Yeah, JavaScript has a pile of terrible type coercions, implicit conversions and misuse/reuse of operators. It was a bad 90s/00s trend to do this kind of thing; re-use + for string append, or coerce things into strings for convenience. Python and Ruby have their own gotchas, though not as bad.

You might enjoy this classic comedy routine: https://www.destroyallsoftware.com/talks/wat