function validateForm() {
	var firstname = document.getElementById("firstname").value;
	var lastname = document.getElementById("lastname").value;
	var amount = document.getElementById("amount").value;
	var email = document.getElementById("email").value;
	var anonymous = document.getElementById("anonymous").checked;
	var amountValid = false;

	// check firstname, lastname
	if (firstname == null || firstname == "") {
		alert("Vorname nicht zulässig.");
		return false;
	}

	if (lastname == null || lastname == "") {
		alert("Nachname nicht zulässig.");
		return false;
	}

	if (amount == null || amount == "" || isNaN(amount.replace(',', '.'))) {
		alert("Betrag nicht zulässig 1.");
		amountValid = false;
		return false;
	}
	else {
		if ( amount.replace(',', '.').indexOf(".") < 0 ) {
			document.getElementById("amount").value = amount + ".00";
			amountValid = true;
		}
		
		else {
			if ( amount.length - amount.replace(',', '.').indexOf(".") == 1 ) {
				document.getElementById("amount").value = amount + "00";
				amountValid = true;
			}
			
			else {
				if ( amount.length - amount.replace(',', '.').indexOf(".") == 2 ) {
					document.getElementById("amount").value = amount + "0";
					amountValid = true;
				}
				else {
					if ( amount.length - amount.replace(',', '.').indexOf(".") > 3 ) {
						alert("Betrag nicht zulässig 2.");
						return false;
					}
				}
			}
		}
	}

	if ( amountValid ) {
//		if ( document.getElementById("amount").value < document.getElementById("minAmount").value ) {
//			alert( "Der Betrag ist kleiner als der Mindestbetrag und damit nicht zulässig." );
//			return false;
//		}
	}

	// check if email is valid
	var atpos = email.indexOf("@");
	var dotpos = email.lastIndexOf(".");

	if (atpos < 1 || dotpos < atpos + 2 || dotpos + 2 >= email.length) {
		alert("Email nicht zulässig.");
		return false;
	}

	return true;
}

var oldNumber;

function checkIfNumber( field ) {
	
	var newNumber = field.value;
	newNumber = newNumber.replace(',', '.');
	
	if ( isNaN(newNumber) ) {
		field.value = oldNumber;
	} 
	
	else {
		oldNumber = newNumber.replace('.', ',');
		if ( newNumber == "" || newNumber == "undefined" ) {
			newNumber = "";
		}
	}
}