React useUnload hook

Handles the beforeunload window event.

• Use the useRef() hook to create a ref for the callback function, fn.
• Use the useEffect() hook and EventTarget.addEventListener() to handle the 'beforeunload' (when the user is about to close the window).
• Use EventTarget.removeEventListener() to perform cleanup after the component is unmounted.

const useUnload = fn => {
  const cb = React.useRef(fn);

  React.useEffect(() => {
    const onUnload = cb.current;
    window.addEventListener('beforeunload', onUnload);
    return () => {
      window.removeEventListener('beforeunload', onUnload);
    };
  }, [cb]);
};

const App = () => {
  useUnload(e => {
    e.preventDefault();
    const exit = confirm('Are you sure you want to leave?');
    if (exit) window.close();
  });
  return <div>Try closing the window.</div>;
};
ReactDOM.render(<App />, document.getElementById('root'));