data fetching while scrolling just like facebook

<script language="javascript" src="http://www.infoonnet.com/js/jquery.js"></script>
<script>
$(document).scroll(function(){
    if ($(window).scrollTop() + $(window).height() == $(document).height())
{
       document.getElementById("a").innerHTML+='<div style="height:100%; border:1px solid red" id="a">pag1 1</div>';
    }
});
</script>



<div style="height:100%; border:1px solid red" id="a">
pag1 1
</div>
<div style="height:100%; border:1px solid red" id="b">
pag1 1
</div>