var peticion = false; 
try { 
      peticion = new XMLHttpRequest(); 
} catch (trymicrosoft) { 
      try { 
            peticion = new ActiveXObject("Msxml2.XMLHTTP"); 
} catch (othermicrosoft) { 
      try { 
            peticion = new ActiveXObject("Microsoft.XMLHTTP"); 
} catch (failed) { 
            peticion = false; 
} 
} 
} 
  
if (!peticion) 
      alert("ERROR AL INICIALIZAR!"); 
function cargarFragmento(fragment_url, element_id) { 
      var element = document.getElementById(element_id); 
      element.innerHTML = '<p><img src="loading.gif" /> Loading</p>'; 
      peticion.open("GET", fragment_url); 
      peticion.onreadystatechange = function() { 
      if (peticion.readyState == 4) { 
            element.innerHTML = peticion.responseText; 
} 
} 
peticion.send(null); 
}