Chapter 1. CoffeeScript Syntax

Firstly, before we get any further into this section, I want to reiterate that while CoffeeScript’s syntax is often identical with JavaScript’s, it’s not a superset, and therefore some JavaScript keywords, such as function and var, aren’t permitted, and will throw syntax errors. If you’re writing a CoffeeScript file, it needs to be pure CoffeeScript; you can’t intermingle the two languages.

Why isn’t CoffeeScript a superset? Well, the very fact that white space is significant in CoffeeScript programs prevents it from being a superset. And, once that decision’s been made, the team decided you might as well go the full hog and deprecate some JavaScript keywords and features in the name of simplicity and in an effort to reduce many commonly occurring bugs.