How to Use Entries and Keys in Array in JavaScript

In JavaScript, use array.entries() to get an iterator of [index, value] pairs, and array.keys() to get an iterator of indexes only. These methods help you loop through arrays when you need both positions and elements or just the positions.

Syntax

array.entries() returns an iterator with [index, value] pairs for each element in the array.

array.keys() returns an iterator with the indexes (keys) of the array elements.

You can use these iterators with for...of loops to access array data.

javascript

const array = ['a', 'b', 'c'];

const entriesIterator = array.entries();
const keysIterator = array.keys();

Example

This example shows how to use entries() to get index and value pairs, and keys() to get only indexes from an array.

javascript

const fruits = ['apple', 'banana', 'cherry'];

console.log('Using entries():');
for (const [index, fruit] of fruits.entries()) {
  console.log(index, fruit);
}

console.log('Using keys():');
for (const index of fruits.keys()) {
  console.log(index);
}

Output

Using entries():
0 apple
1 banana
2 cherry
Using keys():
0
1
2

Common Pitfalls

One common mistake is trying to use entries() or keys() directly as arrays without iterating. These methods return iterators, not arrays.

Also, using forEach with entries() won't work directly because entries() returns an iterator, not an array.

javascript

const arr = ['x', 'y', 'z'];

// Wrong: trying to use entries() as an array
// console.log(arr.entries()[0]); // Error: entries() is not an array

// Correct: use for...of to iterate
for (const [i, val] of arr.entries()) {
  console.log(i, val);
}

Output

0 x
1 y
2 z

Quick Reference

Method	Description	Returns
array.entries()	Iterator of [index, value] pairs	Iterator object
array.keys()	Iterator of indexes (keys) only	Iterator object
array.values()	Iterator of values only	Iterator object

Key Takeaways

Use array.entries() to get both indexes and values when looping.

Use array.keys() to get only the indexes of array elements.

Both methods return iterators, so use for...of to loop through them.

Do not treat entries() or keys() as arrays directly.

These methods help write clear loops when you need positions or pairs from arrays.