code: function doFocusExit(el, fromElement, toElement) {
      el.dispatchEvent(new CustomEvent('focusExit', {
          detail: { fromElement: fromElement, toElement: toElement },
          bubbles: false // mirror the native mouseleave event
      }));
  }
docs: requires CustomEvent polyfill for IE9+ https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent/CustomEvent