My suggestion would be to learn Sencha ExtJs [1]. It has a proper MVC framework and is very mature compared to the others mentioned here.
It's not something that can be learnt over the weekend and takes time to master.
Just like Rails, it seems to be able to a lot of things by magic and needs some dedicated effort to understand. This article from their blog [2] and this video [3] gives a very good comparison of what Sencha ExtJs covers with respect to other Javascript frameworks.