I'd suspect they have several tools like this for code portability. It's relatively trivial to make a simple translator that compiles to Javascript; take Coffee

I'd suspect they have several tools like this for code portability. It's relatively trivial to make a simple translator that compiles to Javascript; take CoffeeScript for example. I'd be surprised if there weren't all sorts of tools like these floating around Redmond. The notion of a "runtime" sitting on top of Javascript? That doesn't even make sense. It would also be a waste of Anders's strengths. His strength is in taking something popular and making it modern and usable (e.g. Java -> C#). Coming from him, I'd expect more along the lines of a framework or language extension or ECMA contribution than a runtime or compiler.