Provide a customer persistence store (FF-2085) (#65)

* bump to commons 3.0.6; add LocalStorageBackedAsyncStore (FF-1980)

* Provide a customer persistence store (FF-2085)

* rename to persistentStore

* docs

Author: leoromanovsky

docs/js-client-sdk.iclientconfig.md

@@ -21,8 +21,10 @@ export interface IClientConfig
 |  [baseUrl?](./js-client-sdk.iclientconfig.baseurl.md) |  | string | _(Optional)_ Base URL of the Eppo API. Clients should use the default setting in most cases. |
 |  [numInitialRequestRetries?](./js-client-sdk.iclientconfig.numinitialrequestretries.md) |  | number | _(Optional)_ Number of additional times the initial configuration request will be attempted if it fails. This is the request typically synchronously waited (via await) for completion. A small wait will be done between requests. (Default: 1) |
 |  [numPollRequestRetries?](./js-client-sdk.iclientconfig.numpollrequestretries.md) |  | number | _(Optional)_ Number of additional times polling for updated configurations will be attempted before giving up. Polling is done after a successful initial request. Subsequent attempts are done using an exponential backoff. (Default: 7) |
+|  [persistentStore?](./js-client-sdk.iclientconfig.persistentstore.md) |  | IAsyncStore<Flag> | _(Optional)_ A custom class to use for storing flag configurations. This is useful for cases where you want to use a different storage mechanism than the default storage provided by the SDK. |
 |  [pollAfterFailedInitialization?](./js-client-sdk.iclientconfig.pollafterfailedinitialization.md) |  | boolean | _(Optional)_ Poll for new configurations even if the initial configuration request failed. (default: false) |
 |  [pollAfterSuccessfulInitialization?](./js-client-sdk.iclientconfig.pollaftersuccessfulinitialization.md) |  | boolean | _(Optional)_ Poll for new configurations (every 30 seconds) after successfully requesting the initial configuration. (default: false) |
 |  [requestTimeoutMs?](./js-client-sdk.iclientconfig.requesttimeoutms.md) |  | number | _(Optional)_ \* Timeout in milliseconds for the HTTPS request for the experiment configuration. (Default: 5000) |
+|  [skipInitialRequest?](./js-client-sdk.iclientconfig.skipinitialrequest.md) |  | boolean | _(Optional)_ Skip the request for new configurations during initialization. (default: false) |
 |  [throwOnFailedInitialization?](./js-client-sdk.iclientconfig.throwonfailedinitialization.md) |  | boolean | _(Optional)_ Throw an error if unable to fetch an initial configuration during initialization. (default: true) |
 

docs/js-client-sdk.iclientconfig.persistentstore.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [@eppo/js-client-sdk](./js-client-sdk.md) &gt; [IClientConfig](./js-client-sdk.iclientconfig.md) &gt; [persistentStore](./js-client-sdk.iclientconfig.persistentstore.md)
+
+## IClientConfig.persistentStore property
+
+A custom class to use for storing flag configurations. This is useful for cases where you want to use a different storage mechanism than the default storage provided by the SDK.
+
+**Signature:**
+
+```typescript
+persistentStore?: IAsyncStore<Flag>;
+```

docs/js-client-sdk.iclientconfig.skipinitialrequest.md

@@ -0,0 +1,13 @@
+<!-- Do not edit this file. It is automatically generated by API Documenter. -->
+
+[Home](./index.md) &gt; [@eppo/js-client-sdk](./js-client-sdk.md) &gt; [IClientConfig](./js-client-sdk.iclientconfig.md) &gt; [skipInitialRequest](./js-client-sdk.iclientconfig.skipinitialrequest.md)
+
+## IClientConfig.skipInitialRequest property
+
+Skip the request for new configurations during initialization. (default: false)
+
+**Signature:**
+
+```typescript
+skipInitialRequest?: boolean;
+```

