Web/JavaScript/Reference/Global objects/Array/unshift

The unshift() method adds one or more elements to the beginning of an array and returns the new length of the array.

Syntax

arr.unshift(element1[, ...[, elementN]])

Parameters

elementN: The elements to add to the front of the arr.

Return value

The new length property of the object upon which the method was called.

Description

The unshift method inserts the given values to the beginning of an array-like object.

unshift is intentionally generic. This method can be called or applied to objects resembling arrays. Objects which do not contain a length property—reflecting the last in a series of consecutive, zero-based numerical properties—may not behave in any meaningful manner.

Please note that, if multiple elements are passed as parameters, they're inserted in chunk at the beginning of the object, in the exact same order they were passed as parameters. Hence, calling unshift with n arguments once, or calling it n times with 1 argument (with a loop, for example), don't yield the same results.

See example:

let arr = [4, 5, 6]

arr.unshift(1, 2, 3)
console.log(arr);
// [1, 2, 3, 4, 5, 6]

arr = [4, 5, 6] // resetting the array

arr.unshift(1)
arr.unshift(2)
arr.unshift(3)

console.log(arr)
// [3, 2, 1, 4, 5, 6]

Examples

Using unshift

let arr = [1, 2]

arr.unshift(0)               // result of the call is 3, which is the new array length
// arr is [0, 1, 2]

arr.unshift(-2, -1)          // the new array length is 5
// arr is [-2, -1, 0, 1, 2]

arr.unshift([-4, -3])        // the new array length is 6
// arr is [[-4, -3], -2, -1, 0, 1, 2]

arr.unshift([-7, -6], [-5])  // the new array length is 8
// arr is [ [-7, -6], [-5], [-4, -3], -2, -1, 0, 1, 2 ]

Specifications

Specification

ECMAScript (ECMA-262)The definition of 'Array.prototype.unshift' in that specification.

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile						Server
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet	Node.js
`unshift`	Chrome Full support 1	Edge Full support 12	Firefox Full support 1	IE Full support 5.5	Opera Full support 4	Safari Full support 1	WebView Android Full support 1	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 10.1	Safari iOS Full support 1	Samsung Internet Android Full support 1.0	nodejs Full support 0.1.100

Legend

Full support: Full support