Node.js - More flexible HTTP server#2 (lab tutorial)

app.js

const http = require('http');
const fs = require('fs');

const server = http.createServer((req, res) => {
  // -------- more flexible way ---------

  // Build file path
  let filePath = path.join(
    __dirname,
    'public',
    req.url === '/' ? 'index.html' : req.url
  );

  // get file extension
  let extname = path.extname(filePath);

  // initial content type;
  let contentType = 'text/html';
  switch (extname) {
    case '.js':
      contentType = 'text/javascript';
      break;
    case '.css':
      contentType = 'text/css';
      break;
    case '.json':
      contentType = 'application/json';
      break;
    case '.png':
      contentType = 'image/png';
      break;
    case '.jpg':
      contentType = 'image/jpg';
      break;
  }

  // Check if contentType is text/html but no .html file extension
  if (contentType == "text/html" && extname == "") filePath += ".html";

  // log the filePath
  console.log(filePath);

  // Read file
  fs.readFile(filePath, (err, content) => {
    if (err) {
      if (err.code == 'ENOENT') {  // Page not found
        fs.readFile(path.join(__dirname, 'public', '404.html'), 
        (err, content) => {
          res.writeHead(200, { 'Content-Type': 'text/html' });
          res.end(content, 'utf8');
        })
      } else {
        // Some server errors: 500
        res.writeHead(500);
        res.end('Server error: ' + err.code);
      }
    } else {
      // Success request
      res.writeHead(200, { 'Content-Type': contentType });
      res.end(content, 'utf8');
    }
  })
});

// set port number to run to PORT or 5000
const PORT = process.env.PORT || 5000;
server.listen(PORT, () => {
  console.log('Server is running on port ', PORT);
});