@dzcpy I think if we use two atoms, the history can be implemented. No need for onMount in this case.

[IanDuncanson]

@dzcpy I think if we use two atoms, the history can be implemented. No need for onMount in this case.
The good way to think at first is how you would do it with useState. Then, it's straightforward to migrate to atom and useAtom. I can help on it.
Would you open a new discussion / issue?

Originally posted by @dai-shi in #211 (comment)

[IanDuncanson]

@dai-shi - I am interested in how you might achieve undo redo history with atoms?

[dai-shi]

Something like this:

const initialValue = 'hello'

const historyAtom = atom({
  history: [initialValue],
  index: 0,
})

const valueAtom = atom(
  (get) => {
    const { history, index } = get(historyAtom)
    return history[index]
  },
  (get, set, action) => {
    const { history, index } = get(historyAtom)
    if (action.type === 'update') {
      set(historyAtom, {
        history: [...history.slice(0, index + 1), action.value],
        index: index + 1,
      })
    } else if (action.type === 'undo' && index > 0) {
      set(historyAtom, { history, index: index - 1 })
    } else if (action.type === 'redo' && index < history.length - 1) {
      set(historyAtom, { history, index: index + 1 })
    }
  }
)