Node.js 未处理的拒绝错误

Question

我的代码中出现 Unhandled Rejection 错误，但跟踪不会告诉我是什么原因造成的。我认为这webp.cwebp是导致问题的电话。当我运行代码时，我成功转换了图像和日志状态，然后遇到了未处理的拒绝。似乎我没有进入最后两个.then(()块，因为没有从它们记录控制台消息。

如何正确处理拒绝错误以避免此错误？我试过status在resolve()andreject()语句中插入和删除，但它似乎没有修复它。

 // Download image file from Google Cloud Storage bucket.
 return file.download({ destination: tempLocalFilename })
  .catch((err) => {
    console.error('Failed to download file.', err);
    return Promise.reject(err);
  })
  .then(() => {
    console.log(`Image ${file.name} has been downloaded to ${tempLocalFilename}.`);

    // Convert PNG to webp using webp-converter.
    return new Promise( (resolve, reject) => {
        webp.cwebp(tempLocalFilename, newLocalFilename, "-q 80", status => {
             console.log(status);

             if (status === '100') {
                 resolve();
             } else {
                 reject(status);
             }
           }
         );
       });
  })
  .then(() => {
    console.log(`Image ${file.name} has been converted.`);

    // Upload the converted image back into the bucket.
    return file.bucket.upload(newLocalFilename, { destination: file.name })
      .catch((err) => {
        console.error('Failed to upload converted image.', err);
        return Promise.reject(err);
      });
  })
  .then(() => {
    console.log(`Converted image has been uploaded to ${file.name}`);

    // Delete the temporary file.
    return new Promise((resolve, reject) => {
      fs.unlink(tempLocalFilename, (err) => {
        if (err) {
          reject(err);
        } else {
          resolve();
        }
      });
    });
  });

Answer 1

问：我收到未处理的拒绝错误，我该如何正确处理拒绝错误？

A：就像评论已经说过的那样，a.catch(...)将阻止您的异常冒泡成为unhandled rejection error.

或者，您也可以为每个.then(...)子句插入拒绝处理函数。也就是说，对于每个.then()它应该采用 2 个函数，一个用于快乐路径，另一个用于坏路径。

例如

  return new Promise( (resolve, reject) => {
        webp.cwebp(tempLocalFilename, newLocalFilename, "-q 80", status => {
             ...
           }
         );
       });
  })
  .then(/*happy path=*/() => {
    console.log(`Image ${file.name} has been converted.`);

    // Upload the converted image back into the bucket.
    return file.bucket.upload(newLocalFilename, { destination: file.name })
      .catch((err) => {
        console.error('Failed to upload converted image.', err);
        return Promise.reject(err);
      });
  },
  /*unhappy path=*/ (error) => { 
      console.log("oops something went wrong during uploading"); 
  })
  /*catch all rejection=*/
  .catch(error => {
       console.log("something bad happened somewhere, rollback!");
   });