function addEvent(elm, evType, fn, useCapture){
  if(elm.addEventListener){
    elm.addEventListener(evType, fn, useCapture);
    return true;
  }
  else if (elm.attachEvent){
    var r = elm.attachEvent('on' + evType, fn);
    return r;
  }
  else{
    elm['on' + evType] = fn;
  }
}