CoffeeScript classes are a great way to organize your code, and work just fine on their own. Sometimes, though, you'll be using a JavaScript framework that provides (among other things) its own class structures. It's usually possible to build these classes in CoffeeScript, but the exact mechanism will vary depending on the framework.
We'll look at two popular frameworks here. If you have another framework you wish to use, it's likely that it will fall into one of these two categories. In the first, we use the full CoffeeScript class system, and integrate it with the framework through standard JavaScript functionality. In the second, we use the framework's system to define classes, but still make use of syntactic CoffeeScript sugar when we're filling in the classes' behavior.