@statesync/persistence

---

@statesync/persistence / createMemoryStorageBackend

Function: createMemoryStorageBackend()

function createMemoryStorageBackend<T>(options): StorageBackendWithMetadata<T> & object;

Defined in: persistence/src/storage/memory-storage.ts:147

Creates an in-memory StorageBackendWithMetadata primarily intended for testing purposes.

This backend stores snapshots entirely in memory with no external dependencies or browser API requirements, making it ideal for unit tests, integration tests, and environments where browser storage is unavailable (e.g., Node.js, SSR).

The returned object extends the standard StorageBackendWithMetadata interface with additional testing utilities for inspecting internal state, resetting storage, and dynamically toggling error injection.

Key features:

• Zero external dependencies -- works in any JavaScript runtime
• Configurable latency simulation for testing async/loading behavior
• Error injection for testing error handling and retry logic
• Quota simulation for testing storage limit scenarios
• Full metadata support matching the IndexedDB backend contract
• Snapshot history tracking for assertion in tests

Type Parameters

Type Parameter	Description
T	The type of the state data stored within snapshot envelopes.

Parameters

Parameter	Type	Description
options	MemoryStorageBackendOptions	Configuration options for the memory backend. All options are optional; the default configuration creates a simple, zero-latency, no-failure in-memory store.

Returns

A StorageBackendWithMetadata instance with additional testing utilities: getSavedSnapshots, getRawData, reset, and setFailMode.

Throws

Throws with the configured error message when failOnSave is enabled and a save operation is attempted.

Throws

Throws with the configured error message when failOnLoad is enabled and a load operation is attempted.

Throws

Throws when the serialized snapshot exceeds maxSizeBytes during a save operation.

Examples

const storage = createMemoryStorageBackend<MyState>();

await storage.save({ revision: '1', data: { count: 42 } });
const snapshot = await storage.load();
expect(snapshot?.data.count).toBe(42);

const storage = createMemoryStorageBackend<MyState>({ latencyMs: 100 });
// Each operation will be delayed by 100ms

const storage = createMemoryStorageBackend<MyState>({
  failOnSave: true,
  errorMessage: 'Disk full',
});

await expect(storage.save(snapshot)).rejects.toThrow('Disk full');

// Toggle failure mode dynamically
storage.setFailMode({ save: false });
await storage.save(snapshot); // succeeds now

const storage = createMemoryStorageBackend<MyState>({
  initialSnapshot: { revision: '1', data: { count: 0 } },
  maxSizeBytes: 1024,
});

const snapshot = await storage.load();
expect(snapshot).not.toBeNull();