var req;
var pagina='';

function genFunction() {
  var pag = pagina;

  loadXMLDoc(pag);
}

function loadXMLDoc(url) {
  if (window.XMLHttpRequest) {
    req = new XMLHttpRequest();
    req.onreadystatechange = processReqChange;
    req.open("GET",url,true);
    req.send(null);
  }
  else if (window.ActiveXObject) {
    req = new ActiveXObject("Microsoft.XMLHTTP");
    if (req) {
      req.onreadystatechange = processReqChange;
      req.open("GET", url, true);
      req.send();
    }
  }
}

function processReqChange() {
  if (req.readyState == 4) {
    if (req.status == 200) {
      response = req.responseXML.documentElement;
      
      //codigo para ejecutar cambios en la web
      
    }
    else {
      alert("Hubo un problema obteniendo los datos XML:\n" + req.statusText);
    }
  }
}

function rellenaSelect(id,zonas,zid) {
  var zn=zonas[zid];

  var select = document.getElementById(id);
  while (select.length > 0) {
    select.remove(0);
  }
  
  var opt;
  var i;
  
  select.options[0]=new Option('Selecciona una zona',0);
  
  for (i=1;i<=zn.length;i++) {
    opt=new Option(zn[i-1][1],zn[i-1][0]);
    select.options[i]=opt;
  }
}