router.get('/download', (req, res) => { 
  let filePath = path.join(__dirname, `../${basePath}/${data.path}`) 
  let stats = fs.statSync(filePath);
  if (stats.isFile()) {
  
     /******  方法一  ********/ 
    // res.download(filePath, function (err) {
    //  if (err) { console.log(err); }
    // });
    try {
      let filePath = '/test.txt';
      let fileName = path.basename(filePath);
      res.download(filePath, fileName);
    } catch (error) {
      return res.status(500).send({
        result: 'error',
        message: `Failed to download file: ${error.message}`
      })
    }
     
    /******  方法二  ********/ 
    res.set({
      'Content-Type': 'application/octet-stream',
      // 'Content-Disposition': 'attachment; filename=' + fileName,
      'Content-Length': stats.size
    });
    fs.createReadStream(filePath).pipe(res);
  } else {
    res.json({ code: 500, message: "文件不存在！" });
  }