function checkEmailAdres(email) {

   var reg = /^([A-Za-z0-9_\-\.])+\@([A-Za-z0-9_\-\.])+\.([A-Za-z]{2,4})$/;

   return reg.test(email)
}

function checkPostcode(postcode) {

  postcode = postcode.replace(/(^\s*)|(\s*$)/g, "");

  return postcode.match(/^[1-9][0-9]{3}[\s][A-Z]{2}$/i);
}

function checkForm() {

    ok = true;

    if(document.forms[0].naam.value == "") {
        document.getElementById("naam").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("naam").style.display = 'none';
    }

    if(document.forms[0].organisatie.value == "") {
        document.getElementById("organisatie").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("organisatie").style.display = 'none';
    }

    if(document.forms[0].functie.value == "") {
        document.getElementById("functie").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("functie").style.display = 'none';
    }

    if(document.forms[0].email.value == "" || !checkEmailAdres(document.forms[0].email.value)) {
        document.getElementById("email").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("email").style.display = 'none';
    }

    if(document.forms[0].postcode.value != "" && !checkPostcode(document.forms[0].postcode.value)) {
        document.getElementById("postcode").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("postcode").style.display = 'none';
    }

    if(document.forms[0].omschrijving.value == "") {
        document.getElementById("omschrijving").style.display = 'inline';
        ok = false;
    }
    else {
        document.getElementById("omschrijving").style.display = 'none';
    }

    return ok;
}