JavaScript는 어떻게 서버측과 클라이언트측 모두에서 파일을 읽고 쓸 수 있습니까?

const fs = require('fs');

// Read a file
fs.readFile('file.txt', 'utf8', (err, data) => {
  if (err) throw err;
  console.log(data);
});

// Write a file
fs.writeFile('file.txt', 'Hello world!', err => {
  if (err) throw err;
  console.log('File has been written successfully.');
});

const fileInput = document.getElementById('file-input');

fileInput.addEventListener('change', e => {
  const file = e.target.files[0];

  // Read a file
  const reader = new FileReader();
  reader.onload = () => {
    console.log(reader.result);
  };
  reader.readAsText(file);

  // Write a file (client-side)
  const filename = 'file.txt';
  const fileContent = 'Hello world!';

  const blob = new Blob([fileContent], { type: 'text/plain' });
  const url = URL.createObjectURL(blob);

  const a = document.createElement('a');
  a.href = url;
  a.download = filename;
  a.click();
});