That NaN is considered a number in JS.

Half a day I spent figuring out what went wrong.

Not a number is a number!? 😱😱

That's JS. Cobbled together by a kid with a bottle of crazy glue.

NaN is More like the null value for numbers than an object of another type...

Yes, from a typesystem point of view, NaN is a number. It's a special numeric value to show that the value can't be represented. For the same reason, null's type is object, even though it represents that there is no object.

That's why JS has a function called isNaN(value)