JavaScript 数组中的负索引是否会影响数组长度?

问题描述：

在javascript中我定义了一个这样的数组

In javascript I define an array like this

var arr = [1,2,3];

我也可以

arr[-1] = 4;

现在如果我这样做

arr = undefined;

我还丢失了对 arr[-1] 处的值的引用.

I also lose the reference to the value at arr[-1].

所以对我来说，从逻辑上讲，arr[-1] 也是 arr 的一部分.

SO for me logically it seems like arr[-1] is also a part of arr.

但是当我执行以下操作时(没有将 arr 设置为 undefined)

But when I do following (without setting arr to undefined)

arr.length;

它返回3而不是4；

所以我的观点是如果数组可以用于负索引，这些负索引也应该是它们长度的一部分**.我不知道是我错了，还是我遗漏了一些关于数组的概念.

So my point is if the arrays can be used with negative indexes, these negative indexes should also be a part of their length**. I don't know may be I am wrong or I may be missing some concept about arrays.

答

所以对我来说，从逻辑上讲，arr[-1] 也是 arr 的一部分.

SO for me logically it seems like arr[-1] is also a part of arr.

是的，但不是你想的那样.

Yes it is, but not in the way you think it is.

您可以为数组分配任意属性(就像 JavaScript 中的任何其他对象一样)，这就是您在 -1 处索引"数组并分配值时所做的.由于这不是数组的成员而只是一个任意属性，因此您不应期望 length 考虑该属性.

You can assign arbitrary properties to an array (just like any other Object in JavaScript), which is what you're doing when you "index" the array at -1 and assign a value. Since this is not a member of the array and just an arbitrary property, you should not expect length to consider that property.

换句话说，下面的代码做了同样的事情:

In other words, the following code does the same thing:

var arr = [1, 2, 3];

arr.cookies = 4;

alert(arr.length) // 3;

JavaScript 数组中的负索引是否会影响数组长度?

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