I was playing with similar idea. To provide browser-based playground for bitcoin scripts.

Technically my approach was different. I used emscripten to compile bitcoin sources into javascript and exposed simple wrapper of its functionality.

Interesting excercise, never finished :(

https://dl.dropboxusercontent.com/u/559047/bitcoin-emscripte...

https://dl.dropboxusercontent.com/u/559047/tx-verification.p...