Demonstrate the functionalities of fs module in asynchronous mode.

const fs = require('fs');

fs.writeFile('async.txt', 'This is written using writeFile (Async)', (err) => {
  if (err) throw err;
  console.log('File created and written successfully.');

  fs.readFile('async.txt', 'utf8', (err, data) => {
    if (err) throw err;
    console.log('File content:', data);

    fs.appendFile('async.txt', '\nThis is an additional line (Async)', (err) => {
      if (err) throw err;
      console.log('Content appended.');

      fs.unlink('async.txt', (err) => {
        if (err) throw err;
        console.log('File deleted.');
      });
    });
  });
});