// Create xmlHttp object for AJAX calls
var xmlHttp;
if (window.XMLHttpRequest){
  xmlHttp = new XMLHttpRequest();
} else if (window.ActiveXObject){
  xmlHttp = new ActiveXObject("Msxml2.XMLHTTP");
}

// This function performs AJAX calls.
function AJAX(url,data){
  xmlHttp.open("POST",url,false);
  xmlHttp.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
  xmlHttp.setRequestHeader("Content-length", data.length);
  xmlHttp.setRequestHeader("Connection", "close");
  xmlHttp.send(data);
  var server_response = xmlHttp.responseText;
  return server_response;
}

// This function handles AJAX errors gracefully.
function ajaxError(e){
  return false;
}

// Main function for retrieving data using AJAX functions above
function getData(parameters){
  var url = "ajax";
  var data = parameters + "&nocache=" + Math.random();
  try{
    var response = AJAX(url,data);
    if(response != ''){
      // Do something with the returned data
      return response;
    } else {
      // Do whatever is done if no data was returned
      return false;
    }
    
  } catch(e) {
    return ajaxError(e);
  }
}

// Refreshes the updates calendar with a specified month / year combination.
function calendarSwitch(month,year){
  // Get the calendar
  var newCalendar = getData('mode=calendar&month=' + month + '&year=' + year);
  if(newCalendar != false){
    document.getElementById('calendar').innerHTML = newCalendar;
  }
}