array.unshift

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

var a = [1, 2, 3];
a.unshift(4, 5);

console.log(a); // [4, 5, 1, 2, 3]

Syntax

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

Parameters

elementN

The elements to add to the front of the array.

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.

Examples

var arr = [1, 2];

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

arr.unshift(-2, -1); // = 5
// arr is [-2, -1, 0, 1, 2]

arr.unshift([-3]);
// arr is [[-3], -2, -1, 0, 1, 2]

Specifications

Specification	Status	Comment
ECMAScript 3rd Edition (ECMA-262)	Standard	Initial definition. Implemented in JavaScript 1.2.
ECMAScript 5.1 (ECMA-262) The definition of 'Array.prototype.unshift' in that specification.	Standard
ECMAScript 2015 (6th Edition, ECMA-262) The definition of 'Array.prototype.unshift' in that specification.	Standard
ECMAScript 2017 Draft (ECMA-262) The definition of 'Array.prototype.unshift' in that specification.	Draft

Browser compatibility

See also

• Array.prototype.push()
• Array.prototype.pop()
• Array.prototype.shift()
• Array.prototype.concat()