Javascript 从对象中返回变量值

Question

我正在编写一个脚本，该脚本使我能够创建一个上传文件的对象，并且该对象应该具有获取属性(例如上传文件的总大小)的方法，让我向您展示:

function FileUploader = function (to){
    let html = "some html with the form...";
    to.append(html);
    let input = 'someSelector...';
    let allSizes = [];
    let allSrcs = [];
    let totalSize = 0;
    input.on('change', function (){
        //some validation
        let data = new FormData();
        //for loop to append the input files
        let request = createRequest(); //createRequest returns a request...
        request.addEventListener("load", function (evt){
             for( let i = 0; i<input.files.length; i++){
                 totalSize+= input.files[i].size;
                 allSizes.push(input.files[i].size);
             }
             let response = JSON.parse(e.currentTarget.responseText);
             for(let i = 0; i<response.length; i++){
                allSrcs.push(response[i]);
             }
             alert("Ok");
        );
        //other request handlers
        request.open("POST", 'someLocalPath');
        request.send(data);
    });
}

Uploader.prototype.getSrcs= function (){
    //the problem comes here, I can't pass the value of any variable in the object
}

我尝试将 let 变量转换为 this 赋值，如下所示:

 function FileUploader = function (to){
    let html = "some html with the form...";
    to.append(html);
    let input = 'someSelector...';
    this.allSizes = [];
    this.allSrcs = [];
    this.totalSize = 0;
    input.on('change', function (){
        //some validation
        let request = createRequest(); //createRequest returns a request...
        request.addEventListener("load", function (evt){
             for( let i = 0; i<input.files.length; i++){
                 this.totalSize+= input.files[i].size;
                 this.allSizes.push(input.files[i].size);
             }
             let response = JSON.parse(e.currentTarget.responseText);
             for(let i = 0; i<response.length; i++){
                this.allSrcs.push(response[i]);
             }
             alert("Ok");
        );
    });
}

在最后一种情况下，我收到未定义的错误，例如无法读取未定义的属性推送。

真心希望您能帮助我，非常感谢!

Answer 1

对于寻求易于理解的快速解决方案的每个人来说，这里有一个解决方案:

function Person() {
  var that = this;
  that.age = 0;

  setInterval(function growUp() {
    // The callback refers to the `that` variable of which
    // the value is the expected object.
    that.age++;
  }, 1000);
}

这是我找到的最基本的例子。希望对您有帮助。