I almost never work on client side scripting these days, but apparently InterAkt Online (of Dreamweaver fame, et al) has released a free plugin for Eclipse for JavaScript editing (via del.icio.us).

JSEclipse is a freeware Javascript plug-in for the Eclipse environment. Designed to help web developers edit JavaScript files with ease, it has built in support for:

* Code completion for JavaScript function and classes.
* Code completion for JavaDoc.
* Function and class names are displayed in the Outline panel for the currently open file.
* Open declaration
* Error reporting
* Warning reporting
* Code wrap