如何使用post请求下载文件

使用get请求下载文件非常简便，但是get请求的url有长度和大小的限制，所以当请求参数非常多时无法满足需求，所以改成post请求
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);
}