You should check out ext.js if you haven't, they have most of the components Flex has and then some.
As far as performance, I don't know how they compare, but that wouldn't be the point to writing such a port. The point is that many applications will not use Flex because targetting AVM limits their ability to be on tablets and mobile devices as a web application. Compiling to JavaScript would solve that while providing a more robust application framework with type safety to develop in. -omar
