server.js

var express = require ("express");
var app = express();
var server = require ('http').createServer(app);
var io = require('socket.io').listen(server);
users = [];
connections = [];

server.listen(process.env.PORT || 3000);
console.log("Server running");

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

io.sockets.on('connection', function(socket){
    connections.push(socket);
    console.log('connected: %s sockets connected',connections.length);

    socket.on('disconnect',function(data){
    users.splice(users.indexOf(socket.username),1);
    updateUsernames();
    connections.splice(connections.indexOf(socket),1);
    console.log('Disconnected: %s sockets connected',connections.length);
	});

	socket.on('send message',function(data){
		io.sockets.emit('new message',{msg:data, user: socket.username});
	});

    socket.on('new user',function(data,callback){
        callback(true);
        socket.username = data;
        users.push(socket.username);
        updateUsernames();
    });

    function updateUsernames(){
        io.sockets.emit('get users', users);
    }

});