浮点数组索引如何解释? [英] How are floating point array indices interpreted?

问题描述

我找不到关于此的任何信息，但假设我有

I can't find any information on this, but suppose I have

var arr = [1, 2, 3];
var x = arr[1.5];

我假设Javascript将floor索引并返回索引1处的项目，但似乎至少在Chrome中，它仅返回undefined.

I assumed that Javascript would floor the index and returns the item at index 1, but it seems at least in Chrome it just returns undefined.

这是正确的吗?我找不到任何可以证实这一点的标准或文档.如果这样的话，那真的很不方便，因为我认为舍入行为允许您将范围为[0，n)的任何浮点数传递给数组索引，但是如果执行浮点数学运算，看来您会默默地破坏数组.没有四舍五入.

Is this correct? I can't find any standard or documentation that confirms this. It's actually really inconvenient if so because I assumed the round-down behavior allows you to pass any float in the range [0, n) to an array index, but it seems you'll silently break your arrays if you do floating point math which isn't rounded.

如果有人维护javascript陷阱列表，请添加此列表.现在，我必须回顾1万行javascript代码，以查看我所做的这种假设在哪里悄悄地引起了错误！

推荐答案

根据 MDN:数组，数组项实际上是属性，而属性由字符串标识.

According to MDN: Array, array items are actually properties, and properties are identified by strings.

因此，访问arr[1.5]与访问arr['1.5']相同，而Firefox实际上就是这样做的.

Accessing arr[1.5] is therefore the same as accessing arr['1.5'], and Firefox does actually do it that way.

此代码:

var x = [0,1,2,3,4,5];

x[1.5] = 42;

alert(x);
alert(x['1.5']);
alert(x['1.50']);

输出:

 0, 1, 2, 3, 4, 5
 42
 undefined

因此，使用浮点值访问的项是由数字的字符串表示形式标识的属性.请注意，使用'1.50'访问项目与使用'1.5'访问项目不同，因此索引不会转换为数字.

So, the item accessed using a floating point value is a property identified by the string representation of the number. Note that accessing an item using '1.50' is not the same as accessing an item using '1.5', so the index is not converted to a number.

我也在Internet Explorer和Chrome中对此进行了测试，它们的作用都与Firefox相同.

I tested this in Internet Explorer and Chrome also, and they both do the same as Firefox.

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