app.js

var express = require('express'),
    app = express(),
    server = require('http').createServer(app),
    io = require('socket.io').listen(server);
    users = {};


server.listen(1111);
console.log('Listning on port 1111....');
app.get('/',function(req,res){
   res.sendFile(__dirname + '/index.html');
});

io.sockets.on('connection',function(socket){

	socket.on('new user',function(data,callback){
		if(data in users){
			callback(false);
		} else {
			callback(true);
			socket.nickname = data;
			users[socket.nickname] = socket;
			updateNicknames();
		}
	});

	function updateNicknames(){
		io.sockets.emit('usernames',Object.keys(users));
	}

   socket.on('send message',function(data,callback){
   	var msg = data.trim();
   	if(msg.substr(0,3) === '/w '){
   		msg = msg.substr(3);
   		var ind = msg.indexOf(' ');
   		if(ind !== -1){
   			var name = msg.substring(0, ind);
   			var msg = msg.substring(ind + 1);
   			if(name in users){
   				users[name].emit('whisper',{msg: msg, nick: socket.nickname});
   				console.log('wisper!');
   			}else {
   				console.log('Error! Enter the valid user');
   			}
   		}else{
   			callback('Error! please enter msg for your whisper');
   		}
   		
   	} else {
   		io.sockets.emit('new message',{msg: msg, nick: socket.nickname});
   	}
   });
   socket.on('disconnect',function(data){
   	if(!socket.nickname) return;
   	delete users[socket.nickname];
   	updateNicknames();
   });
});