Two easy to use Eclipse JS Editor plugin __js

Jseclipse
From the Workbench menu, select Help > Software Updates > Find and Install.
Select Search for new features to install.
Click Next to continue creating a new update site.
Create a new update site

New features and Plug-ins are hosted in a specific update site. Some of these sites have been preconfigured in the Eclipse installation, but you will need to add a new update site for Jseclipse:

Click the New Update Site on the right side of the window.

Enter the name Jseclipse (or any other name you remember) and the URL http://www.interaktonline.com/.
Http://download.macromedia.com/pub/labs/jseclipse/autoinstall Click OK to add the new site to the list.
Install Jseclipse

Spket
Spket profile: Is a great eclipse JavaScript plugin that supports the EXT library.

A development tool for RIA. Support for new products such as JavaScript, XUL/XBL, Laszlo, SVG and Yahoo! Widgets, which can run as a stand-alone desktop application or as a plugin in eclipse.

Install Spket under eclipse:

1, open eclipse,help > Software Updates-> Find and install...> Search for new features to Install->new remote SI Te ...
Name: "Spket", Url:http://www.agpad.com/update, and then automatically download Spket, now the latest version of 1.6.16, download a tantrum after the restart Eclipse completed the initial installation.

2, Window-> Preferences-> spket-> JavaScript Profiles New;
Enter "ExtJS" click OK;
Select "ExtJS" and click "Add Library" and select "ExtJS" in the dropdown bar;
Select "ExtJS" and click "Add file", and then locate the "EXT.JSB" file in your./ext-2.2/source directory and select Open.

3, select ExtJS, and then click on the right of default, set this to defaults, now in a JavaScript inside the input "EXT." See if a code hint will appear. If there is a proof of installation success ~ ~
You can also download the Eclipse plugin from the Web to install it, as with other Eclipse installation methods ~ ~