//contactform validatie
function addFieldToCheck() {
  var elem=document.contactform.emailadres.value;
  var emailfilter  = /^([a-zA-Z0-9_\.\-])+\@(([a-zA-Z0-9\-])+\.)+([a-zA-Z0-9]{2,4})+$/;
	if(!elem && elem!="") {
    alert ("U dient een emailadres op te geven\nplease provide an emailaddress");
    return false;
  }
  if (!emailfilter.test(elem)) {
    alert("Het emailadres is niet geldig\nThe provided emailaddress is not valid");
    return false;
  }
  else {
   document.contactform.submit();
   return true;
  }
}