app.js

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

app.get('/', function(req, res){
      res.sendfile('index.html');
});
io.on('connection', function(socket){
      console.log('A user connected');

      setTimeout(function(){
          socket.emit('testerEvent', { description: 'A custom event named testerEvent!'});
                }, 4000);

        //Whenever someone disconnects this piece of code executed
        socket.on('disconnect', function () {
                console.log('A user disconnected');
                  });
        socket.on('clientEvent', function(data){
                console.log(data);
                  });
});

http.listen(3000, function(){
      console.log('listening on *:3000');
});