Hmm is there good source of examples of refactoring Tern.js supports?

You are correct that need of those features leads to wanting to refactor your code in a way that you need to rely on them less. Still the case when dealing with legacy code. On work some of the stuff was written 4 years ago. In JavaScript world that’s like different world… This where typescript also helps but may be Tern can too. I wonder how it compares to what WebStorm does, if similar then TypeScript still is way ahead on that.