function checkcontactform()
	{
	var emailfilter=/^\w+[\+\.\w-]*@([\w-]+\.)*\w+[\w-]*\.([a-z]{2,4}|\d+)$/i;
	
		if(document.contactform.firstname.value=='') {
			alert('Gelieve uw voornaam in te vullen');
			document.contactform.firstname.focus();
		}
		else if(document.contactform.lastname.value=='') {
			alert('Gelieve uw familynaam in te vullen');
			document.contactform.lastname.focus();
		}
		else if(document.contactform.email.value=='') {
			alert('Gelieve uw emailadres in te vullen');
			document.contactform.email.focus();
		}
		else if(document.contactform.subject.value=='') {
			alert('Gelieve een onderwerp in te vullen');
			document.contactform.subject.focus();
		}
		else if(document.contactform.message.value=='')	{
			alert('Gelieve een mededeling in te vullen');
			document.contactform.message.focus();
		}
		else {
			var returnval=emailfilter.test(document.contactform.email.value);
			if (returnval==false) {
				alert('Gelieve een geldig emailadres in te vullen.');
				document.contactform.email.focus();
			} else {
				document.contactform.submit();
			}
		}
	}