The structured clone algorithm

Thestructured clone algorithm copies complex JavaScript objects.It is used internally when invoking structuredClone(), to transfer data betweenWorkers viapostMessage(), storing objects withIndexedDB, or copying objects forother APIs.

It clones by recursing through the input object while maintaining a map of previously visited references, to avoid infinitely traversing cycles.

Things that don't work with structured clone

Function objects cannot be duplicated by the structured clone algorithm; attempting to throws aDataCloneError exception.
Cloning DOM nodes likewise throws aDataCloneError exception.
Certain object properties are not preserved:
- ThelastIndex property ofRegExp objects is not preserved.
- Property descriptors, setters, getters, and similar metadata-like features are not duplicated.For example, if an object is marked readonly with aproperty descriptor, it will be read/write in the duplicate, since that's the default.
- The prototype chain is not walked or duplicated.
- Class private elements are not duplicated. (Although internal fields of built-in types may.)

Supported types

JavaScript types

Array
ArrayBuffer
Boolean
DataView
Date
Error types (but seeError types below).
Map
Number
Object objects: but only plain objects (e.g., from object literals).
Primitive types, exceptsymbol.
RegExp: but note thatlastIndex is not preserved.
Set
String
TypedArray

Error types

ForError types, the error name must be one of:Error,EvalError,RangeError,ReferenceError,SyntaxError,TypeError,URIError (or will be set to "Error").

Browsers must serialize the propertiesname andmessage, and are expected to serialize other "interesting" properties of the errors such asstack,cause, etc.

AggregateError support is expected to be added to the specification inwhatwg/html#5749 (and is already supported in some browsers).