Array.prototype[@@iterator]()

The @@iterator method is part of The iterable protocol, that defines how to synchronously iterate over a sequence of values.

The initial value of the @@iterator property is the same function object as the initial value of the values() property.

Syntax

arr[Symbol.iterator]()

Return value

The initial value given by the values() iterator. By default, using arr[Symbol.iterator] will return the values() function.

Examples

Iteration using for...of loop

HTML

<ul id="letterResult">
</ul>

JavaScript

var arr = ['a', 'b', 'c'];
var eArr = arr[Symbol.iterator]();
var letterResult = document.getElementById('letterResult');
// your browser must support for..of loop
// and let-scoped variables in for loops
// const and var could also be used
for (let letter of eArr) {
 letterResult.innerHTML += "<li>" + letter + "</li>";
}

Result

Alternative iteration

var arr = ['a', 'b', 'c', 'd', 'e'];
var eArr = arr[Symbol.iterator]();
console.log(eArr.next().value); // a
console.log(eArr.next().value); // b
console.log(eArr.next().value); // c
console.log(eArr.next().value); // d
console.log(eArr.next().value); // e

Use Case for brace notation

The use case for this syntax over using the dot notation (Array.prototype.values()) is in a case where you don't know what object is going to be ahead of time. If you have a function that takes an iterator and then iterate over the value, but don't know if that Object is going to have a [Iterable].prototype.values method. This could be a built-in object like String object or a custom object.

function logIterable(it) {
 if (!(Symbol.iterator in Object.getPrototypeOf(it)
 /* or "Symbol.iterator in Object.__proto__"
    or "it[Symbol.iterator]" */)) {
   console.log(it, ' is not an iterable object...');
   return;
 }

 var iterator = it[Symbol.iterator]();
  // your browser must support for..of loop
  // and let-scoped variables in for loops
  // const and var could also be used
  for (let letter of iterator) {
      console.log(letter);
  }
}

// Array
logIterable(['a', 'b', 'c']);
// a
// b
// c

// string
logIterable('abc');
// a
// b
// c

logIterable(123);
// 123 " is not an iterable object..."

Specifications

Specification
ECMAScript (ECMA-262)
The definition of 'Array.prototype[@@iterator]()' in that specification.

Browser compatibility

DesktopMobileServer
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung InternetNode.js
@@iteratorChrome Full support 38Edge Full support 12Firefox Full support 36
Full support 36
No support 27 — 36
Notes Alternate Name
Notes A placeholder property named @@iterator is used.
Alternate Name Uses the non-standard name: @@iterator
No support 17 — 27
Notes Alternate Name
Notes A placeholder property named iterator is used.
Alternate Name Uses the non-standard name: iterator
IE No support NoOpera Full support 25Safari Full support 10WebView Android Full support 38Chrome Android Full support 38Firefox Android Full support 36
Full support 36
No support 27 — 36
Notes Alternate Name
Notes A placeholder property named @@iterator is used.
Alternate Name Uses the non-standard name: @@iterator
No support 17 — 27
Notes Alternate Name
Notes A placeholder property named iterator is used.
Alternate Name Uses the non-standard name: iterator
Opera Android Full support 25Safari iOS Full support 10Samsung Internet Android Full support 3.0nodejs Full support 0.12

Legend

Full support
Full support
No support
No support
See implementation notes.
See implementation notes.
Uses a non-standard name.
Uses a non-standard name.

See also