为什么JavaScript说数字不是数字？ [英] Why JavaScript says that a number is not a number?

问题描述

我有一段JavaScript代码，预计会为变量设置一个整数值。

I have a piece of JavaScript code which is expected to set an integer value to a variable.

有些东西坏了，所以当我尝试<$ c时$ c> alert（A）; ，它返回 NaN 。 isNaN（A）; 返回true。但如果我 alert（typeof（A））; ，则说 number 。

Something is broken, so when I try to do alert(A);, it returns NaN. isNaN(A); returns true. But if I alert(typeof(A));, it says number.

那么变量怎么可以是一个数字而不是一个数字呢？也许我误解了NaN究竟是什么？

So how can a variable be a number and not a number at the same time? Maybe I misunderstood what NaN really is?

编辑：感谢答案，我明白了我错了，因为：

thanks to the answers, I see that I was wrong, because:

• NaN 的类型是数字，


• NaN 的意思是不是数字，这是不一样的不是类型数字，


• 0/0 是 NaN 的一个很好的例子：它仍然是一个数字，但JavaScript（没有其他人）可以说零的实际值除以零。另一方面， 1/0 返回 Infinity ，这不是 NaN 。

• The type of NaN is Number,
• NaN does mean "Not a number", which is not the same thing as "not of type Number",
• 0/0 is a good example of NaN: it is still a number, but JavaScript (and nobody else) can say what is the real value of zero divided by zero. 1/0 on the other hand returns Infinity, which is not NaN.

推荐答案

据我了解， NaN 是 Number 类的一个标记实例，它代表了它所代表的 - 无法充分表示的数字结果。所以 0/0 不是一个数字，因为它是 NaN ，但它是一个数字就其类型而言。

As I understand it, NaN is a sentinel instance of the Number class that represents, well, exactly what it stands for - numeric results that cannot be adequately represented. So 0/0 is not a number, in the sense that it's NaN, but it is a Number in terms of its type.

也许它应该被称为NaRN（不是可表示的数字） ）。

Perhaps it should have been called NaRN (Not a Representable Number).

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