Step 2 - Creating a module bundler with Hot Module Replacement

index.js

// some code here

// websocket connection for notifying browser
var io = require('socket.io')(http);

// some code here

var processFiles = function(callback) {
  // some code here
  md.pipe(JSONStream.stringify())
  // some code here
  .on('end', function() {
    fs.writeFile('dist/bundle.js', bundleStr, 'utf8', function() {
      console.log('Bundle file written...');
      if (typeof callback === 'function') {
        callback();
      }
    });
  });

  md.end({ file: path.join(__dirname, args[0]) });
};

// watch app folder for changes
fs.watch('app', function(event, fileName) {
  // create bundle with new changes
  processFiles(function() {
    // notify the browser of the change
    io.emit('file-change', { id: path.join('app', fileName) });
  });
});

// some code here