feat: custom storage

__mocks__/setup.ts

@@ -9,7 +9,7 @@ jest.mock('@react-native-async-storage/async-storage', () => mockAsyncStorage);
 /*
  * Mock navigator to avoid undefined access in analytics-connector
  */
-global['navigator'] = { product: 'ReactNative' };
+global['navigator'] = { product: 'ReactNative' } as unknown as Navigator;
 
 /*
  * Mock Native Module

__tests__/client.test.ts

@@ -8,6 +8,7 @@
 import { FetchOptions } from '../src/types/client';
 import { ExposureTrackingProvider } from '../src/types/exposure';
 import { Source } from '../src/types/source';
+import { Storage } from '../src/types/storage';
 import { HttpClient, SimpleResponse } from '../src/types/transport';
 import { ExperimentUser, ExperimentUserProvider } from '../src/types/user';
 import { Variant, Variants } from '../src/types/variant';
@@ -266,7 +267,7 @@
   for (let i = 0; i < 10; i++) {
     client.variant(serverKey);
   }
   const variant = client.variant(serverKey);
 
   expect(trackSpy).toBeCalledTimes(1);
   expect(trackSpy).toHaveBeenCalledWith(
@@ -1012,6 +1013,65 @@
     expect(variant.key).toEqual('on');
     expect(variant2.key).toEqual('on');
   });
+
+  test('start with custom storage', async () => {
+    // Create a custom storage object
+    const storageObject = {};
+    const storage = {
+      get: async (key: string) => storageObject[key],
+      put: async (key: string, value: string) => {
+        storageObject[key] = value;
+      },
+      delete: async (key: string) => {
+        delete storageObject[key];
+      },
+    } as Storage;
+
+    // Create a client with the custom storage object
+    const client = new ExperimentClient(API_KEY, { storage });
+    await client.start({ device_id: 'test_device' });
+
+    // Check that the flags are stored in the storage object
+    const storageKey = `amp-exp-$default_instance-${API_KEY.substring(
+      API_KEY.length - 6,
+    )}`;
+    expect(
+      JSON.parse(storageObject[storageKey + '-flags'])[serverKey],
+    ).toMatchObject({
+      key: serverKey,
+    });
+    // Check that the variant is stored in the storage object
+    expect(JSON.parse(storageObject[storageKey])[serverKey]).toMatchObject({
+      key: 'off',
+    });
+  });
+});
+
+test('fetch with custom storage', async () => {
+  // Create a custom storage object
+  const storageObject = {};
+  const storage = {
+    get: async (key: string) => storageObject[key],
+    put: async (key: string, value: string) => {
+      storageObject[key] = value;
+    },
+    delete: async (key: string) => {
+      delete storageObject[key];
+    },
+  } as Storage;
+
+  // Create a client with the custom storage object
+  const client = new ExperimentClient(API_KEY, { storage });
+  await client.fetch(testUser);
+
+  // Check that the variant is stored in the storage object
+  const storageKey = `amp-exp-$default_instance-${API_KEY.substring(
+    API_KEY.length - 6,
+  )}`;
+  expect(JSON.parse(storageObject[storageKey])[serverKey]).toMatchObject({
+    key: 'on',
+    value: 'on',
+  });
 });
 
 describe('fetch retry with different response codes', () => {

src/experimentClient.ts

@@ -142,7 +142,7 @@ export class ExperimentClient implements Client {
       httpClient,
     );
     // Storage & Caching
-    const storage = new LocalStorage();
+    const storage = this.config.storage || new LocalStorage();
     this.variants = getVariantStorage(
       this.apiKey,
       this.config.instanceName,

src/index.ts

@@ -7,5 +7,6 @@ export { Source } from './types/source';
 export * from './types/user';
 export * from './types/variant';
 export * from './types/exposure';
+export * from './types/storage';
 export { Logger, LogLevel } from './types/logger';
 export { ConsoleLogger } from './logger/consoleLogger';

src/storage/cache.ts

@@ -3,8 +3,6 @@ import { EvaluationFlag, GetVariantsOptions } from '@amplitude/experiment-core';
 import { Storage } from '../types/storage';
 import { Variant } from '../types/variant';
 
-import { LocalStorage } from './local-storage';
-
 export const getVariantStorage = (
   deploymentKey: string,
   instanceName: string,
@@ -22,7 +20,7 @@ export const getVariantStorage = (
 export const getFlagStorage = (
   deploymentKey: string,
   instanceName: string,
-  storage: Storage = new LocalStorage(),
+  storage: Storage,
 ): LoadStoreCache<EvaluationFlag> => {
   const truncatedDeployment = deploymentKey.substring(deploymentKey.length - 6);
   const namespace = `amp-exp-${instanceName}-${truncatedDeployment}-flags`;
@@ -32,7 +30,7 @@ export const getFlagStorage = (
 export const getVariantsOptionsStorage = (
   deploymentKey: string,
   instanceName: string,
-  storage: Storage = new LocalStorage(),
+  storage: Storage,
 ): SingleValueStoreCache<GetVariantsOptions> => {
   const truncatedDeployment = deploymentKey.substring(deploymentKey.length - 6);
   const namespace = `amp-exp-${instanceName}-${truncatedDeployment}-variants-options`;

src/storage/local-storage.ts

@@ -3,7 +3,7 @@ import AsyncStorage from '@react-native-async-storage/async-storage';
 import { Storage } from '../types/storage';
 
 export class LocalStorage implements Storage {
-  async get(key: string): Promise<string> {
+  async get(key: string): Promise<string | null> {
     return await AsyncStorage.getItem(key);
   }
 

src/types/config.ts

@@ -3,6 +3,7 @@ import { FetchHttpClient } from '../transport/http';
 import { ExposureTrackingProvider } from './exposure';
 import { Logger, LogLevel } from './logger';
 import { Source } from './source';
+import { Storage } from './storage';
 import { HttpClient } from './transport';
 import { ExperimentUserProvider } from './user';
 import { Variant, Variants } from './variant';
@@ -146,6 +147,12 @@ export interface ExperimentConfig {
    * (Advanced) Use your own http client.
    */
   httpClient?: HttpClient;
+
+  /**
+   * (Advanced) Use your own storage implementation.
+   * If not provided, the client will use the default local storage implementation, which is AsyncStorage.
+   */
+  storage?: Storage;
 }
 
 /**
@@ -198,4 +205,5 @@ export const Defaults: ExperimentConfig = {
   userProvider: null,
   exposureTrackingProvider: null,
   httpClient: FetchHttpClient,
+  storage: null,
 };

src/types/storage.ts

@@ -1,5 +1,5 @@
 export interface Storage {
-  get(key: string): Promise<string>;
+  get(key: string): Promise<string | null>;
   put(key: string, value: string): Promise<void>;
   delete(key: string): Promise<void>;
 }