SSR & testing

Because a query is plain effector under the hood, fork() + allSettled() work as usual — no special test utilities.

Testing a query

import { fork, allSettled } from 'effector';

const scope = fork();
await allSettled(query.start, { scope, params: 1 });
expect(scope.getState(query.$data)).toEqual(/* ... */);

SSR

const scope = fork();
await allSettled(query.start, { scope, params: req.params });
const html = renderToString(/* app */, scope);
const serialized = serialize(scope); // effector serialize — $data / $status / …

Bindings are scope-aware: React via <Provider value={scope}>, Vue via the EffectorScopePlugin({ scope }).

Transferring the cache (dehydrate / hydrate)

serialize(scope) captures the store state, but the query cache (dedupe / staleAfter) lives outside the scope, so it isn't included. dehydrate snapshots it; hydrate restores it on the client — so cached params hit instead of refetching:

// server — alongside serialize(scope)
const cache = inMemoryCache();
const todos = createQuery({ effect: fetchTodosFx, cache: { adapter: cache } });
// … run queries under the scope …
const payload = { values: serialize(scope), cache: dehydrate(cache) };

// client
hydrate(cache, payload.cache); // warm the cache (storedAt preserved → staleAfter ages correctly)
const scope = fork({ values: payload.values }); // $data restored — no loading flash

Only adapters that can enumerate entries (e.g. inMemoryCache) are dehydratable; web-storage adapters already persist themselves.

Persisting on the client

Two complementary ways to keep data across reloads in the browser:

• Cache layer — use localStorageCache / sessionStorageCache as the adapter; the query cache survives reloads (and version lets you invalidate old data).

• Store layer — persist $data directly with effector-storage:

  import { persist } from 'effector-storage/local';
  persist({ store: todosQuery.$data as StoreWritable<Todo[] | null>, key: 'todos:data' });

  ($data is read-only in the public type but writable at runtime — cast for persist.)

Full runnable flow: examples/ssr.ts.

Notes

• Sourced config (Store for concurrency / retry.times / cache.staleAfter / enabled) is fork-correct — each scope sees its own value.
• Cache adapters hold state outside the effector scope; for isolated SSR build queries per request (as usual), or pass a fresh adapter.
• In-flight AbortControllers are tracked per query instance; avoid sharing one query instance across concurrent SSR requests if you also call cancel.