如何在ajax / js中等待线程，直到用户在文件上传期间选择文件？

Question

以下是代码，它可以帮助您更好地理解问题。 HTML代码： -

{{#each uploadsData as |row|}}
  <div {{action 'upload' row uploadsData}} class="mdl-cell mdl-cell--12-col mdl-grid kyc-uploads__form_uploads_documents-grid">
    <div class="mdl-cell--2-col mdl-cell--hide-phone kyc-uploads__form_uploads_documents-grid_icon">
      {{inline-svg row.svg}}
    </div>
    <div class="mdl-cell--10-col  mdl-cell--12-col-phone kyc-uploads__form_uploads_documents-grid__text">
      <span class="mdl-cell--hide-desktop" style="padding: 5%;">{{inline-svg row.svg}}</span>
      <span class="kyc-uploads__form_uploads_documents-grid__text_title">{{row.heading}}</span>
      <span class="kyc-uploads__form_uploads_documents-grid__text_subText">
        {{if (eq row.optional true) "(Optional)" ""}}
      </span>
      <span class="kyc-uploads__form_uploads_documents-grid__text_select {{if (eq row.isSubmitted true) "kyc-uploads__form_uploads_documents-grid__text_select_completed" ""}}">
        <i class="material-icons">done</i>
      </span>
    </div>
  </div>
  <input type="file" style="visibility: hidden; display: none;" id="{{row.key}}" name="{{row.key}}" value="{{inputFile}}" />
{{/each}}

JS代码： -

upload(row, uploadsData) { 
    var el =$('#'+row.key);
    el.click();
    var file = el[0].files[0];
    console.log(file);
    if(file != null){
        //do something...
    }); 
    this.controller.set('isCompleted', completionStatus);
}

当用户点击el.click()进行文件上传时，会打开一个对话框来选择文件。 现在这里是一个线程自动退出循环的技巧，因为文件尚未被选中而另一个正在要求用户选择一个文件。那么你有什么想法我怎么能等到文件是否为空，直到用户选择文件??