I've been playing with LiveScript a bit lately and have really been enjoying it! If you haven't heard of LiveScript, it's a "...fork of Coco, which is in turn derived from CoffeeScript..." (LiveScript Overview Page). It provides more features than Coco and CoffeeScript including several that assist in writing code in a more functional style.
Here's a quick example of a test written in LiveScript for Mocha and ExpectThat:
This shows off a couple of the features that help you write in a functional style with LiveScript. The first is the use of pattern matching within the isWeekend function. The second is the use of the pipe-forward operator when calling the isWeekend function.
F# has these same concepts and many more, which makes LiveScript + F# a compelling combination!
There are a number of additional LiveScript features that assist in using a functional style. For more examples of LiveScript with Mocha and ExpectThat visit https://github.com/dmohl/expectThat/tree/master/example/mocha-LiveScript. To learn more about LiveScript, see a number of examples, and/or get setup for use, visit the LiveScript site at http://gkz.github.com/LiveScript/.