Currently I am writing more and more CoffeeScript. First I was not too impressed by it, due to the fact that it brings not much more to the table than syntactical sugar for JavaScript. I had a few discussions weather or not TypeScript is better, mainly because it already uses ECMAScript 6 functionality and extends on it. However, now after some more time coding CoffeeScript I really start to like it, because the main advantage is readability, and coming from Ruby, readability is what makes your code beautiful, understandable and maintainable (besides having a decent test suite).

A quick example that should express the readability:

# CoffeeScript
return unless target? && MutationObserver?

returns into

# JavaScript
if (!((target != null) && (typeof  MutationObserver !== "undefined" &&  MutationObserver !== null))) {