Array.prototype[@@iterator]()

The [@@iterator]() method of Array instances implements the iterable protocol and allows arrays to be consumed by most syntaxes expecting iterables, such as the spread syntax and for...of loops. It returns an array iterator object that yields the value of each index in the array.

The initial value of this property is the same function object as the initial value of the Array.prototype.values property.

Syntax

js

array[Symbol.iterator]()

Return value

The same return value as Array.prototype.values(): a new iterable iterator object that yields the value of each index in the array.

Examples

Iteration using for...of loop

Note that you seldom need to call this method directly. The existence of the @@iterator method makes arrays iterable, and iterating syntaxes like the for...of loop automatically calls this method to obtain the iterator to loop over.

HTML

html

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

JavaScript

js

const arr = ["a", "b", "c"];
const letterResult = document.getElementById("letterResult");
for (const letter of arr) {
  const li = document.createElement("li");
  li.textContent = letter;
  letterResult.appendChild(li);
}

Result

Manually hand-rolling the iterator

You may still manually call the next() method of the returned iterator object to achieve maximum control over the iteration process.

js

const arr = ["a", "b", "c", "d", "e"];
const arrIter = arr[Symbol.iterator]();
console.log(arrIter.next().value); // a
console.log(arrIter.next().value); // b
console.log(arrIter.next().value); // c
console.log(arrIter.next().value); // d
console.log(arrIter.next().value); // e

Handling strings and string arrays with the same function

Because both strings and arrays implement the iterable protocol, a generic function can be designed to handle both inputs in the same fashion. This is better than calling Array.prototype.values() directly, which requires the input to be an array, or at least an object with such a method.

js

function logIterable(it) {
  if (typeof it[Symbol.iterator] !== "function") {
    console.log(it, "is not iterable.");
    return;
  }
  for (const letter of it) {
    console.log(letter);
  }
}

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

// String
logIterable("abc");
// a
// b
// c

// Number
logIterable(123);
// 123 is not iterable.

Specifications

Specification
ECMAScript Language Specification
# sec-array.prototype-@@iterator

Browser compatibility

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See also