JavaScript .keys()

The .keys() method returns a new array iterator object containing the keys (indices) for each index in the array.

Syntax

array.keys();

Parameters:

• This method does not take any parameters.

Return value:

• A new array iterator object containing the keys (indices) of the array.

Example 1: Using .keys() to Get Array Indices

In this example, the .keys() method creates an iterator over the indices of the array:

const cats = ['Sundae', 'Gandalf', 'Campanita'];
const catsIterator = cats.keys();

for (const cat of catsIterator) {
  console.log(cat);
}

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Here is the output:

0
1
2

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Example 2: Converting the .keys() Iterator to an Array

In this example, the spread operator (...) with .keys() is used to convert the index iterator into a full array of indices:

const colors = ['red', 'black', 'white'];
const indices = [...colors.keys()];

console.log('Array indices: ', indices);
console.log('First index: ', indices[0]);

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Here is the output:

Array indices:  [0, 1, 2]
First index:  0

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Codebyte Example: Using .keys() with Sparse Arrays

In this codebyte example, .keys() is used on a sparse array. Even though some elements are missing, .keys() still returns all valid indices:

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