Symbol.iterator
The Symbol.iterator
well-known symbol specifies the default iterator for an object. Used by for...of
.
Property attributes of Symbol.iterator |
|
---|---|
Writable | no |
Enumerable | no |
Configurable | no |
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:
Array.prototype[@@iterator]()
TypedArray.prototype[@@iterator]()
String.prototype[@@iterator]()
Map.prototype[@@iterator]()
Set.prototype[@@iterator]()
See also Iteration protocols for more information.
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]
Non-well-formed iterables
If an iterable's @@iterator
method doesn't return an iterator object, then it's 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 | Status | Comment |
---|---|---|
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Symbol.iterator' in that specification. |
Standard | Initial definition. |
ECMAScript 2017 Draft (ECMA-262) The definition of 'Symbol.iterator' in that specification. |
Draft |
Browser compatibility
Feature | Chrome | Firefox (Gecko) | Internet Explorer | Opera | Safari |
---|---|---|---|---|---|
Basic support | 43 | 36 (36) | No support | 30 | No support |
Feature | Android | Chrome for Android | Firefox Mobile (Gecko) | IE Mobile | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|
Basic support | No support | No support | 36.0 (36) | No support | No support | No support |
See also
- Iteration protocols
Array.prototype[@@iterator]()
TypedArray.prototype[@@iterator]()
String.prototype[@@iterator]()
Map.prototype[@@iterator]()
Set.prototype[@@iterator]()
License
© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/javascript/reference/global_objects/symbol/iterator