Array.prototype.entries()

{{JSRef}}

The entries() method of {{jsxref("Array")}} instances returns a new array iterator object that contains the key/value pairs for each index in the array.

{{InteractiveExample("JavaScript Demo: Array.entries()")}}

const array1 = ["a", "b", "c"];

const iterator1 = array1.entries();

console.log(iterator1.next().value);
// Expected output: Array [0, "a"]

console.log(iterator1.next().value);
// Expected output: Array [1, "b"]

Syntax

entries()

Parameters

None.

Return value

A new iterable iterator object.

Description

When used on sparse arrays, the entries() method iterates empty slots as if they have the value undefined.

The entries() method is generic. It only expects the this value to have a length property and integer-keyed properties.

Examples

Iterating with index and element

const a = ["a", "b", "c"];

for (const [index, element] of a.entries()) {
  console.log(index, element);
}

// 0 'a'
// 1 'b'
// 2 'c'

Using a for…of loop

const array = ["a", "b", "c"];
const arrayEntries = array.entries();

for (const element of arrayEntries) {
  console.log(element);
}

// [0, 'a']
// [1, 'b']
// [2, 'c']

Iterating sparse arrays

entries() will visit empty slots as if they are undefined.

for (const element of [, "a"].entries()) {
  console.log(element);
}
// [0, undefined]
// [1, 'a']

Calling entries() on non-array objects

The entries() method reads the length property of this and then accesses each property whose key is a nonnegative integer less than length.

const arrayLike = {
  length: 3,
  0: "a",
  1: "b",
  2: "c",
  3: "d", // ignored by entries() since length is 3
};
for (const entry of Array.prototype.entries.call(arrayLike)) {
  console.log(entry);
}
// [ 0, 'a' ]
// [ 1, 'b' ]
// [ 2, 'c' ]

Specifications

{{Specifications}}

Browser compatibility

{{Compat}}

docs.rodeo

MDN Web Docs mirror