onSet() handler in effect not triggered when atom initialized via RecoilRoot initializeState or snapshot

RecoilRoot using initializeState:

      <RecoilRoot
        initializeState={({ set }) => set(domainState, props.savedDomainState)}
      >
        <AppRoot root={props.root} />
      </RecoilRoot>

The Atom using an effect:

const domainState = atom({
  key: "domainState",
  default: null,
  effects_UNSTABLE: [syncDomainStorage],
});

The function: syncDomainStorage is only triggered on initial render when I use initializeState, only if I remove initializeState the side-effect function is called when the atom is updated.

Any updates to domainState atom should be triggering the effect, which is not the behavior observed when used along with RecoilRoot initializeState

[notnooblord]

Hey! Thanks for reply @drarmstr .

I’m using cookies from request header to set Atoms state on initial Server-side render. And I want effects_UNSTABLE onSet() to mutate cookie client-side when state changes.

My problem is probably framework-specific since nextjs framework gets ServerSide parameters and passes them to components like this <App {...serversideprops}></App> so initializeState is very helpful. And I couldn’t figure out how to pass current cookie header from request to atom effects_UNSTABLE setSelf 😦

Would’ve been perfect combo to have peristent state in cookies if only onSet() in effects_UNSTABLE could be used with initialState. I’m just using regular useEffect to set a cookie after changing atom state for now.

Added example here. _app.js - here I pass cookies to initializeState on initial server-side render. (Breaks setSelf()) index.js - example of current behaviour.

[drarmstr]

Should be fixed with #1511 and tested with #1519 for 0.6 release.

Note you’ll also be able to initialize atoms using props with the upcoming recoil-sync library and effects instead of initializeState. (https://github.com/facebookexperimental/Recoil/pull/1462/files)