// only load the map viewer when it's visible (and javascript is enabled)
document.addEventListener('DOMContentLoaded', (event) => {
  const setMap = () => { document.querySelector('#map').src = 'map/' }
  const details = document.querySelector('details:last-child')

  // if <details> is not supported (looking at you, Edge), the frame will be
  // visible by default, so just set the target immediately
  if ('open' in details)
    details.addEventListener('toggle', setMap, { once: true })
  else
    setMap()
})