function controleer(form)
{ 
 if ((form.naam.value == '') || (form.naam.value == ' '))
 {
  alert('\Missing field: name \n');
  return false;
 }
 if ((form.email.value == '') || (form.email.value == ' '))
 {
  alert('\Missing field: email\n');
  return false;
 }
 if ((form.plaats.value == '') || (form.plaats.value == ' '))
 {
  alert('\Missing field: place\n');
  return false;
 }
 form.submit();
}