The copyWithin() method shallow copies part of an array to another location in the same array and returns it without modifying its length.
Array.prototype.copyWithin()
Try it
Syntax
copyWithin(target) copyWithin(target, start) copyWithin(target, start, end)
Parameters
-
target -
Zero-based index at which to copy the sequence to. If negative,
targetwill be counted from the end.If
targetis at or greater thanarr.length, nothing will be copied. Iftargetis positioned afterstart, the copied sequence will be trimmed to fitarr.length. -
startOptional -
Zero-based index at which to start copying elements from. If negative,
startwill be counted from the end.If
startis omitted,copyWithinwill copy from index0. -
endOptional -
Zero-based index at which to end copying elements from.
copyWithincopies up to but not includingend. If negative,endwill be counted from the end.If
endis omitted,copyWithinwill copy until the last index (default toarr.length).
Return value
The modified array.
Description
The copyWithin works like C and C++'s memmove, and is a high-performance method to shift the data of an Array. This especially applies to the TypedArray method of the same name. The sequence is copied and pasted as one operation; pasted sequence will have the copied values even when the copy and paste region overlap.
The copyWithin function is intentionally generic, it does not require that its this value be an Array object.
The copyWithin method is a mutable method. It does not alter the length of this, but it will change its content and create new properties, if necessary.
Examples
Using copyWithin
[1, 2, 3, 4, 5].copyWithin(-2) // [1, 2, 3, 1, 2] [1, 2, 3, 4, 5].copyWithin(0, 3) // [4, 5, 3, 4, 5] [1, 2, 3, 4, 5].copyWithin(0, 3, 4) // [4, 2, 3, 4, 5] [1, 2, 3, 4, 5].copyWithin(-2, -3, -1) // [1, 2, 3, 3, 4] [].copyWithin.call({length: 5, 3: 1}, 0, 3) // {0: 1, 3: 1, length: 5} // ES2015 Typed Arrays are subclasses of Array var i32a = new Int32Array([1, 2, 3, 4, 5]) i32a.copyWithin(0, 2) // Int32Array [3, 4, 5, 4, 5] // On platforms that are not yet ES2015 compliant: [].copyWithin.call(new Int32Array([1, 2, 3, 4, 5]), 0, 3, 4); // Int32Array [4, 2, 3, 4, 5]
Specifications
Browser compatibility
| Desktop | Mobile | Server | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | Deno | Node.js | |
copyWithin |
45
|
12
|
32
|
No
|
32
|
9
|
45
|
45
|
32
|
32
|
9
|
5.0
|
1.0
|
4.0.0
|
See also
© 2005–2022 MDN contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/copyWithin
