字符串作为数组的键 [英] Strings as keys of array

问题描述

当使用字符串作为数组的键时，console 显示没有这些声明值的数组，并且当键是字符串的时候通过这个值迭代时没有显示?，虽然我可以获得它们的价值.

When using strings as keys of an array, console is showing that the array without these declared values and while iterating by this values where keys are string aren't displayed? , although i can get value of them.

>> var arr = [ 0, 1, 2, 3 ];
   undefined

>> arr["something"] = "aught";
   "aught"

>> arr
   [0, 1, 2, 3]

>> arr["something"]
   "aught"

>> for( var i = arr.length; i--; console.log( arr[ i ] ) );
   3
   2
   1
   0

我知道数组是在 JavaScript 引擎中实现了某种枚举"接口的对象.

I understand that arrays are objects which has implemented some kind of 'enumerate' interface in JavaScript's engine.

最有趣的是解释器不会抛出警告或错误，所以我花了一些时间寻找数据可能丢失的地方.

Most interesting is that interpreter isn't throwing either warning or error, so I spent some time of searching for where data could be lost.

推荐答案

在 JavaScript 中有两种类型的数组:标准数组和关联数组

In javascript there are 2 type of arrays: standard arrays and associative arrays

• [ ] - 标准数组 - 仅基于 0 的整数索引
• { } - 关联数组 - javascript 对象，其中键可以是任何字符串

• [ ] - standard array - 0 based integer indexes only
• { } - associative array - javascript objects where keys can be any strings

所以当你定义:

var arr = [ 0, 1, 2, 3 ];

您正在定义一个标准数组，其中索引只能是整数.当你做 arr["something"] 因为 something (这是你用作索引的)不是一个整数时，你基本上是在为 arr 定义一个属性 对象(JavaScript 中的一切都是对象).但是您并没有向标准数组添加元素.

you are defining a standard array where indexes can only be integers. When you do arr["something"] since something (which is what you use as index) is not an integer you are basically defining a property to the arr object (everything is object in javascript). But you are not adding an element to the standard array.

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