为什么javascript数组中的字符串索引不会增加长度大小？ [英] Why does a string index in a javascript array not increase the length size?

问题描述

在下面的例子中，array2.length只有十，在我看来，它应该是13.为什么字符串键入索引不会增加数组的长度？我可以存储并仍可访问它，VS调试器显示这些数组正确存储。那么为什么长度没有增加？

In the example below, the array2.length is only ten, when 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 = "";

推荐答案

Javascript数组不能包含字符串索引。 Javascript 数组仅以数字方式编入索引。设置字符串索引时，您将设置对象的属性。这些是等价的：

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';

这些属性不属于数组的数据存储。

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

如果你想要关联数组，你需要使用一个对象：

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

var obj = {};
obj['a'] = 'foo';

也许最简单的可视化使用文字符号而不是 new Array ：

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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