allow onFeatureEvaluated callback

Author: zhiyuanliang-ms

sdk/feature-management/src/featureManager.ts

@@ -14,6 +14,7 @@ import { isTargetedGroup, isTargetedPercentile, isTargetedUser } from "./common/
 export class FeatureManager implements IFeatureManager {
     #provider: IFeatureFlagProvider;
     #featureFilters: Map<string, IFeatureFilter> = new Map();
+    #onFeatureEvaluated?: (event: EvaluationResult) => void;
 
     constructor(provider: IFeatureFlagProvider, options?: FeatureManagerOptions) {
         this.#provider = provider;
@@ -24,6 +25,8 @@ export class FeatureManager implements IFeatureManager {
         for (const filter of [...builtinFilters, ...(options?.customFilters ?? [])]) {
             this.#featureFilters.set(filter.name, filter);
         }
+
+        this.#onFeatureEvaluated = options?.onFeatureEvaluated;
     }
 
     async listFeatureNames(): Promise<string[]> {
@@ -164,9 +167,6 @@ export class FeatureManager implements IFeatureManager {
             }
         }
 
-        // TODO: send telemetry for variant assignment reason in the future.
-        console.log(`Variant assignment for feature ${featureName}: ${variantDef?.name ?? "default"} (${reason})`);
-
         if (variantDef?.configuration_reference !== undefined) {
             console.warn("Configuration reference is not supported yet.");
         }
@@ -183,12 +183,24 @@ export class FeatureManager implements IFeatureManager {
             }
         }
 
+        if (this.#onFeatureEvaluated !== undefined) {
+            this.#onFeatureEvaluated(result);
+        }
+
         return result;
     }
 }
 
 interface FeatureManagerOptions {
+    /**
+     * The custom filters to be used by the feature manager.
+     */
     customFilters?: IFeatureFilter[];
+
+    /**
+     * The callback function that is called when a feature flag is evaluated.
+     */
+    onFeatureEvaluated?: (event: EvaluationResult) => void;
 }
 
 /**