JavaScript Array keys() Method

JavaScript Array keys() method returns a new Array Iterator object containing the keys (or indices) of the elements in the array. It is particularly useful for iterating over an array’s indices.

Pre-requisites to Learn

JavaScript Array

Syntax

arr.keys();

Parameters

The Array.keys() method does not accept any parameters.

Return Value

The keys() method returns a new Array Iterator object that contains the indices (keys) of the array elements. The iterator can be used in loops or converted into an array.

Notes:

This method does not modify the original array.
This method returns the indices of the array.

Examples of JavaScript Array keys() Method

Example 1: The keys() method returns an iterator that can be used to loop through the indices of the array.

let arr = ['apple', 'banana', 'cherry'];

let keysIterator = fruits.keys();

for (let key of keysIterator) {
    console.log(key);
}
// Output:
// 0
// 1
// 2

Example 2: This method combined with Array.from() method to create an array of indices.

let arr = [10, 20, 30, 40];

let keysArray = Array.from(arr.keys());
console.log(keysArray); // Output: [0, 1, 2, 3]

Example 3: Using keys() with Sparse Arrays – the second element is missing, its index (1) is still included in the keys.

let sparseArray = [10, , 30, 40];

let keysIterator = sparseArray.keys();

for (let key of keysIterator) {
  console.log(key);
}
// Output:
// 0
// 1
// 2
// 3

Example 4: The keys() method can be combined with map() or other methods for advanced processing.

let arr = ['apple', 'banana', 'cherry'];

let keyValues = arr.keys();
let result = Array.from(keyValues).map(key => `Index: ${key}`);

console.log(result); // Output: ['Index: 0', 'Index: 1', 'Index: 2']

Supported Browsers

Browser	Support
Chrome	38+
Firefox	32+
Safari	8+
Edge	12+
Opera	25+
Internet Explorer	Not supported

Comparison with Other Methods

Method	Purpose
Array.keys() Method	Returns an iterator of array indices (keys).
Array.values() Method	Returns an iterator of array values.
Array.entries() Method	Returns an iterator of [index, value] pairs.