Passing Context in CoffeeScript
The CoffeeScript looks fine to me. You'll still need the context var just as in plain JS, because you're not dealing with this. If you were, you could maybe use the fat arrow to preserve the this context, but even so it'd require some refactoring, and end up very different from the original JS.

CoffeeScript's fat arrow is basically meant to be used where you'd otherwise do the var that = this; trick in JavaScript. But since you're not doing such things in your JavaScript, there's no need or opportunity for it in the CoffeeScript either.