var AJAXForms;
var idVysledku;
try {
  AJAXForms = new XMLHttpRequest();
}
catch (e) {
  try {
    AJAXForms = new ActiveXObject("Msxml2.XMLHTTP");
  }
  catch (e) {
    try {
      AJAXForms = new ActiveXObject("Microsoft.XMLHTTP");
    }
    catch (e) {
      alert("Váš prohlížeč nepodporuje AJAX!");
    }
  }
}

function kontrola(policko) {
  AJAXForms.onreadystatechange = zmenaHlaseni;
  AJAXForms.open("GET", "../registraceu/kontrolanick.php?proces=ajax&pole=" + policko.name + "&hodnota=" + policko.value, true);
  idVysledku = policko.name;
  AJAXForms.send(null);
}

function zmenaHlaseni() {
  if (AJAXForms.readyState == 4) {
    var vysledek = document.getElementById(idVysledku);
    vysledek.innerHTML = AJAXForms.responseText;
    vysledek.style.visibility = "visible";
  }
}