Difference between isNaN and Number.isNaN

Almost everyone knows what `isNaN` is and how to use it. It means “ is that thing that looks like a number, really a number or not?” It returns true if given is “Not a Number”. I assume you got the point. Ok, now here is the deal; what is the difference between isNaN and Number.isNaN?

Let’s start with isNaN. This is a global function you can call from everywhere. Let’s see it in action:

It is that simple but there are some misdirections. Here are the examples:

As you can see according to isNaN implementation treats string value as number and returns the result based on this.. Check `isNaN(‘blabla’)`

In my case I have a method which accepts two parameters as number type and do some animation on scaling of target object. Somehow after doing little refactoring I got weird behaviour. Yes, I should have written unit tests, shame on me. Anyway, for some cases the method receives undefined as parameters. So I need to check them.

I wrote this:

My carelessness leads me to wrong logic. Because Number.isNaN(undefined) will return me false. (old isNaN(undefined) returns true) So I changed like this:

So it seems to be working. But I wanted to care every possible failure. Maybe I might receive null instead of undefined. If I receive null my logic will fail. Why?

I think you see the thing. So I updated the code like this:

My goal was checking two values against to be undefined or null. And my journey ends up writing that article and updating my knowledge. The implementation is not fancy I know but the journey was educative.

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