ok, so i've definitely done custom hooks with a useState before

click_away_effect.js

function clickAwayListener (elementId, callback) {
  return event => {
    const outsideClick = !document.getElementById(elementId).contains(event.target)
    if (outsideClick) {
      callback()
    }
  }
}

export function useClickAway (elementId, callback) {
  const listener = clickAwayListener(elementId, callback)

  useEffect(() => {
    document.addEventListener('click', listener)
    return () => document.removeEventListener('click', listener)
  }, [])
}