Rich clients were hot. They still are but the attention is drifting from anything rich client to just javascripting. The JS frameworks are literally popping up overywhere.

Before getting into these frameworks like jQuery, backbone, angularJS, … or the even aging prototype you should really look into the basics of javascripting. A lot of Java developer are forced back in the Javascripting world. These are some articles to get you going again. 

https://developer.mozilla.org/en-US/docs/JavaScript/Introduction_to_Object-Oriented_JavaScript

http://arstechnica.com/information-technology/2007/08/javascript-for-all-ages/