Reservair/src/components/admin.js

function create_notice(id, type, mesg) {
  let container = document.createElement('div');
  container.id = id;
  container.classList.add('notice', `notice-${type}`, 'settings-error', 'is-dismissible');
  container.innerHTML = `<p><strong>${mesg}</strong></p>`;
  return container;
}

export function show_notice(target, type, mesg) {
  target.querySelectorAll('.notice').forEach(x => x.remove());
  const notice = create_notice('test', type, mesg);
  target.prepend(notice);
}