var express = require('express');
var app = express();
var serv = require('http').Server(app);

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

serv.listen(2000);
console.log("Server started.");


var io = require('socket.io')(serv,{});
io.sockets.on('connection', function(socket){
	console.log('socket connection');

	socket.on('happy',function(data){
		console.log('happy because ' + data.reason);
	});

	socket.emit('serverMsg',{
		msg:'hello',
	});

});



<script src="https://cdn.socket.io/socket.io-1.4.5.js"></script>
<script>
	var socket = io();

	var random = Math.random();

	var happy = function(){
		socket.emit('happy',{
			reason:'its my birthday' + random
		});
	}

	socket.on('serverMsg',function(data){
		console.log(data.msg);
	});


</script>

<button onclick="happy()">Happy</button>