JavaScript: The Definitive Guide, 5th Edition

Name

Array.unshift( ): insert elements at the beginning of an array — ECMAScript v3

Synopsis

array.unshift(value, ...)

Arguments

value, ...

One or more values that are inserted at the start of array.

Returns

The new length of the array.

Description

unshift( ) inserts its arguments at the beginning of array, shifting the existing elements to higher indexes to make room. The first argument to shift( ) becomes the new element 0 of the array; the second argument, if any, becomes the new element 1; and so on. Note that unshift( ) does not create a new array; it modifies array directly.

Example

unshift( ) is often used in conjunction with shift( ). For example:

var a = [];             // a:[]
a.unshift(1);           // a:[1]          Returns: 1
a.unshift(22);          // a:[22,1]       Returns: 2
a.shift( );                // a:[1]          Returns: 22
a.unshift(33,[4,5]);    // a:[33,[4,5],1] Returns: 3

See Also

Array.shift( )