Javascript analysis tools? IDE?

Does anybody have any favorite Javascript analysis tools, scripts, or an IDE that they find really helpful? Yeah, I know, "emacs and Venkman"--but is there something better to tackle the complexity when the source gets above 10,000 lines (!?!).

I have to deal with a mountain of inherited, undocumented javascript. Any hints? Any Javascript best practices/documentation approaches that have worked for you?