function displayQuickMessage(message, allowOnlyOneMessage = false) {
  const navRegion = document.querySelector('#nav-region');

  // Exit from function when window is not displayed
  if (!navRegion) return;

  // Show the message only when no other message is showing up.
  // If `allowOlyOneMessage` is `true`
  if (allowOnlyOneMessage && navRegion.querySelector('.quick-msg')) return;

  const elt = document.createElement('div');
  elt.innerHTML = message;

  navRegion.appendChild(elt);
  elt.className = 'quick-msg';
  setTimeout(() => navRegion.removeChild(elt), 5000);
}
Displays `message` for short timespan near the `nav region`.

@param {string} message
Message that you want to display

@param {boolean} allowOnlyOneMessage
Show the message only when no other quick message is showing up.