server.js

var express = require('express');
var app = express();
var server = require('http').createServer(app);
var io = require('socket.io').listen(server);
var mongoose = require('mongoose');
//var nicknames = [];
var users = {};


mongoose.connect('mongodb://localhost/testdb', function(err){
	if(err){
		console.log(err);
	} else {
		console.log('coneected to mongodb');
	}
});

var Schema = mongoose.Schema;
var chatSchema = new Schema({
	nickname : String,
	msg : String,
	created : { type : String, default : Date.now }
});
var Chat = mongoose.model('chat', chatSchema);


app.get('/', function(req, res){
	res.sendFile(__dirname + '/index.html');
});

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

	Chat.find({}, function(err, docs){
		if(err) throw err;
		socket.emit('load old msgs', docs);
	});

	socket.on('new user', function(data, callback){
		//if(nicknames.indexOf(data) != -1){
		if(data in users){
			callback(false);
		} else {
			callback(true);
			socket.nickname = data;
			//nicknames.push(socket.nickname);
			users[socket.nickname] = socket;
			updateNickname();
		}
	});

	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, nickname : socket.nickname });
				} else {
					callback('Error : Enter a valid user!');
				}
			} else {
				callback('Error : Please enter message!!');
			}
		} else {
			new Chat({ 'nickname' : socket.nickname, 'msg' : data }).save(function(err){
				if(err) throw err;
				io.sockets.emit('new message', { msg : data, nickname : socket.nickname });
				//socket.broadcast.emit('new message', data);
			});
		}
	});

	socket.on('disconnect', function(data){
		if(!socket.nickname) return;
		//nicknames.splice(nicknames.indexOf(socket.nickname),1);
		delete users[socket.nickname];
		updateNickname();
	});

	function updateNickname(){
		//io.sockets.emit('username', nicknames);
		io.sockets.emit('username', Object.keys(users));
	}
});

server.listen(3000, function(){
	console.log('server is up!');
});