Question

175

Why does a string index in an array not increase the 'length'?

rated 0 times [ 176] [ 1] / answers: 1 / hits: 103139 / 13 Years ago, fri, march 2, 2012, 12:00:00

In the example below, the array2.length is only 10, while in my mind, it should be 13.

Why does the string keyed indexes not increase the length of the array?

I can store things and still access it, and the VS debugger shows that those arrays are being stored properly. So why is the length not increased?

var array2 = new Array();

array2[a] = new Array();

array2[b] = new Array();

array2[c] = new Array();

for (var i = 0; i < 10; ++i)

    array2[i] = new Array();



var nothing = ;

for (var i = 0; i < array2.length; ++i)

    nothing = ;

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answered 13 Years ago stacied · Accepted Answer

Javascript arrays cannot have string indexes. A Javascript Array is exclusively numerically indexed. When you set a string index, you're setting a property of the object. These are equivalent:

array.a = 'foo';

array['a'] = 'foo';

Those properties are not part of the data storage of the array.

If you want associative arrays, you need to use an object:

var obj = {};

obj['a'] = 'foo';

Maybe the simplest visualization is using the literal notation instead of new Array:

// numerically indexed Array

var array = ['foo', 'bar', 'baz'];



// associative Object

var dict = { foo : 42, bar : 'baz' };