A quickie here. I had written some code in javascript to simplify testing of a fairly dense, multi-dimensional feature area.  I could define the dimensions I wanted to test declaratively in a more or less JSON fashion and then bang them together via some enumerable-like extensions that I had written.  Viola, full test matrix implemented.

Unfortunately, I learned that I would be unable to take a dependency on the scripting host at run-time.  Too bad I had already invested the time in the solution, and I would now have to code the matrix myself.  But wait, this is a dynamic language I'm dealing with!  So, in a short time, I did some object substitution, and now my javascript is a precompiler that emits C# and other support files that I then compile to do the same thing.

Nikhil has a more general tool that goes the other way.  It compiles C# into javascript for use in AJAX apps.  While this is a handy way for people unfamiliar with the power of dynamic languages to jump into the AJAX world, I'm wondering if it's really a good idea in the long term.  On the one hand, reducing the number of language dependencies in a project is good for maintainability, but choosing the less-flexible one seems like the wrong choice.  Of course javascript has no formal set of class libraries, so that's a limitation.  Hmmm.  I'll have to think about this some more.