Confirm "back" browser button click in Shiny

back_button_confirm.js

history.pushState(null, null, null);
window.addEventListener('popstate', function () {

  const endProgress = confirm('This will end your session, are you sure you want to go back?');

  if (endProgress) {
    window.onpopstate = null;
    history.back();
  } else {
    history.pushState(null, null, null);
  }

});