XMLHttpRequest 获取响应头不完整 - 《learning》

XMLHttpRequest 跨域请求CORS会出现http响应头不全的情况，但是在chrome中正常显示，js获取不全。
需要在服务端增加配置响应的请求头。
response.setHeader("Access-Control-Expose-Headers","Content-Disposition");
即可拿到响应头

async downloadFile ( url :string ,fileName?:string ){
  const req = new XMLHttpRequest();
  const token = 'get token'
  req.open('get', url);
  req.setRequestHeader('token', token);
  req.responseType = 'blob';
  req.onreadystatechange = ()=>{
    if (req.readyState === 4 && req.status === 200) {
      const headerfileName = req.getResponseHeader('Content-Disposition') ;
      if(headerfileName){
        fileName = decodeURI(headerfileName.replace('attachment;filename=', ''));
      }
      const blob = new Blob([req.response]);
      const blobUrl = window.URL.createObjectURL(blob);
      const a = document.createElement('a');
      a.href = blobUrl;
      a.download = fileName ;
      a.click();
    }else{
      console.log('服务异常。');
    }
  }
  req.send();
}