title: Check if all dropdowns in page has a selected option
body: <p>Need to enable a button on a page only if all questions have been answered, I have 5 dropdowns for this and need to make sure user answer all of them before letting him go to next step.</p>
  
  <p>Tried to iterate through each select on each change, but can't make it work, bad JS knowledge.</p>
  
  <pre><code> arr = $('.select1, .select2, .select3, .select4, .select5')
    $('.select1, .select2, .select3, .select4, .select5').on('change', function(event) {
      $.each(arr, function(index, val) {
         /* tried here something */
      });
    });
  </code></pre>
  
  <p>I was wondering may be there is a better way to do this, something like in one line: <code>select.selected.size = 5</code>.</p>
  
  <p>Thank you for any kind of help - ideas, solutions, links, etc..</p>