Gamma is a HTML5 framework I made for creating games. As an experiment I've used it to port two games: This Precious Land and HerpFortress. Also, there's a half-finished .obj viewer lying around somewhere, that's using it too. I have provided some thoughts on my HTML5 development experiences.
I used Google's Closure Compiler to provide a more sane development environment. It does this by providing namespaces and type annotations. However, namespaces cannot be imported, so you're left writting things out the long way. In the end, I guess the big-win is being able to statically compile to a single source file.
I do enjoy benefits of using a scripting language; specifically the read-eval-print loop. It means you can manipulate code at run-time, instead of waiting for compiles. This shortens the programmer feed-back loop, which can lead to new code discoveries. Also, it means iteration is quick.