如何使用post請求下載文件

使用get請求下載文件非常簡便，但是get請求的url有長度和大小的限制，所以當請求參數非常多時無法滿足需求，所以改成post請求
const res = await fetch('xxxxxxxxx', {
  method: 'post',
  body: JSON.stringify(params),
  credentials: 'include',
  headers: {
    'Cache-Control': 'max-age=0',
    'Pragma': 'no-cache',
    'Content-Type': 'application/json;charset=UTF-8',
    'x-requested-with': 'fetch'
  }
  });
  const blob = await res.blob();
  if ('download' in document.createElement('a')) {
  var a = document.createElement('a');
  a.style.display = 'none';
  var url = window.URL.createObjectURL(blob);
  var filename = decodeURIComponent(res.headers.get('Content-Disposition'));
  a.href = url;
  a.download = filename;
  document.body.appendChild(a);
  a.click();
  window.URL.revokeObjectURL(url);
  document.body.removeChild(a);
  } else {
  navigator.msSaveBlob(blob);
}