title: How often does xhr.upload.onProgress fire?
body: <p>I am subscribing to the onProgress event when uploading a file via XHR.  My progress bar is animated (via jQuery) to provide a better visual aesthetic.</p>
  
  <p>onProgress seems to fire very rapidly, so I wondered how often it actually gets fired so that I can somehow devise a process whereby I can throttle responses to this so that I can have one continuously animated progress bar</p>