在 javascript 中实现回调

Question

我的帮助程序 js 文件中有一个函数可以在 S3 上上传文件：

module.exports.uploadToAWS = function uploadToAWS(folderName, fileName, fileData) {

  var s3 = new AWS.S3({ params: {Bucket: ‘myBucket’} });

  var keyName = folderName + "/" + fileName;

  var buffer = new Buffer(fileData.replace(/^data:image\/\w+;base64,/, ""),'base64')

  var data = {
    Key: keyName, 
    Body: buffer,
    ContentEncoding: 'base64',
    ContentType: 'image/jpeg'
  };

  s3.putObject(data, function(err, data) {
    if (err) { 
      console.log(err);
      console.log('Error uploading data: ', data); 
    } else {
      console.log('succesfully uploaded the image!');
    }
  });
}

我的消费函数是这样的：

if(images) {
  images.forEach(function(imageRecord) {
    awsHelper.uploadToAWS('assets', assetObject.id, imageRecord);
  });            
}

我想在这里引入一个回调方法，这样我就可以得到从我的辅助函数到我的调用函数的成功和失败。如何实施？需要我的消费者函数如下所示，但是辅助函数应该是什么样的？

if(images) {
  images.forEach(function(imageRecord) {
    awsHelper.uploadToAWS(
      'assets',
      assetObject.id,
      imageRecord,
      function (success, failure) {
        //handle success or failure
      });
  });
}

Answer 1

为什么不直接在 "uploadToAWS" 中添加回调，例如：

module.exports.uploadToAWS = function uploadToAWS(folderName, fileName, fileData, callback){

然后做一个简单的验证，在你上传的时候调用它（Passing the Response）completes/fails

s3.putObject(data, function(err, data){
      if (err) { 
        console.log(err);
        console.log('Error uploading data: ', data); 
        if(typeof callback === 'function') callback(err , data);
      } else {
        console.log('succesfully uploaded the image!');
        if(typeof callback === 'function') callback(err , data);
      }
    });

在此之后，您将完全按照您的建议使用它

if(images){
            images.forEach(function(imageRecord){
                awsHelper.uploadToAWS('assets', assetObject.id, imageRecord, function (err , data) {
                    //handle success or failure    
                });
            });            
        }

Answer 2

您需要将回调函数作为辅助函数的参数传递。

试试这个：

module.exports.uploadToAWS = function uploadToAWS(folderName, fileName, fileData, callback){

    var s3 = new AWS.S3({ params: {Bucket: ‘myBucket’} });

    var keyName = folderName + "/" + fileName;

    var buffer = new Buffer(fileData.replace(/^data:image\/\w+;base64,/, ""),'base64')

    var data = {
        Key: keyName, 
        Body: buffer,
        ContentEncoding: 'base64',
        ContentType: 'image/jpeg'
    };

    s3.putObject(data, function(err, data){
       if (err) { 
         callback(err);
       } else {
         callback(null, data);
       }
    });
}

Answer 3

因此，通过以 Promise 样式重写，您可以：

module.exports.uploadToAWSAsync = 
    function uploadToAWSAsync(folderName, fileName, fileData){
        return new Promise(function(resolve, reject){
            var s3 = new AWS.S3({ params: {Bucket: ‘myBucket’} });

            var keyName = folderName + "/" + fileName;

            var buffer = new Buffer(fileData.replace(/^data:image\/\w+;base64,/, ""),
                                    'base64')

            var data = {
                    Key: keyName, 
                    Body: buffer,
                    ContentEncoding: 'base64',
                    ContentType: 'image/jpeg'
                };

            s3.putObject(data, function(err, data){
                  if (err) { 
                    console.log(err);
                    console.log('Error uploading data: ', data); 
                    reject(err);
                  } else {
                    console.log('succesfully uploaded the image!');
                    resolve();
                  }
                });
        });
    }

您可以按如下方式重写您的消费者代码：

//fire them all off in one go
var promises = images.map(function(imageRecord){
    return awsHelper.uploadToAWSAsync('assets', assetObject.id, imageRecord);
}); 
Promise.all(promises).then(function(){
    //success, everything uploaded
}).catch(function(err){
    //something went wrong
});

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