That's kind of nasty. It's certainly fun to play with pathological language features, but it's not exactly a useful thing to test on when the answer is "don't do that". I'd enjoy a JavaScript quiz on some of the "wat?" features, but I wouldn't want to be evaluated on my ability to guess them.
Seriously! I think these sort of tricks are really fun (I read IOCCC and other stuff), but I only know this because of a famous codegolf answer that takes advantage of this trick [0].
I wouldn't expect anyone else to know it, and don't consider it something positive or negative as far as programming skill is concerned. It's kind of related to interest, but admittedly I waste a lot of time playing with stupid details like this in programming languages, so maybe it actually makes me less productive than the average person.
