Question

What are the fundamental differences between utilizing CoffeeScript extends vs. Backbone.js extend?

For example, how is

class User extends Backbone.Model

different from

User = Backbone.Model.extend()

Answer 1

The two are intended to be equivalent. To quote the Backbone.js changelog:

0.3.0: Backbone classes may now be seamlessly inherited by CoffeeScript classes.

Both CoffeeScript’s Child extends Parent and Backbone’s Child = Parent.extend() do three important things:

1. (Most important) They set Child.prototype to new ctor, where ctor is a function whose prototype is Parent.prototype. That establishes prototypal inheritance.
2. They copy all of Parent‘s static properties onto Child.
3. They set Child.__super__ = Parent. This is mainly to support CoffeeScript’s Ruby-like super keyword in Child‘s methods.