That's a whole different matter, which can't make you shoot yourself in the foot without knowing it for any non-trivial code.

CoffeeScript's scoping forces you to always keep track of whatever is enclosing the current scope ALL THE WAY TO THE TOP. This is way too much when your function doesn't need to access outer variables (which should be the minority of the cases).

So, problem is, you either make all your functions have non-free variables (but Jashkenas seems to dislike functions shadowing outer variables too, which is just... overtly weird), or you keep track of all variables above the current scope.

The former is not too unreasonable, until you remember it makes no sense with closures :3

Yes, and it's very uncommon that you need to do that. I learned Scheme years ago before I learned Python (in 1993, I think). At first I was dismayed by Python's lack of non-local assignment. However, in years of Python programming I can count the times I needed the ability on one hand. I haven't yet found a need for 'nonlocal'.

Obviously it depends on programming style. In Coffeescript you don't have something akin to 'self' and so assigning to a non-local happens a lot.