这是一个由5部分组成的backbone.js hello world教程/应用程序。https://web.archive.org/web/20180317062059/http://arturadib.com/hello-backbonejs/docs/3.html在第3部分中，作者演示了如何使用集合和模型来存储数据，以及如何将更改绑定到视图。
大部分我都懂除了这句

this.collection.bind('add', this.appendItem); // collection event binder

这个'bind'仅仅是绑定上下文，还是作为一个'event'，在添加模型的任何时候都调用appendItem？
我问一下，因为在ListView的render方法中，它是显式调用appendItem方法的，那么为什么它绑定到'add'

_(this.collection.models).each(function(item){ // in case collection is not empty
    self.appendItem(item);
  }, this);

有人能解释一下代码是如何工作的吗？我看了文档，但没有找到以这种方式使用绑定的解释。
完整代码

(function($){
¶
Item class: The atomic part of our Model. A model is basically a Javascript object, i.e. key-value pairs, with some helper functions to handle event triggering, persistence, etc.

  var Item = Backbone.Model.extend({
    defaults: {
      part1: 'hello',
      part2: 'world'
    }
  });      

¶
List class: A collection of Items. Basically an array of Model objects with some helper functions.

  var List = Backbone.Collection.extend({
    model: Item
  });

  var ListView = Backbone.View.extend({
    el: $('body'),
    events: {
      'click button#add': 'addItem'
    },
¶
initialize() now instantiates a Collection, and binds its add event to own method appendItem. (Recall that Backbone doesn't offer a separate Controller for bindings...).

    initialize: function(){
      _.bindAll(this, 'render', 'addItem', 'appendItem'); // remember: every function that uses 'this' as the current object should be in here

      this.collection = new List();
      this.collection.bind('add', this.appendItem); // collection event binder

      this.counter = 0;
      this.render();      
    },
    render: function(){
¶
Save reference to this so it can be accessed from within the scope of the callback below

      var self = this;      
      $(this.el).append("<button id='add'>Add list item</button>");
      $(this.el).append("<ul></ul>");
      _(this.collection.models).each(function(item){ // in case collection is not empty
        self.appendItem(item);
      }, this);
    },
¶
addItem() now deals solely with models/collections. View updates are delegated to the add event listener appendItem() below.

    addItem: function(){
      this.counter++;
      var item = new Item();
      item.set({
        part2: item.get('part2') + this.counter // modify item defaults
      });
      this.collection.add(item); // add item to collection; view is updated via event 'add'
    },
¶
appendItem() is triggered by the collection event add, and handles the visual update.

    appendItem: function(item){
      $('ul', this.el).append("<li>"+item.get('part1')+" "+item.get('part2')+"</li>");
    }
  });

  var listView = new ListView();
})(jQuery);