backbone 'changes' collection

changes_collection.js

var Book = Backbone.Model.extend({});

var Library = Backbone.Collection.extend({
  model: Book,
  url: '/books',
  
  initialize: function() {
      this.on('add', function(model) {
        console.log('added: ', model);
      })
  }
});

var LibraryChanges = Backbone.Collection.extend({
  initialize: function(collection, options) {
    this.collection = options.collection;
    console.log('url: ', this.collection.url);
    console.log('book 555: ', this.collection.get(555));
    this.collection.add({ name:'Agile Web Development' });
  }  
});

var library = new Library([{ id:555, name:'Programming Your Home' }]);

var libraryChanges = new LibraryChanges([],{ collection:library });