JavaScript (ES2026) reference · Array Methods

JavaScript Array copyWithin() Method

Copy a slice of the array to another position in the same array, overwriting what's there. Changes the array in place.

JavaScript (ES2026) Since ES2015

Syntax

array.copyWithin(target, start, end)

Parameter	Description
`target`	Index to copy to.
`start` optional	Index to start copying from. Default: `0`
`end` optional	Index to stop copying before. Default: `array.length`

The same, modified array.

Copy the last two to the frontTry it yourself

const nums = [1, 2, 3, 4, 5];
nums.copyWithin(0, 3);
console.log(nums);

Output

[ 4, 5, 3, 4, 5 ]

Copy a rangeTry it yourself

console.log([1, 2, 3, 4, 5].copyWithin(1, 0, 2));

Output

[ 1, 1, 2, 4, 5 ]

Version	Change
JavaScript ES2015	Added

array.fill() · Fill all or part of an array with a static value, changing it in place. Often used to create an array of defaults.
array.splice() · Remove, replace or insert elements at a position, changing the array in place. Returns the removed elements.
JavaScript Arrays · tutorial
JavaScript Array Methods · tutorial