How to capture scroll event?

The correct way to implement it is:

 <div id="container" onScroll="handleOnScroll();">

<script>
function handleOnScroll() {
        alert("scroll");
    };
</script>

EDIT: Since you originally tagged your question with jquery...

---

To capture the scroll event using jQuery...

HTML:

<div id="container">
    CONTENT
</div> 

jQuery:

$(document).ready(function() {

    $('#container').scroll(function() {
        alert('scroll');
        // presumably your infinite scrolling code here
    });

});

See: http://api.jquery.com/scroll/