First, Update spket from site: http://www.spket.com/update using eclipse 3.5's install manager, note that spket's not a free software:)
Second,Config spket as following, make sure ext version is: 3.x.Also make sure you Make the Ext3.2.1 to be the default.
Third,Create a new Js file as:
Open this file using spket editor as:
Open this js file, the content assist button: "alt+/" can solve problems for you: