Primitive types use a fixed format; some can contain only a limited number of certain values. In contrast, objects are more complex, especially including methods and properties.
With the exception ofnull andundefined, primitive types have a correspondingobject wrapper with data type specific methods. Therefore you will find on this page descriptions of some methods.
String is a datatype to hold text of arbitrary length. String variables are created by assigning a string literal to them. String literals can be enclosed in" " or' '.
"use strict";constmyName_1="Mike";// double quoteconstmyName_2='Monica';// apostropheconstmyName_3="naɺ̠ɯçito";// non-latin characters
If your string literal contains a" or', you can use the other one as the outer delimiter, or you escape them with a\ .
"use strict";constbook_1="Mike's book";constmonica_1='Here name is "Monica".';constbook_2='Mike\'s book';constmonica_2="Here name is \"Monica\".";
If your string literal is computed out of some fixed text plus some dynamic parts, you can use thetemplate literal technique. Here, the literal is enclosed in backticks` ` and contains variables and expressions.
"use strict";consta=1;constb=2;constresultMessage=`The sum of${a} and${b} is:${a+b}.`;// same as:'The sum of '+a+' and '+b+' is: '+(a+b);alert(resultMessage);
The+ operator concatenates two strings, e.g.alert("Hello " + "world!");. Additionally, there are a lot ofmethods for strings.
Hint: JavaScript doesn't have something like a 'character' or 'byte' data type.
We show some methods which are often used. For a complete list, please refer toMDN.
length is a property, not a method. Hence there are no parenthesizes(). It returns the length of the string as a whole number.
constfoo="Hello!";alert(foo.length);// 6
The method returnstrue if the string contains a specified string, otherwise it returnsfalse.
lettext="Hello world, hello Wikiversity!";document.write(text.includes("Hello"));//true
The method returns a string where 'text' is appended to the original string.
constfoo="Hello";constbar=foo.concat(" World!");alert(bar);// Hello World!
The method returns the position of the first occurrence of 'searchText', starting with 0. If 'searchText' cannot be found, -1 is returned. The method acts case sensitive.
constfoo="Hello, World! How do you do?";alert(foo.indexOf(" "));// 6consthello="Hello world, welcome to the universe.";alert(hello.indexOf("welcome"));// 13
The method compares the string with a regular expression (=pattern), returning the index of the first match in the string. It is similar toindexOf(), but much more powerful. E.g.: it can be made case insensitive by replacing the quotation marks in"hello" with forward slashes and ani at the end.
lettext="Hello world, hello Wikiversity!";document.write(text.search(/hello/i));// 0
The method returns the position of the last occurrence of 'searchText'. If 'searchText' cannot be found, -1 is returned. The method acts case sensitive.
constfoo="Hello, World! How do you do?";alert(foo.lastIndexOf(' '));// 24
The method returns a string where 'text' is replaced by 'NewText' on the original string. Only the first occurrence is replaced. The method acts case sensitive.
constfoo="foo bar foo bar foo";constnewString=foo.replace("bar","NEW"):alert(foo);// foo bar foo bar fooalert(newString);// foo NEW foo bar foo
As you can see, thereplace method only returns the new content and does not modify the origin string in 'foo'.
The method returns a substring beginning at the 'start' position.
"hello".slice(1);// "ello"
When the 'end' is provided, they are extracted up to, but not including the end position.
"hello".slice(1,3);// "el"
slice allows extracting text referenced from the end of the string by using negative indexing.
"hello".slice(-4,-2);// "el"
Unlikesubstring, the slice method never swaps the 'start' and 'end' positions. If the 'start' is after the 'end',slice will attempt to extract the content as presented, but will most likely provide unexpected results.
"hello".slice(3,1);// ""
The method isdeprecated. Usesubstring orslice instead.
The method extracts a substring starting at the 'start' position.
"hello".substring(1);// "ello"
When the 'end' is provided, they are extracted up to, but not including the end position.
"hello".substring(1,3);// "el"
substring always works from left to right. If the 'start' position is larger than the 'end' position,substring will swap the values; although sometimes useful, this is not always what you want; different behavior is provided byslice.
"hello".substring(3,1);// "el"
The method returns the current string in lower case.
constfoo="Hello!";alert(foo.toLowerCase());// hello!
The method returns the current string in upper case.
constfoo="Hello!";alert(foo.toUpperCase());// HELLO!
Number is one of the two numeric types (the other one isBigInt).Number stores integer values as well as floating point values in a unified 64-bit format defined byIEEE 754. That means, that JavaScript doesn't have different data types for integers and float like some other languages.
The possible range for such values is approximate -10300 to +10300 with different precision depending on the distance to 0.
In the range from -(253 − 1) to +253 − 1 there is no uncertainness for integer operations. 253 = 9,007,199,254,740,992 which is a little smaller than 1016.
