Q217 How can I calculate the difference between two dates?

<script language="JavaScript"><!--
function timeDifference(laterdate,earlierdate) {
    var difference = laterdate.getTime() - earlierdate.getTime();

    var daysDifference = Math.floor(difference/1000/60/60/24);
    difference -= daysDifference*1000*60*60*24
    var hoursDifference = Math.floor(difference/1000/60/60);
    difference -= hoursDifference*1000*60*60
    var minutesDifference = Math.floor(difference/1000/60);
    difference -= minutesDifference*1000*60
    var secondsDifference = Math.floor(difference/1000);

    document.write('difference = ' + daysDifference + ' day/s ' + hoursDifference + ' hour/s ' + minutesDifference + ' minute/s ' + secondsDifference + ' second/s ');
}

var laterdate = new Date(2000,0,1);     // 1st January 2000
var earlierdate = new Date(1998,2,13);  // 13th March 1998

timeDifference(laterdate,earlierdate);
//--></script>