// --------------------------------------------------

function Subject(){}

Subject.prototype.add = function(obj)

{

    if(typeof(obj.update) === "function")

    {

        this.objects.push(obj);

        return true;

    }

    return false;

}

Subject.prototype.notify = function(subject)

{

    for(var i in this.objects)

    {

        obj = this.objects[i];

        obj.update(subject);

    }

}

// --------------------------------------------------

function Subject1()

{

    Subject.call(this);

    this.objects = new Array();

    this.message = "hello";

}

Subject1.prototype = new Subject()

Subject1.prototype.update = function(s)

{

    if (s != null)

        this.message = s;

    this.notify(this);

}

// --------------------------------------------------

function Observer(){}

Observer.prototype.update = function(subject)

{

    alert(subject.message);

}

// --------------------------------------------------

var subject = new Subject1();

var observer = new Observer();

subject.add(observer);

subject.update();

subject.update("same world");