title: Abort upload with UIkits Upload Component?
body: <p>The title says it all. How can I abort the upload with UIKits Upload Component?</p>
  <p>I'm trying to abort the upload in the <code>beforeAll</code> callback but I can't seem to get it to work.</p>
  <pre><code>UIkit.upload('.js-upload', {
      url: '',
      multiple: false,
      mime: 'audio/*',
      allow: '*.mp3',
  
      beforeAll: function () {
        return false; // &lt;--- Why does it not return/abort?
        });
      }
   });
  
  </code></pre>