Coincidently, I'm currently creating a similar project: https://github.com/chrisdunelm/Cil2Js

This is absolutely not yet ready for real use, but can convert a sub-set of CIL to JavaScript and is fully open source :)

Update:

il2js and Cil2Js work significantly differently. il2js interprets the .NET IL in a JavaScript virtual machine, whereas Cil2Js directly converts the .NET IL into JavaScript.

Having now looked at this il2js project in more detail, it appears to have some subtle (and some not-so-subtle) differences between running on .NET and running in JS. For example, integer division will return a double in JS; Stack<T>.Last() returns wrong end of stack on JS; no/little support for non-primitive value types; etc... Hopefully these will be sorted out soon, as it's these sorts of inconsistencies that can lead to extreme frustration.

I am unconvinced that a JS VM is a good technique, as I suspect it will be an order of magnitude slower that the same IL converted to JS (although I have no test data to prove this).

However, these aside, it's an impressive project.