The resolution of the screen cast was not high enough for me to read the text he was typing.
As for usefulness, "my favorite language -> Javascript" compilers are cute, but I am skeptical of adding another leaky abstraction layer. Javascript is a pretty feature-ful, modern language with closures, first class function, collection literals, and some pretty good APIs. Not sure if bridging to other languages will give much of a productivity boost over just learning Javascript well, and you will probably need to learn Javascript well, anyways, whenever the translation from your favorite language to Javascript inevitably leaks.
Yeah, I sort of feel like this is safest at a relatively simple scale where the efficiency gains also stand to be the smallest. Although I heart Ruby, personally, I'd be more interested to see someone nail the deep javascript stack with quality. Something like Rhino on Rails on the server, javascript/AJAX client/server, CouchDB w/ javascript views for the DB and AIR for javascript/AJAX desktop apps and widgets. Seems like with JSON around, that could be elegant and efficient at larger scales, rather than generating code from one language to another for some pieces.
My personal pet peeve is that a language for the browser was standardized, instead of a simple generic bytecode format. But then I have a whole lots of pet peeves about the browser as a development platform.
I feel like I have to work harder with Javascript than with other languages to understand what is going on. One example is the definition of classes. I have to execute each line of code in my head in order to see the big picture. Classes seem to be more succinctly expressed in other languages.
I watched the demo over the weekend and was pretty impressed with what they're doing. Being able to write client-side and server-side code without switching contexts should yield a nice productivity boost.
As for usefulness, "my favorite language -> Javascript" compilers are cute, but I am skeptical of adding another leaky abstraction layer. Javascript is a pretty feature-ful, modern language with closures, first class function, collection literals, and some pretty good APIs. Not sure if bridging to other languages will give much of a productivity boost over just learning Javascript well, and you will probably need to learn Javascript well, anyways, whenever the translation from your favorite language to Javascript inevitably leaks.