title: Get filesize on 'change function' before upload using Extjs
body: <p>I want to get filesize when change function run. I try more but anything didn't work.
  How can i do that thanks</p>
  
  <pre><code>   {
          xtype: 'filefield',
          name: 'upfile[]',
          buttonConfig: {
              text: 'add'
          },
          listeners: {
                'change': function(f, value){
                      alert(f.size); // not filesize
                }
          }
      }
  </code></pre>