How to display a very long page like dzone.com?
<p>If you ever visit dzone.com you'll notice that all the posts appear on 1 page only. When we scroll that page down, older posts will be added to the end of the page (and maybe some posts at the beginning of the page but outside the view port will be removed).</p>

<p>My questions are:
- how to know if the user scrolls down/up with javascript/jQuery?
- how to know if the user is at the top of the page (they click Ctrl + Home)?</p>

<p>Thank you.</p>
