[Chapter 21] Reference: Array.length
Author: David Flanagan
Date: Fri Aug 29 11:13:56 1997

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| Chapter 21 JavaScript Reference |

# Array.length Property

## Name

Array.length Property---the size of an array

## Availability

Navigator 3.0, Internet Explorer 3.0

## Synopsis

    array.length

## Description

The `length` property of an array is always one larger than the highest element defined in the array. For traditional "dense" arrays that have contiguous elements and begin with element 0, the `length` property specifies the number of elements in the array.

The `length` property of an array is initialized when the array is created with the `Array()` constructor method. Adding new elements to an array updates the `length`, if necessary:

    a = new Array();    a.length initialized to 0
    b = new Array(10);  b.length initialized to 10
    c = new Array("one", "two", "three");   c.length initialized to 3
    c[3] = "four";  c.length updated to 4
    c[10] = "blastoff"; c.length becomes 11

Note that all JavaScript objects can be used as arrays, but only those created with the `Array()` constructor have an automatically created and updated `length` property.

You can set the value of the `length` property to change the size of an array. If you set `length` to be smaller than its previous value, then the array will be truncated, and elements at the end will be lost. If you set `length` to be larger than its previous value, then then the array will become bigger, and the new elements added at the end of the array will have the special JavaScript undefined value.

## Usage

The `Array()` constructor and `length` field were added to JavaScript in Navigator 3.0. Some Navigator 2.0 programs attempt to simulate a `length` field by setting it in the array constructor methods they write. Note, however, that the `length` field is not automatically updated as elements are added to the array. Nor can it grow or shrink the array when its value is set.

## See Also

"Array", Chapter 8, Arrays

Array.join() |  | Array.reverse()