Web/JavaScript/Reference/Global objects/Symbol/iterator

The well-known Symbol.iterator symbol specifies the default iterator for an object. Used by for...of.

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Description

Whenever an object needs to be iterated (such as at the beginning of a for..of loop), its @@iterator method is called with no arguments, and the returned iterator is used to obtain the values to be iterated.

Some built-in types have a default iteration behavior, while other types (such as Object) do not. The built-in types with a @@iterator method are:

See also Iteration protocols for more information.

Property attributes of `Symbol.iterator`
Writable	no
Enumerable	no
Configurable	no

Examples

User-defined iterables

We can make our own iterables like this:

var myIterable = {}
myIterable[Symbol.iterator] = function* () {
    yield 1;
    yield 2;
    yield 3;
};
[...myIterable] // [1, 2, 3]

Or iterables can be defined directly inside a class or object using a computed property:

class Foo {
  *[Symbol.iterator] () {
    yield 1;
    yield 2;
    yield 3;
  }
}

const someObj = {
  *[Symbol.iterator] () {
    yield 'a';
    yield 'b';
  }
}

[...new Foo] // [ 1, 2, 3 ]
[...someObj] // [ 'a', 'b' ]

Non-well-formed iterables

If an iterable's @@iterator method does not return an iterator object, then it is a non-well-formed iterable. Using it as such is likely to result in runtime exceptions or buggy behavior:

var nonWellFormedIterable = {}
nonWellFormedIterable[Symbol.iterator] = () => 1
[...nonWellFormedIterable] // TypeError: [] is not a function

Specifications

Specification
ECMAScript (ECMA-262)The definition of 'Symbol.iterator' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`iterator`	Chrome Full support 43	Edge Full support 12	Firefox Full support 36	IE No support No	Opera Full support 30	Safari Full support 10	WebView Android Full support 43	Chrome Android Full support 43	Firefox Android Full support 36	Opera Android Full support 30	Safari iOS Full support 10	Samsung Internet Android Full support 4.0	nodejs Full support 0.12

Legend

Full support: Full support
No support: No support