var request;

window.onload = function() {
  try {
    request = new XMLHttpRequest();
  } catch (poikkeus) {
    console.log(poikkeus);
  }
  request.onreadystatechange = lisaa_xml;
  request.open("POST", "testi2.php", true);
  request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
  request.send(null);
  document.getElementById('kasvis').addEventListener('click', vaihda_lista, false);
}

function vaihda_lista() {
  var checkbox = document.getElementById('kasvis');
  if (checkbox.checked) {
    request.open("POST", "testi2.php", true);
    request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    request.send("kasvis=on");
  } else {
    request.open("POST", "testi2.php", true);
    request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    request.send("");  
  }
}

function lisaa_teksti() {
  if (request.readyState == 4 && request.status == 200) {
    var p = document.getElementById('kappale');
    p.textContent = request.responseText;
  }
}

function lisaa_xml() {
  if (request.readyState == 4 && request.status == 200) {
    var select = document.getElementById('valitse');
    var uusiselect = document.importNode(request.responseXML.documentElement, true);
    select.parentNode.replaceChild(uusiselect, select);
  }
}