@stainless-code/persist

Hydration-aware persistence middleware for any reactive store — storage × codec seams, TanStack Store adapters, and a React hydration hook. Store-agnostic via a structural PersistableSource; every "can it do X?" is a one-line composition instead of a feature request.

Install

bun add @stainless-code/persist

Each subpath owns its dependency as an optional peer — import only the entries you use, install the matching peer only when you do:

Subpath	Optional peer
@stainless-code/persist	none (zero-dep core)
@stainless-code/persist/seroval	seroval
@stainless-code/persist/idb	idb-keyval
@stainless-code/persist/tanstack-store	@tanstack/store
@stainless-code/persist/react	react

# only when you use the matching entry
bun add seroval idb-keyval @tanstack/store react

Quick start

import { Store } from "@tanstack/store";
import { createSerovalStorage } from "@stainless-code/persist/seroval";
import { persistStore } from "@stainless-code/persist/tanstack-store";
import { toHydrationSignal } from "@stainless-code/persist";
import { useHydrated } from "@stainless-code/persist/react";

const store = new Store({ theme: "light" });
const persist = persistStore(store, {
  name: "app:prefs:v1",
  storage: createSerovalStorage(() => localStorage),
});
export const prefsHydration = toHydrationSignal(persist);

// in a component:
const { hydrated } = useHydrated(prefsHydration);

Relationship to TanStack Persist / zustand persist

Both TanStack Persist and zustand persist wire a single store library to a single storage with a flat options bag. @stainless-code/persist is a middleware model with a first-class hydration lifecycle: persistence is bound to a structural PersistableSource (getState/setState/subscribe) rather than a specific store, so the same middleware persists TanStack Store, zustand, Redux, or a hand-rolled atom. Three seams — backend (StateStorage), codec (StorageCodec), source (PersistableSource) — make every backend × codec cell a one-line composition. The hydration lifecycle (onHydrate / onFinishHydration / hasHydrated, surfaced via HydrationSignal and useHydrated) gates UI flash without coupling to the store's read path, versioned migrate handles schema evolution, crossTab + onCrossTabRemove syncs tabs, and retryWrite shrinks-or-gives-up on quota errors with a write-generation guard so stale retries never clobber newer state.

---

Extensibility guide

Persistence middleware for any getState/setState/subscribe store (TanStack Store adapters included), built around three seams that make every "can it do X?" a one-line answer instead of a feature request. The full API contract lives in the JSDoc of each module.

Entry points (one subpath = one optional peer)

Subpath	Symbols	Optional peer
@stainless-code/persist	persistSource, PersistApi, createStorage, jsonCodec, identityCodec, registry, HydrationSignal (hydration)	none
@stainless-code/persist/seroval	serovalCodec, createSerovalStorage	seroval
@stainless-code/persist/idb	idbStateStorage, createIdbStorage (structured-clone mode)	idb-keyval
@stainless-code/persist/tanstack-store	persistStore, persistAtom	@tanstack/store (types only)
@stainless-code/persist/react	useHydrated React hook	react

No barrel — importing a subpath is the dependency opt-in.

The three seams

1. Backend (StateStorage<TRaw = string>) — anything with getItem/setItem/removeItem, sync or Promise-returning, string-wire by default, generic for structured backends.

import { createSerovalStorage } from "@stainless-code/persist/seroval";
import { createIdbStorage } from "@stainless-code/persist/idb";
import { createJSONStorage } from "@stainless-code/persist";

createSerovalStorage(() => localStorage); // durable prefs
createSerovalStorage(() => sessionStorage); // per-visit state (dies with the tab)
createIdbStorage(); // IndexedDB, structured-clone mode
createJSONStorage(() => AsyncStorage); // React Native — satisfies StateStorage as-is
// custom: in-memory for tests, remote KV, encrypted wrapper — implement 3 methods

2. Codec (StorageCodec<S, TRaw = string>) — pure encode/decode between the persisted envelope and the backend's wire type.

