Adds a hook to listen for async storage load (#337)

src/StatsigClient.ts

@@ -120,6 +120,7 @@ export default class StatsigClient implements IHasStatsigInternal, IStatsig {
   private static reactNativeUUID?: UUID;
   private appState: AppState | null = null;
   private currentAppState: AppStateStatus | null = null;
+  private onCacheLoadedForReact: (() => void) | null = null;
 
   private ready: boolean;
   private initCalled = false;
@@ -311,12 +312,15 @@ export default class StatsigClient implements IHasStatsigInternal, IStatsig {
           DiagnosticsKey.OVERALL,
           DiagnosticsEvent.START,
         );
+
         this.initCalled = true;
         if (StatsigAsyncStorage.asyncStorage) {
           await this.identity.initAsync();
           await this.store.loadFromAsyncStorage();
         }
 
+        this.onCacheLoadedForReact?.();
+
         if (
           this.appState &&
           this.appState.addEventListener &&
@@ -882,6 +886,10 @@ export default class StatsigClient implements IHasStatsigInternal, IStatsig {
     }
   }
 
+  public setOnCacheLoadedReactCallback(fn?: (() => void) | null) {
+    this.onCacheLoadedForReact = fn ?? null;
+  }
+
   public static setReactNativeUUID(uuid?: UUID | null): void {
     if (uuid != null) {
       StatsigClient.reactNativeUUID = uuid;