app.js

var http = require('http');
var url = require('url');
var path = require('path');
var fs = require('fs');

var server = http.createServer(function(req, res) {
  console.log(`${req.method} ${req.url}`);

  // parse URL
  const parsedUrl = url.parse(req.url);
  // extract URL path
  let pathname = `.${parsedUrl.pathname}`;
  // based on the URL path, extract the file extention. e.g. .js, .doc, ...
  const ext = path.parse(pathname).ext;
  // maps file extention to MIME typere
  const map = {
    '.html': 'text/html',
    '.js': 'text/javascript',
    '.css': 'text/css'
  };

  fs.exists(pathname, function (exist) {
    if(!exist) {
      // if the file is not found, return 404
      res.statusCode = 404;
      res.end(`File ${pathname} not found!`);
      return;
    }

    // if is a directory search for index file matching the extention
    if (fs.statSync(pathname).isDirectory()) pathname += '/index' + ext;

    // read file from file system
    fs.readFile(pathname, function(err, data) {
      if (err) {
        res.statusCode = 500;
        res.end(`Error getting the file: ${err}.`);
      } else {
        // if the file is found, set Content-type and send data
        res.setHeader('Content-type', map[ext] || 'text/plain');
        res.end(data);
      }
    });
  });
});

var io = require('socket.io').listen(server);

io.sockets.on('connection', function(socket) {
  console.log('Client connected');

  socket.on('timer', function(message) {
    console.log(`-> timer ${message}`);
    io.sockets.emit('timer', message);
  });

  socket.on('message', function(message) {
    console.log(`-> message ${message}`);
    io.sockets.emit('message', message);
  });
});

server.listen(8080);