title: jQuery change hash (fragment identifier) while scrolling down page
body: <p>I'm building a one pager website. Eg. every page (5 in total) is on one big page with the main menu fixed at the top. When you click on a menu link it slides you down to that pages anchor tag and the clicked menu item get a "active" CSS class.  </p>
  
  <p>What I'd like to do now is allow the user to scroll themself but still have the menu "active" item and URL hash change as they do.</p>
  
  <p>So my question basically is how do I know when the user has scrolled down to a different page so I can update the menu and URL hash (fragment identifier).</p>
  
  <p>Thanks</p>