In-Memory Feature Store for LaunchDarkly Node SDK

A simple, in-memory implementation of the LaunchDarkly feature store interface for the Node.js server SDK.

Overview

This package provides InMemoryFeatureStore, a persistence layer for the LaunchDarkly Node.js server SDK that stores feature flags in memory. It's useful for:

• Testing - No external dependencies, fast, isolated
• Development - Quick iteration without database setup
• Single-instance apps - When you don't need distributed caching

Installation

npm install launchdarkly-node-server-sdk-memory @launchdarkly/node-server-sdk

Quick Start

import { init } from '@launchdarkly/node-server-sdk';
import { createInMemoryStore } from 'launchdarkly-node-server-sdk-memory';

const store = createInMemoryStore();
const client = init('sdk-key', {
  featureStore: store,
});

await client.waitForInitialization();
const flag = client.variation('flag-key', context, false);

API

InMemoryFeatureStore

Implements the LDFeatureStore interface with the following methods:

all(kind, callback)

Retrieves all items of a given kind (excluding deleted items).

get(kind, key, callback)

Retrieves a single item by kind and key. Returns undefined if not found or deleted.

upsert(kind, item, callback)

Adds or updates an item with version-based conflict resolution. Only replaces if incoming version > stored version.

delete(kind, key, version, callback)

Soft deletes an item by marking it as deleted: true. Only deletes if incoming version > stored version.

init(allData, callback)

Initializes the store, completely replacing existing data.

initialized(callback)

Checks whether the store has been populated with data.

close()

Cleanup method (no-op for in-memory store).

getDescription()

Returns "In-memory feature store".

getInitMetaData()

Returns metadata about the store.

Features

• ✅ Full LDFeatureStore compliance - Implements all required methods
• ✅ Version conflict resolution - Higher versions always win
• ✅ Soft delete pattern - Deleted items are excluded from queries
• ✅ Multiple kinds - Supports features, user segments, contexts, etc.
• ✅ Synchronous callbacks - Calls callbacks immediately (no setImmediate)
• ✅ TypeScript support - Full type definitions included

Limitations

⚠️ This store is not suitable for:

• Multi-instance deployments (no persistence across restarts)
• High-traffic applications (not optimized for performance)
• Production use cases requiring data durability

For production, use @launchdarkly/node-server-sdk-redis, PostgreSQL, or other persistent stores.

Testing

npm test
npm run test:watch

All 20+ tests pass, covering:

• CRUD operations
• Version conflict resolution
• Soft delete behavior
• Initialization
• Multiple kinds
• Edge cases

License

Apache License 2.0