var httpReq;
var targetObj;
var msgsObj;
var oTdName;
var oTdValType;

function createRequestObject() {
   var ro;

   if (window.XMLHttpRequest) {
      ro = new XMLHttpRequest();
   } else {
      if (window.ActiveXObject) {
         ro = new ActiveXObject("Microsoft.XMLHTTP");
      }
   }
   return ro;
}

function getData(tObj, msgObj, chsdVl) {
   targetObj      = document.getElementById(tObj);
   msgsObj        = document.getElementById(msgObj);

   if((chsdVl != '') || (chsdVl == -1)) {
      msgsObj.style.display = "block";
      httpReq = createRequestObject();
      var aParams = new Array();
      var sParam = encodeURIComponent("chsdVl");
      sParam += "=";
      sParam += encodeURIComponent(chsdVl);
      aParams.push(sParam);

      sBody = aParams.join("&");
      url = "get_cities.php";
      httpReq.open("POST", url, true);
      httpReq.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
      httpReq.onreadystatechange = handleResponse;
      httpReq.send(sBody);
   }
}

function checkReadyState() {
   if(httpReq.readyState < 4) {
      msgsObj.innerHTML = "<strong>зареждане...</strong>";
   } else if(httpReq.readyState == 4) {
      msgsObj.style.display = "none";
      return (httpReq.status == 200);
   }
}

function handleResponse() {
   if(checkReadyState()) {
      if(httpReq.responseText) {
         targetObj.innerHTML = httpReq.responseText;
      } else
         targetObj.innerHTML = '';
   }
}