Since he wants that feature to work for Javascript, cscope is irrelevant anyway.
Well if he wanted code navigation for JavaScript he could have used tern. It also integrates nicely with company for auto-completion.
Or tide, which uses the typescript tsserver-backend for all its code-analysis.
Gives you navigation, refactoring, completion, eldoc etc. Basicslly JS on steroids.
cscope may be irrelevant, but ctags/etags has support for JS (and other languages that would be relevant for web developers, like HTML, PHP, Python, Ruby, SQL, ...).