"use strict";letcounter=20;// no decimal pointalert(counter+" "+typeofcounter);letdegree=12.1;// with decimal pointalert(degree+" "+typeofdegree);
ForNumber the usual arithmetic operators ('power' is** and 'modulo' is%), comparison operators (<,>, ...), and bitwise operators are available.
In opposite to some other languages, the division of two whole numbers can result in a number with decimal places, e.g.alert(1/3);.
Working with numbers is supported by many properties and methods. Internally, they are implemented at different areas:
Math provides properties that represent common mathematical constants likeπ ore. Syntax:Math.xyz (no parenthesis)Math provides common mathematical functions likesin orlog. Syntax:Math.xyz() (with parenthesis)Number provides properties that characterize the implementation of the data type number, likeMAX_VALUE orNEGATIVE_INFINITY. Syntax:Number.xyz (no parenthesis)Number providesstatic methods that check the relation between numbers and other data types, e.g.,isInteger orparseFloat. Syntax:Number.xyz() (with parenthesis)Number providesinstance methods that act on concrete number values or variables, e.g.,toExponential ortoFixed. Syntax:value.xyz() (with parenthesis)// some examples"use strict";constvar_1=Math.PI;alert(var_1);alert(var_1.toFixed(2));constvar_2=Math.sqrt(3);alert(var_2);alert(Number.MAX_VALUE);alert(Number.isInteger(123));// truealert(Number.isInteger(12.3));// false
We show some properties and methods which are often used. For a complete list, please refer toMDN Math andMDN Numbers.
Most commonly used constants:
Math.E Returns the constant e.Math.PI Returns the constant pi.Math.LN10 Returns the natural logarithm of 10.Math.LN2 Returns the natural logarithm of 2.Math.SQRT2 Returns the square root of 2.Returns thesmallest integer greater than the number passed as an argument.
constmyInt=Math.ceil(90.8);alert(myInt);// 91alert(Math.ceil(-90.8));// -90
Returns thegreatest integer less than the number passed as an argument.
constmyInt=Math.floor(90.8);alert(myInt);// 90alert(Math.floor(-90.8));// -91
Returns theclosest integer to the number passed as an argument.
alert(Math.round(90.8));// 91alert(Math.round(-90.8));// -91alert(Math.round(90.3));// 90alert(Math.round(-90.3));// -90
Returns the higher number from the two numbers passed as arguments.
alert(Math.max(8.3,9));// 9alert(Math.max(8.3,-9));// 8.3
Returns the lower number from the two numbers passed as arguments.
alert(Math.min(8.3,9));// 8.3alert(Math.min(8.3,-9));// -9
Generates a pseudo-random number between 0 and 1.
alert(Math.random());
The two methodsparseInt andparseFloat convert strings into numbers. They scan the given string from left to right. When they recognize a character distinct from 0 - 9, they finish scanning and return the converted numbers read so far (parseFloat accepts the decimal point). If the first character is distinct from 0 - 9, they returnMath.NaN, meaningNot a Number.
Hint: It's not necessary to specify 'Number.' in the source code.
constx=parseInt("7.5");alert(x);// 7consty=parseInt("Five");alert(y);// NaNconstz=parseFloat("2.8")+3;alert(z);// 5.8// scientific notation is acceptedalert(parseFloat("123.456e6"));// 123456000
BigInt is a data type that representsintegers ofarbitrary length. Hence, it's a variable-length format (conceptually) delimited only by the available RAM.
BigInts are created either by adding a 'n' to the end of an integer literal or by using theBigInt() function.
"use strict";lethugeNumber_1=12345678901234567890n;// 'n' at the endalert(typeofhugeNumber_1);lethugeNumber_2=BigInt("12345678901234567890");// no 'n'alert(typeofhugeNumber_2);// a 'small' BigInt can be created out of an integer valuelethugeNumber_3=BigInt(123);alert(typeofhugeNumber_3);
BigInt supports the arithmetic operators+ - * / **, comparison operators, and most of the bitwise operators.
Boolean variables can contain one of two possible values,true orfalse. JavaScript representsfalse by either a Boolean false, the number 0, NaN, an empty string, or the built-in types undefined or null. Any other values are treated astrue.
"use strict";letfirstLoop=true;alert(typeoffirstLoop);
Variables that have just been declared but not initialized with any value have the data typeundefined.
"use strict";letx;// ...alert(typeofx);if(x==undefined){// remedy the missing initializationx=0;}alert(typeofx);// ...
In JavaScript,null is marked as one of the primitive values, because its behavior is seemingly primitive. However, when using thetypeof operator, it returns "object". This is considered a bug, but one which cannot be fixed because it will break too many scripts.[1]
Symbol represents aunique identifier.Symbols may have a descriptor that is given as a string to its constructor.
"use strict";// 'person' is a symbol with the description "Olaf"constperson=Symbol("Olaf");alert(person.description);// Olaf
Symbols are used as keys in objects (embedded in[ ]) to guarantee uniqueness.
ECMAScript definitions on data types