I spent the last month on a project involving C++, C# and JS. The only thing that didn't went as smooth as I liked was the JS. Mainly due the fact that I cannot keep a whole API in my head. (The 8000 lines Anders is referring too.) As a matter of fact I was using a for me new API, three.js and it was just tedious. Opening files manually, looking for members all over the code etc... And then three.js is a nice structured library.
So I am off to download this as I've got work to do.