Zustand persist rehydration completes after first render

Direct answer

No to all three. The onRehydrateStorage callback does not fire before the first mounted component reads the store. A selector cannot safely return persisted state during the initial render. Zustand does not provide a synchronous rehydration guarantee across supported releases, even when the underlying storage is synchronous.

Likely explanation vs confirmed behavior

Likely explanation: The persist middleware defers state merging until after store creation, so the initial render cycle completes before rehydration finishes. The middleware treats rehydration as an asynchronous side effect regardless of whether the storage backend is synchronous.

Confirmed behavior: Selectors read synchronously from the current store snapshot. Until rehydration completes and the persisted state is merged, the snapshot reflects the initial state passed to the store creator. The onRehydrateStorage listener is invoked before rehydration begins, and its returned callback runs after rehydration completes—after the initial render.

Steps for this case

1. Add a hydration flag to your store, initialized to false.
2. Set the flag to true inside the onRehydrateStorage callback.
3. Gate components that depend on persisted values behind that flag.

Alternatively, use skipHydration: true and call the returned rehydrate function manually in a useEffect before rendering dependent children.

Version assumptions and verification

This behavior is consistent across Zustand v4 and v5, though the exact onRehydrateStorage callback signature differs between releases. Check your installed version in package.json and inspect the persist middleware source for your release.

To verify the timing in your project, build a minimal store with persist and a mocked localStorage. Log the render order alongside the rehydration callback. You should observe the initial render preceding hydration. If you need to eliminate the initial default-state read entirely, test a skipHydration store with a manual rehydrate call in useEffect.