app.js

// Setting up libraries and configuration
var express = require('express');		// The require() function includes the code for Express
var app = express();					// Initialize the Express library
var http = require('http').Server(app);	// Initialize an HTTP server
var io = require('socket.io')(http);	// Include and initialize SocketIO
var port = process.env.PORT || 8000;	// Set the default port number to 8000, or use Heroku's settings (process.env.PORT)

// Use Express to serve everything in the "public" folder as static files
app.use(express.static('public'));

// Activate the server and listen on our specified port number
http.listen(port, function() {
	// Display this message in the server console once the server is active
	console.log('Listening on port ' + port);
});

// When a user connects over websocket,
io.on('connection', function(socket) {

	// Display this message in the server console
	console.log('A user connected!');

	// When the server receives a message named "new line",
	socket.on('new line', function(data){
		// Display the received data in the server console
		console.log(data);
		// Send the data in a message called "new line" to every connected client EXCEPT the client who sent this initial "new line" message
		socket.broadcast.emit('new line', data);
	});

});	// End of SocketIO code