dynamic textfield var score not working in facebook post

dynamic textfield var score not working in facebook post . Rather it showing "OBJECT TEXT FEILD"

import flash.events.Event;

btnFB.addEventListener(MouseEvent.CLICK, gotoFB);

function gotoFB(e:Event)

{

  var url:String = "https://www.facebook.com/dialog/feed?" +

  "%20app_id=1487500124800564%20&display=popup" +

  "&caption=I%20just%20scored%20" + score +

  "&link=graphicscoder.org" +

  "&redirect_uri=https://www.facebook.com/";

  navigateToURL(new URLRequest(url), "_blank");

}