Core JavaScript 1.5 Reference:Global Objects:Array:length

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Contents 1 Summary 2 Description 3 Examples 3.1 Example: Iterating over an array 3.2 Example: Shortening an array

[edit] Summary

An unsigned, 32-bit integer that specifies the number of elements in an array.

Property of Array
Implemented in:	JavaScript 1.1, NES 2.0 JavaScript 1.3: length is an unsigned, 32-bit integer with a value less than 232.
ECMA Version:	ECMA-262

[edit] Description

The value of the length property is an integer with a positive sign and a value less than 2 to the 32 power (2³²).

You can set the length property to truncate an array at any time. When you extend an array by changing its length property, the number of actual elements does not increase; for example, if you set length to 3 when it is currently 2, the array still contains only 2 elements.

[edit] Examples

[edit] Example: Iterating over an array

In the following example the array numbers is iterated through by looking at the length property to see how many elements it has. Each value is then doubled.

var numbers = [1,2,3,4,5];
for (var i = 0; i < numbers.length; i++) {
  numbers[i] *= 2;
}
// numbers is now [2,4,6,8,10];

[edit] Example: Shortening an array

The following example shortens the array statesUS to a length of 50 if the current length is greater than 50.

if (statesUS.length > 50) {
   statesUS.length=50
}