find Date Difference using Java Script

function DateDifference()
{
var days = 0;
var difference = 0;
var startDate = new Date(document.getElementById('txtFromDate').value);
var endDate = new Date(document.getElementById('txtToDate').value);
difference = endDate - startDate;
days = Math.round(difference/(1000*60*60*24));
alert(days.toString());
}