The well-known Symbol.iterator
symbol specifies the default iterator for an object. Used by for...of
.
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 |
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' ]
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
Desktop | ||||||
---|---|---|---|---|---|---|
iterator |
43 | 12 | 36 | No | 30 | 10 |
Mobile | ||||||
---|---|---|---|---|---|---|
iterator |
43 | 43 | 36 | 30 | 10 | 4.0 |
Server | |
---|---|
iterator |
0.12 |
Array.prototype[@@iterator]()
TypedArray.prototype[@@iterator]()
String.prototype[@@iterator]()
Map.prototype[@@iterator]()
Set.prototype[@@iterator]()
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Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://wiki.developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol/iterator