Officially released December 15th on Adobe Labs, JSEclipse is a new plugin for the Eclipse environment that helps developers code JavaScript faster and with no errors. With JSEclipse, you can complete a variety of tasks, from editing small sections of code to working with the next big AJAX library.
Check out JSEclipse on the Adobe Labs site here.

some comment
There is an error from JSEclispe
Reason:
com.interaktonline.jseclispe.ui.newwizard.JSClass
Hi Sang,
This is a known bug and it will be fixed in a future release. For more details, you can check out this forum thread:
http://www.adobe.com/cfusion/webforums/forum/messageview.cfm?forumid=72&catid=629&threadid=1224131&enterthread=y
Thanks,
Marius