javascript Array 索引 僅能用數值型態,物件的索引才能用字串型態的。

From: http://stackoverflow.com/questions/9526860/why-does-a-string-index-in-a-javascript-array-not-increase-the-length-size

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’ };

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