为什么是'null + 1 = 1'但却是'undefined + 1 = NaN'? [英] Why is `null + 1 = 1` but `undefined + 1 = NaN`?

问题描述

null + 1 = 1

undefined + 1 = NaN

我不明白这背后的逻辑是什么.都不应该都返回相同的结果吗?

I am not able to understand what is the logic behind this. Shouldn't both have returned same result?

推荐答案

基本上，因为这就是语言规范所说的内容-查看 ToNumber :

Basically, because that's what the language spec says - looking at ToNumber:

Type        Result
Null        +0
Undefined   NaN

NaN和任何东西都是NaN

从语言的角度来看，该可能有意义:null表示显式的空值，而undefined表示未知的值.以某种方式-零是数字空值"，因为它对加法是中性的.话虽如此-这是一个很大的延伸，我认为这通常是不好的设计.在真实的JavaScript代码中-您几乎永远不会在事物中添加null.

This might make some sense from the language perspective: null means an explicit empty value whereas undefined implies an unknown value. In some way - zero is the "number empty value" since it is neutral to addition. That said - that's quite a stretch and I think this is generally bad design. In real JavaScript code - you almost never add null to things.

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