javascript - Nodejs while 循环未按预期工作 - 变得无限

Question

我创建了一个中间件，用于在创建新的个人资料图片/封面照片上传时删除 aws 文件。

//if previous awsKeys detected in req.body / images are detected : delete them.
exports.multipleDelete = function(req, res, next){
  var body = req.body;
  var awsKeyTrash = body.existingKeys;
  if(awsKeyTrash !== undefined){
    var j = 0;
    while (j < awsKeyTrash.length){
      console.log('j ', j)
      var key = awsKeyTrash[j];
      s3.deleteObject({
        Bucket: aws.bucket,
        Key: key
      }, function(err,data){
        if (err){
           console.log('delete err', err);
            j++;
          };
        console.log('deleted')
        res.send('deleted');
        j++;
      });
    }
    next();
  }
  else{
    next();
  }
}

console.log结果:

j  0
j  0
j  0
j  0
j  0
j  0
j  0
j  0
j  0
j  0 .....

使用上面的代码，我得到了一个无限循环。但是，如果我使用 for 循环，它就可以正常工作..

Answer 1

s3.deleteObject 是一个异步调用，您在调用仍在进行时立即迭代 while 循环!

您应该考虑使用异步框架，例如 async 。代码如下所示:

//if previous awsKeys detected in req.body / images are detected : delete them.
exports.multipleDelete = function(req, res, next){
  var body = req.body;
  var awsKeyTrash = body.existingKeys;
  if(awsKeyTrash !== undefined){
    var j = 0;
    async.whilst(
      function(){ return j < awsKeyTrash.length; }
      function(){
        console.log('j ', j)
        var key = awsKeyTrash[j];
        s3.deleteObject({
          Bucket: aws.bucket,
          Key: key
        }, function(err,data){
          if (err){
             console.log('delete err', err);
              j++;
          };
          console.log('deleted')
          res.send('deleted');
          j++;
        });
      },
      function(err){
        //while loop is finished!
        next();
    });
  }
  else{
    next();
  }
}