javascript中isNaN和Number.isNaN之间的混淆 [英] Confusion between isNaN and Number.isNaN in javascript

问题描述

我对 NaN 的工作原理感到困惑.我已经执行了 isNaN(undefined) 它返回了 true .但如果我使用 Number.isNaN(undefined)，它会返回 false.所以我应该使用哪一个.还有为什么结果会有这么大的差异.

I have a confusion in how NaN works. I have executed isNaN(undefined) it returned true . But if I will use Number.isNaN(undefined) it is returning false. So which one i should use. Also why there is so discrepancy in the result.

推荐答案

引用一个 ponyfoo 关于 ES6 中数字的文章:

Number.isNaN 几乎与 ES5 全局 isNaN 方法相同.Number.isNaN 返回提供的值是否等于 NaN.这是一个与这不是一个数字吗?"非常不同的问题.

Number.isNaN is almost identical to ES5 global isNaN method. Number.isNaN returns whether the provided value equals NaN. This is a very different question from "is this not a number?".

所以 isNaN 只是检查传递的值是否不是数字或不能转换为数字.另一方面，Number.isNaN 仅检查值是否等于 NaN(尽管它使用与 === 不同的算法).

So isNaN just checks whether the passed value is not a number or cannot be converted into a Number. Number.isNaN on the other hand only checks if the value is equal to NaN (it uses a different algorithm than === though).

例如String 'ponyfoo' 不是数字，不能转换成数字，但不是NaN.

The String 'ponyfoo' for example is not a number and cannot be converted into a number, but it is not NaN.

例子:

Number.isNaN({});
// <- false, {} is not NaN
Number.isNaN('ponyfoo')
// <- false, 'ponyfoo' is not NaN
Number.isNaN(NaN)
// <- true, NaN is NaN
Number.isNaN('pony'/'foo')
// <- true, 'pony'/'foo' is NaN, NaN is NaN

isNaN({});
// <- true, {} is not a number
isNaN('ponyfoo')
// <- true, 'ponyfoo' is not a number
isNaN(NaN)
// <- true, NaN is not a number
isNaN('pony'/'foo')
// <- true, 'pony'/'foo' is NaN, NaN is not a number

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