/*
 模型用于封装与应用程序的业务逻辑相关的数据以及对数据处理的方法。模型有对数据直接访问的权利。
 模型不依赖 "视图" 和 "控制器", 也就是说 模型它不关心页面如何显示及如何被操作.
*/
function Mode(elems) {
  // 所有元素
  this._elems = elems;
 
  // 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._listeners[i](this._observer,objs);
    }
  }
};
 
/*
 * 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);
  }
};

<select id="list" size="10" style="width: 10rem">select>br/>
<button id="plusBtn"> + button>
<button id="minusBtn"> - button>

$(function () {
  var model = new Mode(['PHP', 'JavaScript']),
   view = new View(model, {
    'list' : $('#list'), 
    'addButton' : $('#plusBtn'), 
    'delButton' : $('#minusBtn')
    }),
    controller = new Controller(model, view);    
    view.show();
});

// 添加按钮绑定事件
this._elements.addButton.click(function(e){
  that.addButtonClicked.notify();
});

this._view.addButtonClicked.attach(function(){
  that.addItem();
});

addItem: function(){
  var item = window.prompt('Add item:', '');
  if (item) {
    this._model.addItem(item);
  }
}

// 增加一项
addItem: function(elem) {
  this._elems.push(elem);
  this.itemAdd.notify({elem:elem});
},

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