That said: you go to war with the language you have, not the one you might want or wish to have.
ECMAScript is ECMAScript. Arguing that your transformation tool doesn't need to handle a feature specified in the language and supported by all known implementations is just ridiculous. Arguing that people making use of a feature that the language standard says they can (and that works) are "sloppy" is equally dumb. Even weirder are the people who jumped on the use of the && operator to effect an "if" as "abuse" -- this is an idiom pervasive in lots of areas and (again) well-supported by Javascript.
Not everyone is going to have the same aesthetics, everyone has a different idea about what features are "fun" and which are "sloppy". And decades of experience in the "code convention hell" world of enterprise programming has taught us nothing if not that this sort of pedantry helps no one. If you want to use Javascript, you have to take the whole language -- warts and all.