Observer.js

//Define an Observer class
function Observer(name, updateFn) {
	this.name = name;
	this.updateFn = updateFn;
}
			
//Create an instance of Observer class 
observerObj = new Observer("observer1", function(msg) {	console.log(msg); });

//Create an instance of the Subject and provide the observer object
tObject = new Twitter("sagarganatra",observerObj);

Subject.js

/*
 * Define a generic class Subject with two methods
 * 'addObserver' and 'notifyObserver'
*/
function Subject() {
	this.observerList = [];
}

Subject.prototype.addObserver = function(observerObj) {
	this.observerList.push(observerObj)
}

Subject.prototype.notifyObserver = function(msg) {
	for (var i = 0, length = this.observerList.length; i < length; i++) {
		this.observerList[i]['updateFn'](msg);
	}
}

Twitter.js

/*
 * Define a Twitter class which extends the Subject class
*/
function Twitter(handlerName,observerObj) {
	//Call the parent class - Subject
	Subject.call(this);

	//Handler name is the username for which tweets has to be retrieved
	this.handlerName = handlerName;

	//add the observer object
	this.addObserver(observerObj);

	//fetch the status messages	
	this.init();			
}

Twitter.prototype = Object.create(Subject.prototype);

//Define the init method that will fetch the status messages
Twitter.prototype.init = function() {
	parent = this;
	$.ajax({
		url: 'http://twitter.com/statuses/user_timeline/' + parent.handlerName + '.json?callback=?',
		success: function(data) {
		//iterate over the list of tweets
		$.each(data,function(index,value)
		{
			var message = value.text;

			//ignore the reply messages i.e. messages that start with '@'
 			if(message[0] != '@')
 			{
 				//Check whether the status message contains a link
 				if((index=message.indexOf('http://')) > 0) 
 				{
 					substr1 = message.substr(index);
 					nextIndex = substr1.indexOf(' ');
 					substr2 = (nextIndex > 0)? substr1.substr(0,substr1.indexOf(' ')):substr1.substr(0);
 					pos1 =  message.indexOf(substr2);
 					pos2 = pos1 + substr2.length;
 					newMessage = [message.slice(0,pos1),'<a href='+ substr2+ ' target="_blank" >' + substr2 + '</a>',message.slice(pos2)].join('');

 					//notify the Observer of the new message
 					parent.notifyObserver(newMessage);
 				}
 				else  {
 					parent.notifyObserver(message);
 				}	 
 			}
	 	});
	},

	//if there is an error, throw an Error message
	error: function(data) {
		parent.notifyObserver("Error");
	},

	dataType: 'json'
	});
}