test03.html

<meta charset="utf-8">

<button id="btn">Pozdrav</button>

<div id="result" style="border: solid 2px red;"></div>

<script>

window.onload = function() {
  var button = document.getElementById("btn");
  btn.onclick = function() {
    xhr = new XMLHttpRequest();
    xhr.onreadystatechange = function() {
      console.log("State: " + xhr.readyState);
      if (xhr.readyState === XMLHttpRequest.DONE) {
        if (xhr.status === 200) {
          var osoba = xhr.responseXML;
          var result = document.getElementById("result");
          result.innerHTML = "Jméno je " + osoba.getElementsByTagName("jmeno").item(0).textContent
                             + " a věk je " + osoba.getElementsByTagName("vek").item(0).textContent;
        } else {
          alert("Server error: " + xhr.status);
        }
      }
    }
    xhr.open("GET", "http://localhost:8000/data.xml");
    xhr.send();
  };
}

</script>