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.