TheSymbol.iterator static data property represents thewell-known symbolSymbol.iterator. Theiterable protocol looks up this symbol for the method that returns the iterator for an object. In order for an object to be iterable, it must have a[Symbol.iterator] key.

Try it

const iterable = {};iterable[Symbol.iterator] = function* () {  yield 1;  yield 2;  yield 3;};console.log([...iterable]);// Expected output: Array [1, 2, 3]

Value

The well-known symbolSymbol.iterator.

Description

Whenever an object needs to be iterated (such as at the beginning of afor...of loop), its[Symbol.iterator]() method is called with no arguments, and the returnediterator is used to obtain the values to be iterated.

Some built-in types have a default iteration behavior, while other types (such asObject) do not. Some built-in types with a[Symbol.iterator]() method are:

• Array.prototype[Symbol.iterator]()
• TypedArray.prototype[Symbol.iterator]()
• String.prototype[Symbol.iterator]()
• Map.prototype[Symbol.iterator]()
• Set.prototype[Symbol.iterator]()

See alsoIteration protocols for more information.

Examples

User-defined iterables

We can make our own iterables like this:

const 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 acomputed property:

class Foo {  *[Symbol.iterator]() {    yield 1;    yield 2;    yield 3;  }}const someObj = {  *[Symbol.iterator]() {    yield "a";    yield "b";  },};console.log(...new Foo()); // 1, 2, 3console.log(...someObj); // 'a', 'b'

Non-well-formed iterables

If an iterable's[Symbol.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:

const nonWellFormedIterable = {};nonWellFormedIterable[Symbol.iterator] = () => 1;[...nonWellFormedIterable]; // TypeError: [Symbol.iterator]() returned a non-object value

Specifications

Browser compatibility

See also

• Polyfill ofSymbol.iterator incore-js
• Iteration protocols
• Array.prototype[Symbol.iterator]()
• TypedArray.prototype[Symbol.iterator]()
• String.prototype[Symbol.iterator]()
• Map.prototype[Symbol.iterator]()
• Set.prototype[Symbol.iterator]()
• arguments[Symbol.iterator]()
• Segments.prototype[Symbol.iterator]()