// date.js required

function checkdates(myform) {

  var date1 = myform.startdate.value;
  var date2 = myform.enddate.value;
  
  if ( !isDate(date1,"MM/dd/yyyy") || !isDate(date2,"MM/dd/yyyy") ) {
    alert("ERROR: invalid date(s)!");
    return false;
  }
  
  var dt1 = getDateFromFormat(date1,"MM/dd/yyyy");
  var dt2 = getDateFromFormat(date2,"MM/dd/yyyy");

  var diff = dt2-dt1;
  var days = diff/1000/60/60/24;
    
  if (days<0) {
	alert("ERROR: not a valid interval!");
	return false;
  }

  if (days>30) {
	alert("ERROR: the length of the date interval cannot exceed 30 days!");
	return false;
  }
  
  return true;
}