IIRC the main appeal of CoffeeScript was syntactic sugar like lambda expressions etc that were missing in ECMAScript 5.
I think ECMAScript 6 made most of the appeal of CoffeeScript obsolete
When CoffeeScript came out, I vowed never to write plain Javascript again. I kept to that vow for a couple years, but eventually broke it when ECMA 6 came out. Really the only thing that put real technical justification behind CoffeeScript was the double arrow function, and maybe the neat class syntax. Beyond that CoffeeScript is just prettier. Even though I was in charge of choosing the technologies, you got to skate where the puck is going, and the puck was clearly not staying with CoffeeScript.
ECMA 6 copied all the good parts out of both CoffeeScript and jQuery, effectively obsoleting both. Modern JavaScript is almost unrecognisably different from what it used to be, and that's a very good thing.
