var addEvent;
if (document.addEventListener) {
  addEvent = function(element, type, handler) {
    element.addEventListener(type, handler, false);
  };
} else if (document.attachEvent) {
  addEvent = function(element, type, handler) {
    element.attachEvent("on" + type, handler);
  };
} else {
  addEvent = new Function; // not supported
}