Сергей Мельников

function request(url, callback) {
  var req = new XMLHttpRequest();
  req.open('GET', url, true);
  req.onload = function() {
    if (req.status >= 200 && req.status < 400) {
      if (callback) callback(req.responseText);
    }
  };
  req.send();
}

request('worker.xml', function(xml) {  
  document.getElementById("IDWorker").innerHTML = xml.getElementsByTagName("IDWorker")[0].childNodes[0].nodeValue;
  document.getElementById("LastName_Worker").innerHTML = xml.getElementsByTagName("LastName_Worker")[0].childNodes[0].nodeValue;
  document.getElementById("FirstName_Worker").innerHTML = xml.getElementsByTagName("FirstName_Worker")[0].childNodes[0].nodeValue;
});