The built-in js-mode in Emacs does not provide many features for working with js framework beside js editing and syntax highlighting. The tips in this post will help you transform your Emacs into a powerful Javascript IDE.

Tern is a stand-alone code-analysis engine for JavaScript. It is intended to be used with a code editor plugin to enhance the editor's support for intelligent JavaScript editing. Features provided are:

Autocompletion on variables and properties
Function argument hints
Querying the type of an expression
Finding the definition of something
Automatic refactoring 

Tern is open-source (MIT license), written in JavaScript, and capable of running both on node.js and in the browser.