Small comment: I see this as a dart contender, from what I hear, there is a Visual Studio debugger coming, meaning we will be able to debug c#, but have it walk through javascript on page. Sounds amazing to me, thought I should share.
Follow the link in the readme to more detailed documentation. The amazing thing here, is that the produced javascript is small enough to warrant using it for real projects.The compiler is not yet open source, they said that if there is more interest, they will open it later.