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    Array.prototype.length

    Summary

    The length property represents an unsigned, 32-bit integer that specifies the number of elements in an array.

    Property attributes of Array.prototype.length
    Writable yes
    Enumerable no
    Configurable no

    Syntax

    arr.length

    Description

    The value of the length property is an integer with a positive sign and a value less than 2 to the 32nd 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. Thus, the length property says nothing about the number of defined values in the array. See also Relationship between length and numerical properties.

    Examples

    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. The value in each element 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]
    

    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;
    }
    

    Specifications

    Specification Status Comment
    ECMAScript 1st Edition. Standard Initial definition.
    ECMAScript 5.1 (ECMA-262)
    The definition of 'Array.length' in that specification.
    Standard  
    ECMAScript 6 (ECMA-262)
    The definition of 'Array.length' in that specification.
    Release Candidate  

    Browser compatibility

    Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes)
    Feature Android Chrome for Android Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile
    Basic support (Yes) (Yes) (Yes) (Yes) (Yes) (Yes)

    See also

    Document Tags and Contributors

    Last updated by: gtomitsuka,
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