function creaAjax(){
   if (window.XMLHttpRequest) return new XMLHttpRequest();
   else if (new ActiveXObject('Msxml2.XMLHTTP')) return new ActiveXObject('Msxml2.XMLHTTP');
   else if (new ActiveXObject('Microsoft.XMLHTTP')) return new ActiveXObject('Microsoft.XMLHTTP');
}

function libreriaAJAX (_VARS,_URL)
{
   var ajax=creaAjax();
   this.layer = '';
	 this.vars=_VARS;
	 this.url=_URL;
	 //var action_=null;
	 var action_ = function(text){
			document.getElementById(layer_).innerHTML=text;
	 }

	 this.setdefault=function(){
		action_ = function(text){alert(this.layer_);} 
	}
	 
/*Creamos y ejecutamos la instancia si el metodo elegido es POST*/
   this.setaction_=function(func){
	 action_=func;
	}

	this.abort = function(){ajax.abort();}

		this.ejecution = function (){
		ajax.open ('POST', this.url, true);
    ajax.onreadystatechange = function() {
         if (ajax.readyState==1) {
                 //this.capaContenedora.innerHTML="";
         }
         else if (ajax.readyState==4){
            try{
						if(ajax.status==200)
            {
             // alert('completado');
							action_(ajax.responseText); 
            }
						else
						{
							ObjGen.deleteBox();
						}
						}
						catch(err)
						{ObjGen.deleteBox();}

        }
    }
    ajax.setRequestHeader('Content-Type','application/x-www-form-urlencoded');
    ajax.send(this.vars);
		}

}