JSEclipse is the the best and most popular Javascript plugin for the Eclipse environment. Its benefits are visible from the simplest tasks like editing small sections of code for your site to the more complex ones like working with the next big AJAX library or developing plugins for a product that embeds JavaScript like Dreamweaver or Photoshop.

JSEclipse :: Features
Code Completion

* Contextual code completion
* Support for major JavaScript libraries
* Code completion uses Rhino for better accuracy
* Use of JSDoc and inline parameter comments to detect parameter type
* Suggest parameters to be filled
* Project dependent code completion
* Reads all classes in current project
* Reads classes in currently opened files
* Scan current file for words
* Reads XML files for class definitions
* Add your own XML with class definitions

Productivity

* Content Outline
* Code templates
* Syntax Highlighting
* Syntax based code folding
* Open declaration
* Occurrence marker
* Integration with ATF
* Error reporting
* Reference library

Editing assistance

* Code editing helpers
* Edit in JSEclipse
* Word Wrap
* JavaDoc, multiline comments