function loadXMLDoc(url) {
               
    // branch for native XMLHttpRequest object
    if (window.XMLHttpRequest) {
   
        req = new XMLHttpRequest();
        //function_name is the function to process request
        req.onreadystatechange = function_name;
        req.open("GET", url, true);
        req.send(null);
       
    // branch for IE/Windows ActiveX version
    } else if (window.ActiveXObject) {
   
        req = new ActiveXObject("Microsoft.XMLHTTP");
        if (req) {

            //function_name is the function to process request       
            req.onreadystatechange = actualizarLista;
            req.open("GET", url, true);
            req.send();
        }
    }
}