js-client-sdk.api.md

@@ -5,8 +5,10 @@
 ```ts
 
 import { EppoClient } from '@eppo/js-client-sdk-common';
+import { Flag } from '@eppo/js-client-sdk-common';
 import { IAssignmentEvent } from '@eppo/js-client-sdk-common';
 import { IAssignmentLogger } from '@eppo/js-client-sdk-common';
+import { IAsyncStore } from '@eppo/js-client-sdk-common';
 import { IEppoClient } from '@eppo/js-client-sdk-common';
 
 // @public
@@ -41,9 +43,11 @@ export interface IClientConfig {
     baseUrl?: string;
     numInitialRequestRetries?: number;
     numPollRequestRetries?: number;
+    persistentStore?: IAsyncStore<Flag>;
     pollAfterFailedInitialization?: boolean;
     pollAfterSuccessfulInitialization?: boolean;
     requestTimeoutMs?: number;
+    skipInitialRequest?: boolean;
     throwOnFailedInitialization?: boolean;
 }
 

src/configuration-factory.ts

@@ -1,15 +1,20 @@
 import {
   Flag,
   HybridConfigurationStore,
+  IAsyncStore,
   IConfigurationStore,
   MemoryOnlyConfigurationStore,
   MemoryStore,
 } from '@eppo/js-client-sdk-common';
 
 import { LocalStorageBackedAsyncStore } from './local-storage';
 
-export function configurationStorageFactory(): IConfigurationStore<Flag> {
-  if (hasWindowLocalStorage()) {
+export function configurationStorageFactory(
+  persistenceStore?: IAsyncStore<Flag>,
+): IConfigurationStore<Flag> {
+  if (persistenceStore) {
+    return new HybridConfigurationStore(new MemoryStore<Flag>(), persistenceStore);
+  } else if (hasWindowLocalStorage()) {
     // fallback to window.localStorage if available
     return new HybridConfigurationStore(
       new MemoryStore<Flag>(),

src/index.spec.ts

@@ -563,8 +563,7 @@ describe('initialization options', () => {
 
     it('returns empty assignments pre-initialization by default', async () => {
       returnUfc = () => mockConfigResponse;
-      const client = getInstance();
-      expect(client.getStringAssignment(flagKey, 'subject-10', {}, 'default-value')).toBe(
+      expect(getInstance().getStringAssignment(flagKey, 'subject-10', {}, 'default-value')).toBe(
         'default-value',
       );
       // don't await
@@ -573,12 +572,14 @@ describe('initialization options', () => {
         baseUrl,
         assignmentLogger: mockLogger,
       });
-      expect(client.getStringAssignment(flagKey, 'subject', {}, 'default-value')).toBe(
+      expect(getInstance().getStringAssignment(flagKey, 'subject', {}, 'default-value')).toBe(
         'default-value',
       );
       // Advance time so a poll happened and check again
       await jest.advanceTimersByTimeAsync(POLL_INTERVAL_MS);
-      expect(client.getStringAssignment(flagKey, 'subject', {}, 'default-value')).toBe('control');
+      expect(getInstance().getStringAssignment(flagKey, 'subject', {}, 'default-value')).toBe(
+        'control',
+      );
     });
   });
 });

src/index.ts

@@ -4,6 +4,8 @@ import {
   IEppoClient,
   EppoClient,
   FlagConfigurationRequestParameters,
+  Flag,
+  IAsyncStore,
 } from '@eppo/js-client-sdk-common';
 
 import { configurationStorageFactory } from './configuration-factory';
@@ -65,6 +67,13 @@ export interface IClientConfig {
    */
   numPollRequestRetries?: number;
 
+  /**
+   * A custom class to use for storing flag configurations.
+   * This is useful for cases where you want to use a different storage mechanism
+   * than the default storage provided by the SDK.
+   */
+  persistentStore?: IAsyncStore<Flag>;
+
   /**
    * Skip the request for new configurations during initialization. (default: false)
    */
@@ -73,14 +82,12 @@ export interface IClientConfig {
 
 export { IAssignmentLogger, IAssignmentEvent, IEppoClient } from '@eppo/js-client-sdk-common';
 
-const localStorage = configurationStorageFactory();
-
 /**
  * Client for assigning experiment variations.
  * @public
  */
 export class EppoJSClient extends EppoClient {
-  public static instance: EppoJSClient = new EppoJSClient(localStorage, undefined, true);
+  public static instance: EppoJSClient;
   public static initialized = false;
 
   public getStringAssignment(
@@ -154,6 +161,9 @@ export async function init(config: IClientConfig): Promise<IEppoClient> {
       EppoJSClient.instance.stopPolling();
     }
 
+    const configurationStore = configurationStorageFactory(config.persistentStore);
+    EppoJSClient.instance = new EppoJSClient(configurationStore, undefined, true);
+
     const requestConfiguration: FlagConfigurationRequestParameters = {
       apiKey: config.apiKey,
       sdkName,