The key thing is that javascript is built into emacs, which is a good argument for javascript to be built into any serious programmer's editor (since (a) chance

The key thing is that javascript is built into emacs, which is a good argument for javascript to be built into any serious programmer's editor (since (a) chances are good the programmer knows javascript, (b) you can get a good javascript engine for cheap, (c) many programmers will actually be using your editor to write javascript as a bonus). I was playing around with another interesting editor (Chocolat) which actually uses a Javascript engine to identify symbols in Javascript source files; but it does this far worse that can be done easily with regex (and in fact makes terrible errors doing so). Indeed, better results than that shown in the article are achieved by fancy new editors (like Espresso) and crufty old editors (like BBEdit) using regex and brute force. Fundamentally you've got an anonymous function or a function with a common name, and you want some outer context to further identify it -- regex can do that.