Lazy store

Hi, is there a way to only initialize the store at the moment that a component has used it? And is there a way to have a callback when there are no active listeners? svelte/store has this and is quite similar to zustand.

My usecase is a graphql subscription that is only needed temporarily.

[dai-shi]

So, if I were to do something like this, it could be non lazy store, but with listener count.

const useStore = create((set, get) => ({
  profile: { loading: true },
  observer: null,
  listeners: 0,
  subscribe: () => {
    let { listeners, observer } = get()
    listeners += 1
    if (listeners === 1) {
      observer = graphqlSubscription.subscribe(profile => set({ profile }))
    }
    set({ listeners, observer })
  },
  unsubscribe: () => {
    let { listeners, observer } = get()
    listeners -= 1
    if (listeners === 0) {
      observer.unsubscribe()
      observer = null
    }
    set({ listeners, observer })
  },
}))

const selectProfile = (state) => state.profile

const useProfile = () => {
  const profile = useStore(selectProfile)
  useEffect(() => {
    useStore.getState().subscribe()
    return () => useStore.getState().unsubscribe()
  }, [])
  return profile
}

Just an idea… There might be a better way, like subscribe function returning unsubscribe function.

[dai-shi]

I’m not sure if I understand what createLazy is like, but in general, we would be strict about making breaking changes and adding new core features, as we think the api is basically complete. A PR for middleware would be appreciated (although, I can’t say for sure if it would be merged at this point.)