Javascript，使用Promises上传Array.reduce中的几个文件，怎么样？

从Javascript, spliced FileReader for large files with Promises, how?演变，它向我展示了Promise如何也可以解析一个函数，现在我仍然坚持使用相同但在Array.reduce函数内部 .

目标是我想在一个数组中上传一个文件（已经存在），其中每个数组项（文件）按顺序上传（即通过promises控制） .

然后，我明白答案是以某种方式在http://www.html5rocks.com/en/tutorials/es6/promises/?redirect_from_locale=es，但我无法理解如何将其应用到这里 . 我的数组不是promises数组，是一个文件数组 . 好吧，整件事情仍然让我感到困惑 .

这是我的代码，如果我能看到 ein console.log消息，它将起作用：

return myArray.reduce(function(previous, current) {
    var BYTES_PER_CHUNK = 100000;
    var start = 0;
    var temp_end = start + BYTES_PER_CHUNK;
    var end = parseInt(current.size);
    if (temp_end > end) temp_end = end;
    var content = ''; // to be filled by the content of the file
    var uploading_file = current;
    Promise.resolve().then(function() {
        return upload();
    })
    .then(function(content){
        // do stuff with the content
        Promise.resolve();
    });
},0)  // I add the 0 in case myArray has only 1 item
//},Promise.resolve()) goes here?

.then(function(){
    console.log('ein') // this I never see
});

function upload() {
  if (start < end) {
    return new Promise(function(resolve){
      var chunk = uploading_file.slice(start, temp_end);
      var reader = new FileReader();
      reader.readAsArrayBuffer(chunk);
      reader.onload = function(e) {
        if (e.target.readyState == 2) {
          content += new TextDecoder("utf-8").decode(e.target.result);
          start = temp_end;
          temp_end = start + BYTES_PER_CHUNK;
          if (temp_end > end) temp_end = end;
          resolve(upload());
        }
      }
    });
  } else {
    uploading_file = null;
    return Promise.resolve(content);
  }
}

经过几次评论后

• 更新了，现在似乎已经有效了......还不确定

var uploaded_file，start，temp_end，end，content; var BYTES_PER_CHUNK = 100000;

myArray.reduce（function（previous，current）{return previous .then（function（）{BYTES_PER_CHUNK = 100000; start = 0; temp_end = start BYTES_PER_CHUNK; end = parseInt（current.size）; if（temp_end> end）temp_end = end; content =''; uploaded_file = current;

upload()
.then(function(content){
    // do stuff with "content"
    console.log('here')
    return Promise.resolve();
});

}）; }，Promise.resolve（）） . then（function（）{console.log（'ein'）;}）;

function upload（）{if（start <end）{return new Promise（function（resolve）{var chunk = uploaded_file.slice（start，temp_end）; var reader = new FileReader（）; reader.readAsArrayBuffer（chunk）; reader . onload = function（e）{if（e.target.readyState == 2）{content = new TextDecoder（“utf-8”） . decode（e.target.result）; start = temp_end; temp_end = start BYTES_PER_CHUNK; if （temp_end> end）temp_end = end; resolve（upload（））;}}}）; } else {uploaded_file = null; return Promise.resolve（content）; }}

• 改进了代码，似乎工作，也许更容易阅读？

var start, temp_end, end;
    var BYTES_PER_CHUNK = 100000;

    myArray.reduce(function(previous, current) {
        return previous
        .then(function() {
            start = 0;
            temp_end = start + BYTES_PER_CHUNK;
            end = parseInt(current.size);
            if (temp_end > end) temp_end = end;
            current.data = '';

            return upload(current)
            .then(function(){
                // do other stuff
                return Promise.resolve();
            });
        });
    },Promise.resolve())
    .then(function(){
      // do other stuff
    });

    function upload(current) {
        if (start < end) {
            return new Promise(function(resolve){
                var chunk = current.slice(start, temp_end);
                var reader = new FileReader();
                reader.readAsText(chunk);
                reader.onload = function(e) {
                    if (e.target.readyState == 2) {
                        current.data += e.target.result;
                        start = temp_end;
                        temp_end = start + BYTES_PER_CHUNK;
                        if (temp_end > end) temp_end = end;
                        resolve(upload(current));
                    }
                }
            });
        } else {
            return Promise.resolve();
        }
    }