There are already a few approaches out there for compiling C# to JS, like my JSIL (http://jsil.org/ http://jsil.org/) and Script#'s unofficial successor, Saltar

There are already a few approaches out there for compiling C# to JS, like my JSIL (http://jsil.org/ http://jsil.org/) and Script#'s unofficial successor, Saltarelle (http://www.saltarelle-compiler.com/ http://www.saltarelle-compiler.com/). I believe there is a new Roslyn-based C#->JS compiler in the works as well. I'm not aware of anything that approaches WebSharper's level of integration, though. It's a really impressive piece of work.