我是一个backbone.js初学者，看看下面的例子，我想知道这个函数到底是：appendItem，它传递了参数：item，它在哪里以及如何传递那个arg？
(function($){
var Item = Backbone.Model.extend({
defaults: {
part1: 'hello',
part2: 'world'
}
});
var List = Backbone.Collection.extend({
model: Item
});
var ItemView = Backbone.View.extend({
tagName: 'li',
initialize: function(){
_.bindAll(this, 'render');
return this.render();
},
render: function(){
$(this.el).html('<span>'+this.model.get('part1')+this.model.get('part2')+'</span>');
return this;
}
});
var ListView = Backbone.View.extend({
el: $('body'),
events: {
'click button#add': 'addItem'
},
initialize: function(){
_.bindAll(this, 'render', 'addItem', 'appendItem');
this.collection = new List();
this.collection.bind('add', this.appendItem);
this.counter = 0;
return this.render();
},
render: function(){
var self = this;
$(this.el).append("<button id='add'>Add list item</button>");
$(this.el).append("<ul></ul>");
_(this.collection.models).each(function(item){
self.appendItem(item);
}, this);
return this;
},
addItem: function(){
this.counter++;
var item = new Item();
item.set({
part2: item.get('part2') + this.counter
});
this.collection.add(item);
},
appendItem: function(item){
var itemView = new ItemView({
model: item
});
$('ul', this.el).append(itemView.el);
}
});
var listView = new ListView();
})(jQuery);