// variables y constantes
var READY_STATE_UNINITIALIZED=0;
var READY_STATE_LOADING=1;
var READY_STATE_LOADED=2;
var READY_STATE_INTERACTIVE=3;
var READY_STATE_COMPLETE=4;
var req;
var valor_load;


// crea el objeto de conexi?n
function getXMLHTTPRequest() {
  var xRequest=null;
  if (window.XMLHttpRequest) {
    xRequest=new XMLHttpRequest();	// mozilla - safari
  }else if (typeof ActiveXObject != "undefined"){
    xRequest=new ActiveXObject
     ("Microsoft.XMLHTTP");	// ie
  }
  return xRequest;
}


// env?a una petici?n
function sendRequest(url,params,HttpMethod){
  if (!HttpMethod){
    HttpMethod="GET";
  }
  req=getXMLHTTPRequest();
  if (req){
    req.onreadystatechange=onReadyStateChange;
    req.open(HttpMethod,url,true);
    req.setRequestHeader
         ("Content-Type", "application/x-www-form-urlencoded");
    req.send(params);
  }
}

// seg?n el estado se realiza algo
function onReadyStateChange(){
  var ready=req.readyState;
  var data=null;
  if (ready==READY_STATE_COMPLETE){
    data=req.responseText;
  }else{
    data="cargando...["+ready+"]";
  }
  valor_load=data;
}