import {
  jsonCodec,
  identityCodec,
  createStorage,
} from "@stainless-code/persist";
import { serovalCodec } from "@stainless-code/persist/seroval";
import { idbStateStorage } from "@stainless-code/persist/idb";

jsonCodec(); // core default — plain JSON
serovalCodec(); // Set / Map / Date / cycles, inert JSON-shaped output
identityCodec(); // structured-clone backends only — zero serialization
// custom — any pair of pure functions:
const superjsonCodec = { encode: superjson.stringify, decode: superjson.parse }; // class instances via registerCustom
const encryptedCodec = {
  encode: (v) => encrypt(JSON.stringify(v)),
  decode: (raw) => JSON.parse(decrypt(raw)),
};

3. Store source (PersistableSource) — structural, so the middleware persists anything reactive:

import {
  persistStore,
  persistAtom,
} from "@stainless-code/persist/tanstack-store";
import { persistSource } from "@stainless-code/persist";

persistStore(store, opts); // @tanstack/store Store
persistAtom(atom, opts); // writable Atom (replace-merge default)
persistSource({ getState, setState, subscribe }, opts); // zustand-like, redux, hand-rolled

Compose freely: createStorage(backend, codec, options) covers every backend × codec cell. Factory policy: codec factories take the backend as an argument; a backend earns its own factory only when it needs real adaptation (IndexedDB); everything else composes — no factory-per-combination.

Recipes

import { createStorage } from "@stainless-code/persist";
import { idbStateStorage, createIdbStorage } from "@stainless-code/persist/idb";
import { serovalCodec } from "@stainless-code/persist/seroval";
import { persistStore } from "@stainless-code/persist/tanstack-store";

// Encryption at rest over IndexedDB
createStorage(() => idbStateStorage(), encryptedCodec, {
  clearCorruptOnFailure: true,
});

// Legacy string payloads in IDB (written by an older version)
createStorage(() => idbStateStorage(), serovalCodec());

// Namespaced IDB store away from other idb-keyval users
createIdbStorage({ store: createStore("my-db", "persist") });

// Cross-tab sync (localStorage): pair crossTab with onCrossTabRemove when using skipPersist
persistStore(store, {
  name,
  storage,
  crossTab: true,
  onCrossTabRemove: () => store.actions.reset(),
});

// Cross-tab over IDB: no storage events — bridge a BroadcastChannel via crossTabEventTarget

Caveats that matter per backend: async backends (IDB) can't settle hydration before first paint → gate UI on useHydrated (@stainless-code/persist/react); sessionStorage is per-tab (crossTab is meaningless); identityCodec never with string-only backends.

Writing a framework adapter

The React hook (@stainless-code/persist/react) is ~20 lines over HydrationSignal — every adapter is the same shape. The contract (full version on HydrationSignal's JSDoc): subscribe returns an idempotent unsubscribe; each subscribe call is an independent subscription; no initial notification and no payload — pull isHydrated() after attach and on every notification; transitions while detached aren't replayed (the snapshot re-read recovers); render hydrated: true on the server (no storage server-side); null signal = no persistence = hydrated.

import type { HydrationSignal } from "@stainless-code/persist";

// Svelte 5 sketch
export function hydratedRune(signal: HydrationSignal | null) {
  if (!signal)
    return {
      get current() {
        return true;
      },
    };
  const subscribe = createSubscriber((update) =>
    signal.subscribeHydrated(update),
  );
  return {
    get current() {
      subscribe();
      return signal.isHydrated();
    },
  };
}

Lifecycle in one paragraph

persistSource hydrates on create (skip with skipHydration; rehydrate() is awaitable), subscribe-writes on every setState (gated until hydrated; optional trailing throttleMs), and tears down completely via destroy() — required for non-singleton stores. Failures route to onError with a phase (write/hydrate/migrate/crossTab); the console fallback is dev-only. Payloads carry version (→ migrate), timestamp (→ maxAge), and buster; retryWrite implements shrink-or-give-up on quota errors with a write-generation guard so stale retries never clobber newer state.