function validateCardLogin(thisForm, digits_required) {

   if (thisForm.cardnumber.value.length < digits_required ) { 
   		alert('Please enter the first '+digits_required+' digits of your card'); 
		thisForm.cardnumber.focus();
		return false; 
	}
   else if (!isInt(thisForm.cardnumber.value)) { 
   		alert('Please enter digits only'); 
		thisForm.cardnumber.focus();
		return false; 
	}
   return true;  
}
  
function isInt (str) {
	var i = parseInt (str);
	if (isNaN (i)) { return false; }
	i = i . toString ();
	if (i != str) { return false; }
	return true;
}