为什么NaN === NaN是假的？ [英] Why is NaN === NaN false?

问题描述

为什么 NaN === NaN 在Javascript中返回 false ？

Why does NaN === NaN return false in Javascript?

> undefined === undefined
true
> NaN === NaN
false
> a = NaN
NaN
> a === a
false

在文档页面我看到了：

针对NaN的测试

平等运营商（ == 和 == = ）不能用于测试 NaN 的值。请改用 isNaN 。

Testing against NaN

Equality operator (== and ===) cannot be used to test a value against NaN. Use isNaN instead.

是否有任何参考可以回答问题？这将是受欢迎的。

Is there any reference that answers to the question? It would be welcome.

推荐答案

严格答案：因为JS规范这样说：

• 如果Type（x）是Number，那么
  
  
  
  
  • 如果x是NaN，则返回false。
  
  
  • 如果y是NaN，则返回false。
  
  

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有用的答案：浮点数的IEEE 754规范（所有语言都用于浮点数）表明NaN永远不会等于。

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Useful answer: The IEEE 754 spec for floating-point numbers (which is used by all languages for floating-point) says that NaNs are never equal.

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