//模拟一个目标可能拥有的一些列依赖

 function ObserverList() {

 this.observerList = [];

 };

 //添加一个观察者

 ObserverList.prototype.Add = function (obj) {

 return this.observerList.push(obj);

 };

 //清除所有观察者

 ObserverList.prototype.Empty = function () {

 this.observerList = [];

 };

 //获得所有观察者的数量

 ObserverList.prototype.Count = function () {

 return this.observerList.length;

 };

 //获取某个指定的观察者

 ObserverList.prototype.Get = function (index) {

 if (index > -1 && index < this.observerList.length) {

 return this.observerList[index];

 }

 };

 //插入一个观察者

 ObserverList.prototype.Insert = function (obj, index) {

 var pointer = -1;

 if (index === 0) {

 this.observerList.unshift(obj);

 pointer = index;

 } else if (index == this.observerList.length) {

 this.observerList.push(obj);

 pointer = index;

 }

 return pointer;

 };

 //从某个位置开始查找特定的观察者并返回观察者的索引值

 ObserverList.prototype.IndexOf = function (obj, startIndex) {

 var i = startIndex, pointer = -1;

 while (i < this.observerList.length) {

 if (this.observerList[i] == obj) {

 pointer = i;

 } i++;

 }

 return pointer;

 };

 //移除某个特定索引的观察者（如果存在）

 ObserverList.prototype.RemoveIndexAt = function (index) {

 if (index == 0) {

 this.observerList.shift();

 } else if (index == this.observerList.length - 1) {

 this.observerList.pop();

 }

 };

 //扩展对象

 function extend(obj, extension) {

 console.log(obj);

 for (var k in obj) {

 console.log(k);

 extension[k] = obj[k]

 }

 };

 //模拟一个目标对象，并模拟实现在观察者列表上添加、删除和通知观察者的能力

 function Subject() {

 this.observers = new ObserverList();

 };

 //目标添加一个观察者

 Subject.prototype.AddObserver = function (observer) {

 this.observers.Add(observer);

 };

 //目标对象移除某个观察者

 Subject.prototype.RemoveObserver = function (observer) {

 this.observers.RemoveIndexAt(this.observers.IndexOf(observer, 0));

 };

 Subject.prototype.RemoveAllObserver = function () {

 this.observers = [];

 }

 //模拟实现通知功能

 Subject.prototype.Notify = function (context) {

 var observerCount = this.observers.Count();

 for (var i = 0; i < observerCount; i++) {

 this.observers.Get(i).Update(context);

 }

 };

 //模拟创建一个观察者

 function Observer() {

 this.Update = function () {

 };

 }

 var controlCheckbox = document.getElementById("mainCheckBox");

 var removerObserver = document.getElementById("removerAllObserver");

 var addBtn = document.getElementById("addNewObserver");

 var container = document.getElementById("observerContainer");

 extend(new Subject(), controlCheckbox);

 controlCheckbox["onclick"] = Function("controlCheckbox.Notify(controlCheckbox.checked)");

 addBtn["onclick"] = AddNewObserver;

 function AddNewObserver() {

 var check = document.createElement("input");

 check.type = "checkbox";

 extend(new Observer(), check);

 check.Update = function (value) {

 this.checked = value;

 };

 controlCheckbox.AddObserver(check);

 container.appendChild(check);

 }