Hi, Please try following way
<script type="text/javascript">
function CompareDate()
{
var fromDate = documet.getElementById('txtFromDate').value;
var toDate = documet.getElementById('txtToDate').value;
var endDate = new Date(toDate);
var startDate = new Date(fromDate);
if(fromDate!=''&&toDate!=''&&startDate>endDate)
{
alert('end date should be greater than or equal to start date');
documet.getElementById('txtToDate').value="";
return false;
}
else if(fromDate=='')
{
alert('Please enter start date!');
return false;
}
else if(toDate=='')
{
alert('Please enter end date!');
return false;
}
}
</script>