I politely submit that what you actually want is Python, Ruby, or Lua in the browser.
And by keeping to Javascript, only better and fixed, it would be easier to reuse and adapt huge parts of the browser ecosystem and toolchain.
Ruby maybe. Lua lacks proper unicode support. Python, I've used since 1998, but can't stand the lack of proper closures (and/or how the syntax makes them awkward) for web work.
And there's two more issues with all of them:
1) they are dog slow compared to modern JS JITs like V8 (and alternative implementations like PyPy are not as mature).
2) on the browsers, due to the sandbox and other issues, you can't use most of their libraries, that use native extensions and such, so you just get their syntax, not their batteries.
I'm thinking technologies like Skulpt or Pyjamas, that let you use Python in JS, are better. It's been a while since I investigated this situation, does anyone know of other players?