>He is asking me about why a JS compiler is removing his comments

Huh ? language parsers remove comments because they're comments, that's literally by definition. Are you (or your past interviewer) using "comments" in a different sense ?

(Also, not trying to be a pedant on you I swear, but technically JS is traditionally interpreted. Most mature runtimes have compilers but it's not part of the API. It's just a juvenile pet peeve of mine when language implementations are generically referred to as compilers.)

>he actually said as I was leaving "make sure you understand databases for your next interview" with a massive shit-eating grin

I sincerely hope from my heart of hearts that company or department is in it's well deserved position in the depths of the toilet now, or at any rate that specific person.