Why doesn't the method of the Number object run in this case?

Question

JavaScript

An object 's methodNumber isNaN must determine whether the value is NaNor not.

let a = 10;
console.log(a.isNaN()); //a.isNaN is not a function

Why is this method not found and just an error is thrown? Or I'm not looking at the methods there at all ...

Answer 1

The isNaN method, which is listed in the list of Number methods, is a method of the Number itself, and not an instance, so you need to call it:
Number.isNaN(a)

Answer 2

This is just a global function for checking for NaN, in ec6 it is also a static method of the Number.isNaN constructor.
It does not appear in the number prototype

Answer 3

In general, a function can be used and not as a method.
Like this:isNaN( value )