JavaScript: The Definitive Guide, Fourth Edition

Name

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

Availability

JavaScript 1.2; JScript 5.5; ECMAScript v3

Synopsis

                  array.unshift(value, ...)

Arguments

value, ...

One or more values that are to be 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( )