JavaScript Fetch API를 사용하여 파일 업로드를 어떻게 마스터할 수 있습니까?

<form>
  <div>
    <label>Select file to upload</label>
    <input type="file">
  </div>
  <button type="submit">Convert</button>
</form>

document.querySelector('form').addEventListener('submit', (event) => {
  // Prevent default form submission
  event.preventDefault();
  
  // Retrieve the selected file
  const input = event.target.querySelector('input[type="file"]');
  
  // Construct the request body
  const formData = new FormData();
  formData.append('file', input.files[0]);
  
  // Submit the request
  fetch('/files', {
    method: 'POST',
    body: formData
  }).then(/* perform necessary actions */);
});

const formData = new FormData();
formData.append('file', input.files[0]);
formData.append('user', 'username');

fetch('/files', {
  method: 'POST',
  body: formData
})
.then(/* handle the response as desired */);