database, available at <https://www.iana.org/time-zones>
- ISO 8601:2004(E)Data elements and interchange formats — Information interchange — Representation of dates and times
- RFC 1738 “Uniform Resource Locators (URL)”, available at <https://tools.ietf.org/html/rfc1738>
- RFC 2396 “Uniform Resource Identifiers (URI): Generic Syntax”, available at <https://tools.ietf.org/html/rfc2396>
- RFC 3629 “UTF-8, a transformation format of ISO 10646”, available at <https://tools.ietf.org/html/rfc3629>
- RFC 7231 “Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content”, available at <https://tools.ietf.org/html/rfc7231>
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