function ajaxCreateXHR(){   
    var xhr;   
    try{   
      xhr = new XMLHttpRequest();   
    } catch(e){
      var MSXmlVerze = new Array('MSXML2.XMLHttp.6.0','MSXML2.XMLHttp.5.0','MSXML2.XMLHttp.4.0','MSXML2.XMLHttp.3.0','MSXML2.XMLHttp.2.0','Microsoft.XMLHttp');   
      for(var i = 0; i <= MSXmlVerze.length; i ++){   
        try{   
          xhr = new ActiveXObject(MSXmlVerze[i]);   
         //alert(MSXmlVerze[i]);   
          break;   
        }catch(e){   
             
        }   
      }   
    }   
    if(!xhr)   
      alert("ajaxCreateXHR - can't create!");   
    else  
      return xhr;   
}

function ajaxPostRequest(url) {    
   xhr.open("POST",url);   
   xhr.onreadystatechange = ajaxPostResponse;    
   xhr.send(null);   
}  


function ajaxPostResponse(){   
   if(xhr.readyState == 4){ //funkci provedeme, pokud je požadavek ve stavu dokončeno   
      if(xhr.status == 200){ //pokračuji, jen když je vše OK   
         //akce, co má funkce provést
         // ret = xmlhttp.responseText
      }else{   
         alert("Vámi definovaný prostředek nelze nalézt!");   
      }   
   }   
} 

function ajaxGet(url) {
  xhr.open("GET", url, false);
  xhr.send(null);
  // alert(xhr.responseText);
  return xhr.responseText; 
}

var xhr = ajaxCreateXHR();