var httpRequest;
var lastControlID;
var processOutput;
  
function invalidateControl(controlID, url, parameters){  
  lastControlID = controlID;    
  processOutput = true;                
  createRequest(url, parameters, true);
}

function createRequest(url, parameters, output){
  document.getElementById('u3control'+lastControlID).innerHTML = 'Načítání...';
  processOutput = output;      
  if (window.ActiveXObject){
    httpRequest = new ActiveXObject("Microsoft.XMLHTTP");
  } else {
    httpRequest = new XMLHttpRequest();
  }
  
  httpRequest.open('POST', url, true);
  if(parameters != null){      
    httpRequest.setRequestHeader("Content-type", "application/x-www-form-urlencoded");
    httpRequest.setRequestHeader("Content-length", parameters.length);
    httpRequest.setRequestHeader("Connection", "close");
  } else {
    parameters = '';
  }                    
  
  httpRequest.onreadystatechange = function () { processRequest(); } ;
  httpRequest.send(parameters);
}

function processRequest(){
  if (httpRequest.readyState == 4){
    if(httpRequest.status == 200){
      if(processOutput) document.getElementById('u3control'+lastControlID).innerHTML = httpRequest.responseText;                                            
    } else alert('prob');
  }
}