title: why enter and exit event not fire in jquery?
body: <p>I am using <code>scroll</code> plugin from <a href="https://github.com/thesmart/jquery-scrollspy" rel="nofollow noreferrer">github</a>
  my <strong>enter and exit</strong> event not fire</p>
  
  <p>here is my code , check link <a href="https://plnkr.co/edit/sKuOTlvZM3dCOwXfWOeR?p=preview" rel="nofollow noreferrer">plnkr</a></p>
  
  <pre><code>$(function(){
      $('.t').on('scrollSpy:enter', function() {
          console.log('enter:', $(this).attr('id'));
      });
  
      $('.t').on('scrollSpy:exit', function() {
          console.log('exit:', $(this).attr('id'));
      });
  
      $('#container .t').scrollSpy();
  
  })
  </code></pre>