Every Collection class has a model property, which defaults to Backbone.Model. You can set this property by providing it as an option when you use extend to create your Collection subclass:
var Cats = Backbone.Collection.extend({model: Cat});
var cats = new Cats(); // cats.model == CatHowever, this model property doesn't actually limit the type of Model a Collection can hold, and in fact, any Collection can hold any type of Model:
var Cat = Backbone.Model.extend();
var Cats = Backbone.Collection.extend({model: Cat});
var Dog = Backbone.Model.extend();
var snoopy = new Dog({name: 'Snoopy'});
var cartoonCats = new Cats([snoopy]);
cartoonCats.models[0] instanceof Dog; // trueThis is because the model property of a Collection is only used when new Models are created through the Collection. One way in which this can happen is when the Collection is initialized with an array of attributes, as shown in the following example:
var snoopyAttributes = {id: 'dog1', name: 'Snoopy...