javascript实现观察者模式

/*---------------------------

defined observer

----------------------------*/

function Observer()

{

}

Observer.prototype.update = function(context)

{

alert(context);

}

function ConcreteObserver()

{

Observer.call(this);

}

ConcreteObserver.prototype.update = function(context)

{

alert("ConcreteObserver response " + context);

}

/*---------------------------

defined ObserverCollection

----------------------------*/

function ObserverCollection()

{

this._observers_ = new Array();

}

ObserverCollection.prototype.add = function(observer)

{

this._observers_.push(observer);

}

ObserverCollection.prototype.count = function()

{

return this._observers_.length;

}

ObserverCollection.prototype.getAt = function(index)

{

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

{

return this._observers_[index];

}

return undefined;

}

/*---------------------------

defined Subject

----------------------------*/

function Subject(name)

{

this.name = name;

this._obs_ = new ObserverCollection();

}

Subject.prototype.add = function(ob)

{

if (ob.update)

{

this._obs_.add(ob);

}

}

Subject.prototype.nameChanged = function()

{

var ob;

for(var i=0; i < this._obs_.count(); i++)

{

ob = this._obs_.getAt(i);

ob.update(this.name);

}

};

Subject.prototype.setName = function(newName)

{

if (this.name != newName)

{

this.name = newName;

this.nameChanged();

}

}

var sub = new Subject("jjy");

sub.add(new Observer());

sub.add(new ConcreteObserver());

sub.setName("Jack");

sub.setName("HongYing");