var req;
var obj;

function navigate(month, year) {
   var url = "/calendar2/calendar.php?month="+month+"&year="+year;
   if(window.XMLHttpRequest) {
           req = new XMLHttpRequest();
   } else if(window.ActiveXObject) {
           req = new ActiveXObject("Microsoft.XMLHTTP");
   }
   req.open("GET", url, true);
   req.onreadystatechange = callback_calendar;
   req.send(null);
}

function callback_calendar() {
   obj = document.getElementById("calendar");

   if((req.readyState == 4) && (req.status == 200)) {
                   response = req.responseText;
                   obj.innerHTML = response;
   } else {
       obj.innerHTML = "Kalendář akcí";
   }
}