code: function(fileName) {
                  let file = assets[fileName] || {};
                  fileName = basePath + "/" + fileName.replace(/\\/g, '/');
                  let key = path.posix.join(uploadPath, fileName);
  
                  return new Promise((resolve, reject) => {
                      let begin = Date.now();
                      cos.putObject(
                          {
                              Bucket: bucket,
                              Region: region,
                              Key: key,
                              Body: fs.createReadStream(file.existsAt),
                              ContentLength: fs.statSync(file.existsAt).size
                          },
                          function(err, body) {
                              uploadedFiles++;
                              spinner.text = tip(uploadedFiles, totalFiles);
  
                              if (err) return reject(err);
                              body.duration = Date.now() - begin;
                              resolve(body);
                          }
                      );
                  });
              }
docs: Perform upload to cos