Researching this a bit and reading over your comments it seems that you are using Eclipse with the Aptana extension. If you absolutely do not need to use the Eclipse environment you could now download the Aptana Studio 3 which is based on Eclipse. It looks just like eclipse but is Aptana. Now instead of entering this and looking for Aptana plugins you are going to go into Aptana and look for eclipse plugins. I've installed this myself and have installed several plugins that handle all sorts of things such as javascript code completion, source code formatting etc. If you go to this site http://www.aptana.com/ you can download the software there. To get all of the plugins, you can do use this site to guide you through some terrific source code completion utilities as well as others. http://jebaird.com/2012/11/02/useful-plugins-for-aptana-studio-3.html
His site isn't right on the money. I had to dig a little for some of them. I'll list the items he has below
To install do the following Help > Install new software > and clicking on the add button Name the site and then put in the url you're given once your items come up, make sure all the check boxes are selected and hit finish.
Hunspell for Eclipse http://hunspell4eclipse.googlecode.com/svn/trunk/com.lorands.hunspell4eclipse.updatesite/
JsHint http://github.eclipsesource.com/jshint-eclipse/updates/
Emmet
http://emmet.io/eclipse/updates/
Here is a javascript code formatter profile that is as close to the jQuery core style guide. You may or may not find it useful. You can find it here: https://github.com/jebaird/aptana-formatter-profiles
To import this style guide, download it and go to Window > Preferences > Aptana Stuido > Formatter. Click the import button
One of the most helpful things that I have found it is to search for eclipse plugins not aptana studio plugins. Since aptana is built on top of eclipse most of the plugins will work.