javascript - javascript 中 isNaN 和 Number.isNaN 的混淆

Question

我对 NaN 的工作原理感到困惑。我执行了 isNaN(undefined) 它返回了 true 。但是，如果我将使用 Number.isNaN(undefined)，它将返回 false。那么我应该使用哪一个。还有为什么结果会有这么大的差异。

Answer 1

引用自ponyfoo article on numbers in ES6 :

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 只检查值是否等于 NaN(尽管它使用与 === 不同的算法)。

例如字符串'ponyfoo'不是数字，不能转换成数字，但它不是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