docs on the persist middleware v5 API

[dai-shi]

#2659 (comment) @cschanhniem

The discussions label approach makes sense for feature pitches. For anyone browsing this, the docs on the persist middleware v5 API don't mention that storage can be a function returning a sync storage object — the example only shows the object literal form. Could be useful to add a brief note about the functional form for SSR compatibility (where localStorage isn't available during render). That tripped me up recently migrating from v4 partialize + customStorage to v5's API shape.

[dai-shi]

How's #3541?

[3ni8ma]

The v5 persist middleware API is mostly the same but with updated type signatures and a few changes:

import { create } from "zustand"
import { persist, createJSONStorage } from "zustand/middleware"

const useStore = create(
  persist(
    (set, get) => ({
      count: 0,
      increment: () => set(state => ({ count: state.count + 1 })),
    }),
    {
      name: "my-storage-key",
      storage: createJSONStorage(() => localStorage),
      partialize: (state) => ({ count: state.count }),
    }
  )
)

Key v5 changes:

• createJSONStorage is now the recommended way to create storage instead of raw objects
• TypeScript generics improved — you don't need as many manual type annotations
• skipHydration can be called before useStore.persist.rehydrate() for SSR
• onRehydrateStorage callback runs after state is restored from storage

Full docs: https://zustand.docs.pmnd.rs/integrations/persisting-store-data