The well-known Symbol.iterator
symbol specifies the default iterator for an object. Used by for...of
.
Symbol.iterator
Try it
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.
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'; } } console.log(...new Foo); // 1, 2, 3 console.log(...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 Language Specification # sec-symbol.iterator |
Browser compatibility
Desktop | Mobile | Server | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
iterator |
43
|
12
|
36
|
No
|
30
|
10
|
43
|
43
|
36
|
30
|
10
|
4.0
|
1.0
|
0.12.0
|
See also
© 2005–2022 MDN 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