mandatoryFields = new Array("Betreff", "Name", "Vorname", "EMail", "Text");
mailFields = new Array("EMail");
emptyFields = new Array();

Array.prototype.in_array = function(needle) {
	for(var i = 0; i < this.length; i++)
		if(this[i] === needle)
			return true;
	return false;
}

function checkForm() {
	// Initialize the array
	emptyFields = new Array();
	
	for(var i = 0; i < mandatoryFields.length; i++) {
		if(document.getElementById(mandatoryFields[i]).value == "") {
			emptyFields.push(mandatoryFields[i]);
		}
	}
	
	for(var i = 0; i < mailFields.length; i++) {
		var value = document.getElementById(mailFields[i]).value;
		
		if((value.search('@') == -1) && (!emptyFields.in_array(mailFields[i]))) {
			emptyFields.push(mailFields[i]);
		}
	}
	
	if(emptyFields.length == 0) {
		return true;
	} else {
		alert("Bitte füllen Sie noch die folgenden Felder korrekt aus:\n" + emptyFields.join(", "));
		return false;
	}
}