Google's build the Android Development Environment for Eclipse, the Google Plugin for Eclipse (AppEngine and GWT integration) and Dart already released an Eclip

Google's build the Android Development Environment for Eclipse, the Google Plugin for Eclipse (AppEngine and GWT integration) and Dart already released an Eclipse environment, and a compiler. So the history seems to be that Google supports tools. Google is taking part is JS cleanup efforts, but it's a large company with 20,000+ employees, so it has the reasons to pursue many different paths: Closure, GWT, Dart, Go, etc. As for runtime improvement, if the team who has built the one of the best/fastest JS VMs (V8 team) says the language semantics allow them to do better, I think we should listen. The early binding alone allows for substantial improvement. If all classes are early bound, then you can significantly optimize dead code, you can know object layouts immediately on load, you can detect effectively non-virtual methods immediately, and so on. You can pretty much snapshot important information that you normally have to discover each and every time you load the application.