bug#47488: Treatment of # in js.el

[Dmitry Gutov]

On 30.03.2021 00:28, Reuben Thomas via Bug reports for GNU Emacs, the 
Swiss army knife of text editors wrote:
> Is this just because the code was originally based on cc-mode or 
> something, and the references to hash were never removed? Or was cpp 
> used with early JavaScript?? I see references such as js--opt-cpp-start 
> which says "Regexp matching the prefix of a cpp directive", and a match 
> for "#define" in js--update-quick-match-re.

IIRC this was related to the use of the C preprocessor in some JS 
codebases (Mozilla?). Not sure if that practice stopped.