typeof NaN in JS is "number"

and.. yeah thats it, no other jokes are necessary here I guess

undefined is a string. bigger joke for me.

well its funny, but its clearly logical. At very begining you need to understand primitives in js. Then read about numbers standard in js (and many others languages share the same standard). That will explain purely why typeof NaN is number and why NaN === NaN is false. Basics, very logical basics. Your lack of knowledge is not an issue of language.

@mort JavaScript doesn't make any sense!

Until you understand it. 😉

@mort any book to learn that?

@plateadoDev try googling "you don't know js"