Many of the great features of modern js (destructuring, fat arrows, splats) came directly from CoffeeScript. As much as I loved the comparative power of CoffeeScript (list comprehensions, everything is an expression), its time has past. There is very little active development and it has lost all momentum. It also never started addressing the biggest issue facing large JS projects, typing and static analysis. Refactoring a CS project is a fragile process that I won't miss.