function objetoAjax(url) {
var ajaxRequest=false;
  // objecto nativo
   try{
      // Opera 8.0+, Firefox, Safari
      ajaxRequest = new XMLHttpRequest();
   } catch (e){
      // Internet Explorer Browsers
      try{
         ajaxRequest = new ActiveXObject("Msxml2.XMLHTTP");
      } catch (e) {
         try{
            ajaxRequest = new ActiveXObject("Microsoft.XMLHTTP");
         } catch (e){
            // Something went wrong
            alert("Your browser broke!");
            return false;
         }
      }
   }
   return ajaxRequest;
}
