javascript ide eclipse plugin web20 web-20 ajax
JSEclipse — (still) free and neat javascript editor, distributed as a plugin for Eclipse IDE.

Pros: Code outline is the best I’ve ever seen, syntax checking, support of popular javascript “Web 2.0″ libraries / frameworks like Dojo and Prototype.
Cons: Lacks source formatting and debugging (but its possible to debug using ATF technology)

Highlights in version 1.5:

• Revamped code completion for JavaScript function and classes.
• Common idioms used in JavaScript and major libraries like Dojo and Prototype.
• Outline panel shows class hierarchy.
• Syntax highlighting.Powerful editing assistance helpers.
• Support for JDK 1.4Code completion for JSDoc and inline parameter type definition.
• Open function declaration.Error reporting…

JSEclipse plugin homepage

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 ( If you install JSEclipse after you install ATF, you can still use JSEclipse as your JavaScript editor and get the best features of both worlds, smart code completion from JSEclipse and debugging from ATF.)
  ATF - AJAX Toolkit Framework, a technology that assists in constructing Eclipse framework support for AJAX Toolkits and provides enhanced DHTML/Javascript IDE features for AJAX developers.
• Error reporting
• Reference library

Editing assistance

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