sublime text editor is currently, by far, my favorite text editor/IDE. it’s power, though, comes from its extensibility. packages are where sublime text’s power is fully unleashed. there are tons of them out there and many, many blog posts about the best ones.
recently, i’ve discovered one that enables easy javascript auto-completion for sublime: tern for sublime. the install is not quite as straightforward as other plugins, but it does a pretty good job at providing auto-completion for javascript. based off tern, if you are a front end developer, i’d recommend checking it out.