copyWithin

The copyWithin() function copies a portion of the array to another location while remaining pure (the original array is cloned).

Interactive example

Syntax

Classic signature

function copyWithin<
	GenericElement extends unknown
>(
	input: readonly GenericElement[],
	target: number,
	start: number,
	end?: number
): GenericElement[]

Curried signature

function copyWithin<
	GenericElement extends unknown
>(
	target: number,
	start: number,
	end?: number
): (input: readonly GenericElement[]) => GenericElement[]

Parameters

• input: Source array.
• target: Index from which the copied portion will be written.
• start: Start of the portion to copy (inclusive).
• end: End of the portion (exclusive). Defaults to the end of the array.

Return value

A new array where the portion [start, end) has been copied starting at target. Unaffected sections remain identical.

See also

• fill - Overwrites a range with a fixed value
• set - Changes a single position

Sources

• MDN Web Docs - Array.prototype.copyWithin()