Javascript [Electronic resources] : The Definitive Guide (4th Edition) نسخه متنی

Availability

JavaScript 1.1, JScript 2.0; ECMAScript v1

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 

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, the array is truncated and
elements at the end are lost. If you set length to
be larger than its previous value, the array becomes bigger and the
new elements added at the end of the array have the
undefined value.