PROSAGA码农传奇-html/HTML5-以编程方式更改输入类型文件的值？

<div class =“post-text”itemprop =“text”>
  
    我认为问题是你期望的那样
  
   <pre>
 <code>
 reader.onload = () => {
 photo = this.createPhotoThumb({
 url : reader.result,
 name: file.name,
 size: file.size
 });
 if (this.validatePhoto(file)) {
 this.validFiles.items.add(file);
 };
};

</code>
 </pre>
  
    在分配有效文件之前执行get
     <code>
 this.output.files
 </code>
    。
  
  
    但
     <code>
 reader.onload
 </code>
     异步执行，以便将有效文件分配给
     <code>
 this.output.files
 </code>
     在将有效文件添加到有效文件数组之前执行。
  
  
    你必须实现一些等待完整性的逻辑
     <code>
 onload
 </code>
     读者的处理程序。
  
  
    这将是一个可能的解决方案：
  
   <pre>
 <code>
 class PhotoPicker
{
 constructor(element)
 {
 this.element = element;

// Creating needed HTML Markup
        this.createMarkUp();

// FileList of valid data.
        this.validFiles = new DataTransfer();

// Initialise Picker.
        this.input.onchange = () => {
            this.updateOutput()
                .then(() => {
                    this.output.files = this.validFiles.files;
                });
        }
    }

updateOutput()
    {
        const files = Array.from(this.input.files);
        const fileLoaderPromises = [];
        files.forEach((file) => {
            const promise = new Promise((resolve) => {
                let reader = new FileReader();
                reader.readAsDataURL(file);
                reader.onload = () => {
                    photo = this.createPhotoThumb({
                        url : reader.result,
                        name: file.name,
                        size: file.size
                    });
                    if (this.validatePhoto(file)) {
                        this.validFiles.items.add(file);
                    };
                    // Mark the file loader as "done"
                    resolve();
                };
            })

// Add the promise to the list of file loader promises
            fileLoaderPromises.push(promise);
        });

// Return a promise which resolves as soon as all file loader promises are done
        return Promise.all(fileLoaderPromises);
    }

// ...
}

</code>
 </pre>
</DIV>