In this chapter, we explored how JavaScript's native class system works and how the new, this, and prototype keywords/properties form the basis of it. We also learned how Backbone's extend method makes creating new subclasses much more convenient as well as how to use apply and call to invoke parent methods (or when providing callback functions) to preserve the desired this method. Finally, we looked at a number of ways in which Underscore, one of Backbone's dependencies, can solve common problems. In the next chapter, we'll dive into the first of the four Backbone classes, Model. We'll learn how to use Model to organize our data on the client side and to exchange this data to and from our remote server.