// 被选中元素的索引
this._selectedIndex = -1;

// 增加一项
this.itemAdd = new Event(this);

// 删除一项
this.itemRemoved = new Event(this);

this.selectedIndexChanged = new Event(this);
}

Mode.prototype = {

constructor: 'Mode',// 获取所有的项
getItems: function(){
return [].concat(this._elems);
},// 增加一项
addItem: function(elem) {
this._elems.push(elem);
this.itemAdd.notify({elem:elem});
},// 删除一项
removeItem: function(index) {
var item = this._elems[index];
this._elems.splice(index,1);
this.itemRemoved.notify({elem:item});

if(index === this._selectedIndex) {
  this.setSelectedIndex(-1);
}

},getSelectedIndex: function(){
return this._selectedIndex;
},setSelectedIndex: function(index){
var prevIoUsIndex = this._selectedIndex;
this._selectedIndex = index;
this.selectedIndexChanged.notify({prevIoUs : prevIoUsIndex});
}
};
/
下面是观察者模式类,它又叫发布---订阅模式;它定义了对象间的一种一对多的关系，
让多个观察者对象同时监听某一个主题对象，当一个对象发生改变时，所有依赖于它的对象都将得到通知。
/
function Event(observer) {
this._observer = observer;
this._listeners = [];
}
Event.prototype = {
constaructor: 'Event',attach : function(listeners) {
this._listeners.push(listeners);
},notify: function(objs){
for(var i = 0,ilen = this._listeners.length; i ) {
this._listenersi;
}
}
};

/*

• 视图显示模型数据，并触发UI事件。
  */
  function View(model,elements){
  this._model = model;
  this._elements = elements;

this.listModified = new Event(this);
this.addButtonClicked = new Event(this);
this.delButtonClicked = new Event(this);
var that = this;

// 绑定模型监听器
this._model.itemAdd.attach(function(){
that.rebuildList();
});
this._model.itemRemoved.attach(function(){
that.rebuildList();
});

// 将监听器绑定到HTML控件上
this._elements.list.change(function(e){
that.listModified.notify({index: e.target.selectedIndex});
});
// 添加按钮绑定事件
this._elements.addButton.click(function(e){
that.addButtonClicked.notify();
});
// 删除按钮绑定事件
this._elements.delButton.click(function(e){
that.delButtonClicked.notify();
});
}
View.prototype = {
constructor: 'View',show: function(){
this.rebuildList();
},rebuildList: function(){
var list = this._elements.list,items,key;
list.html("");
items = this._model.getItems();
for(key in items) {
if(items.hasOwnProperty(key)) {
list.append('' +items[key]+ '');
}
}
this._model.setSelectedIndex(-1);
}
};
/
控制器响应用户操作，调用模型上的变化函数
负责转发请求，对请求进行处理
/
function Controller(model,view) {
this._model = model;
this._view = view;
var that = this;

this._view.listModified.attach(function(sender,args){
that.updateSelected(args.index);
});
this._view.addButtonClicked.attach(function(){
that.addItem();
});
this._view.delButtonClicked.attach(function(){
that.delItem();
});
}
Controller.prototype = {
constructor: 'Controller',addItem: function(){
var item = window.prompt('Add item:','');
if (item) {
this._model.addItem(item);
}
},delItem: function(){
var index = this._model.getSelectedIndex();
if(index !== -1) {
this._model.removeItem(index);
}
},updateSelected: function(index){
this._model.setSelectedIndex(index);
}
};