Persisting data with localStorage

If the data is serializable, it's fairly simple.

const getLocalStorage = (key) => 
  JSON.parse(localStorage.getItem(key))

const setLocalStorage = (key) => (state) => 
  localStorage.setItem(key, JSON.stringify(state))

// usage
const atom = atom(getLocalStorage('foo') || initialState)
atom.subscribe(setLocalStorage('foo'))