title: Get element classes with shinyjs
body: <p>I would like to print/output the classes of a div in shiny.
  The documentation doesn't seem to have anything for shinyjs, is it because it is very simple and I overlooked it?</p>
  <p>I'm imagining something along the lines of:</p>
  <pre><code>div('mydiv1', class=&quot;box greatDiv keepTop&quot;) 
  </code></pre>
  <pre><code>getClasses(id='mydiv1')
  &gt; box greatDiv keepTop
  </code></pre>