This has been covered over, and over, and over again. CoffeeScript has some explicit goals with respect to the generated JavaScript output, and that includes no

This has been covered over, and over, and over again. CoffeeScript has some explicit goals with respect to the generated JavaScript output, and that includes not mucking with your identifiers. In order to implement correct lexical scoping, you'd need to rewrite identifiers to avoid shadowing and collision. CoffeeScript's design is a very reasonable trade off given the inadequacies of JavaScript.