Question

我正在编写一个脚本，使我能够创建一个上传文件的对象，并且应该有方法来获取属性，例如上传文件的总大小，让我告诉你：

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分配，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，我得到了未定义的错误，例如cannot read property push of undefined.

我真的希望你能帮助我，非常感谢你！

Answer 1

对于每个寻求快速解决方案的人来说，这里都是一个易于理解的解决方案：

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);
}

这是我发现的最基本的例子。我希望它可以帮助你。

Javascript返回变量值形成一个对象

1 个答案: