JavaScript (ES2026) reference · Array Methods

JavaScript Array fill() Method

Fill all or part of an array with a static value, changing it in place. Often used to create an array of defaults.

JavaScript (ES2026) Since ES2015

Syntax

array.fill(value, start, end)

Parameters

Parameter	Description
`value`	The value to fill with.
`start, end` optional	Only fill this range.

Return value

The modified array.

Examples

Fill an arrayTry it yourself

console.log(new Array(3).fill(0));
console.log([1, 2, 3, 4].fill(9, 1, 3));

Output

[ 0, 0, 0 ]
[ 1, 9, 9, 4 ]

Objects are sharedTry it yourself

const bad = new Array(2).fill([]);
bad[0].push("x");
console.log(bad); // the same array twice!
const good = Array.from({ length: 2 }, () => []);
good[0].push("x");
console.log(good);