Compilation of JavaScript is a terrible idea. I have worked with loads of different compile to JS languages. The compile step is a huge pain. The language has to be much much much better than JS for it to be worthwhile. I think that even JSX or TypeScript don't cut it... Close but still not worth the hassle! I used CoffeeScript for 6 months, it was a very lucrative contract but I had to quit in part because I really didn't like CoffeeScript.
What I love in a language is simplicity and unfortunately, you cannot make something simpler by adding a layer of complexity on top of it. It might look simpler at first glance, but it isn't once you start debugging, messing with source maps and buggy source code watchers.
If there was a native CoffeeScript interpreter inside browsers, then I might consider using it... Otherwise, no.