What is the difference between isNaN and Number.isNaN in js

Difference: Number.isNaN does not have type conversion behavior, and isNaN will try to convert the parameter into Number type. isNaN only determines whether the incoming parameter can be converted into a number, and does not strictly determine whether it is equal to NaN; while Number.isNaN determines whether the incoming parameter is strictly equal to NaN.

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## isNaN

When we pass a parameter to isNaN, its original intention is to try to convert the parameter into Number type through the Number() method. If it succeeds, it returns false. If it fails, it returns true.

So isNaN only determines whether the incoming parameter can be converted into a number, and does not strictly determine whether it is equal to NaN.

Example:

Number('测试')

Because "test" was not successfully converted into Number type, the following code outputs true

console.log(isNaN('测试')) //true

Number. isNaN

# Determines whether the incoming parameter is strictly equal to NaN (that is, ===).

So under what circumstances is Number.isNaN generally used?

When two variables are operated on, we can use Number.isNaN to determine whether its value is NaN

console.log(Number.isNaN(1/'测试')); //输出true

The difference between the two

The biggest difference between Number.isNaN and isNaN is that Number.isNaN does not have type conversion behavior.

console.log(isNaN('测试')) //true
console.log(Number.isNaN('测试')) //false

In the above code, the string "test" is passed in, but why are the results different? The reason is:

isNaN tries to convert the string "test" into the Number type through the Number method, but the conversion fails because the result of Number('test') is NaN, so it finally returns true.

The Number.isNaN method only strictly determines whether the incoming parameters are all equal to NaN ('test' === NaN). Of course, the strings are not all equal to NaN, so it outputs false.

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