title: set progress bar value from variable
body: <p>I have a variable which updates based on percent file downloaded. How can I get this variable to update a progress bar?</p>
  
  <pre><code>var percent = (len / res.headers['content-length']) * 100;
  </code></pre>
  
  <p>I have tried this to no avail:</p>
  
  <pre><code>&lt;progress class="progress"&gt;&lt;/progress&gt;
  
  $('.progress').val = percent;
  </code></pre>