function checkForm() {
naam = document.getElementById("naam").value;
telefoon = document.getElementById("telefoon").value;
  
  if (naam == "") {
  hideAllErrors();
document.getElementById("naamError").style.display = "inline";
document.getElementById("naam").select();
document.getElementById("naam").focus();
  return false;
  } else if (telefoon == "") {
hideAllErrors();
document.getElementById("telefoonError").style.display = "inline";
document.getElementById("telefoon").select();
document.getElementById("telefoon").focus();
  return false;
   }
  return true;
  }
 
  function hideAllErrors() {
document.getElementById("naamError").style.display = "none"
document.getElementById("telefoonError").style.display = "none"
  }