feat: Add support for the afterTrack stage for hooks.

src/HookRunner.js

@@ -3,6 +3,7 @@ const BEFORE_EVALUATION_STAGE_NAME = 'beforeEvaluation';
 const AFTER_EVALUATION_STAGE_NAME = 'afterEvaluation';
 const BEFORE_IDENTIFY_STAGE_NAME = 'beforeIdentify';
 const AFTER_IDENTIFY_STAGE_NAME = 'afterIdentify';
+const AFTER_TRACK_STAGE_NAME = 'afterTrack';
 
 /**
  * Safely executes a hook stage function, logging any errors.
@@ -125,6 +126,28 @@ function executeAfterIdentify(logger, hooks, hookContext, updatedData, result) {
   }
 }
 
+/**
+ * Executes the 'afterTrack' stage for all registered hooks in reverse order.
+ * @param {{ error: (message: string) => void }} logger The logger instance.
+ * @param {Array<{ afterTrack?: (hookContext: { context: object, data: object, metricValue: number }) => void }>} hooks The array of hook instances.
+ * @param {{ context: object, data: object, metricValue: number }} hookContext The context for the track operation.
+ * @returns {void}
+ */
+function executeAfterTrack(logger, hooks, hookContext) {
+  // This iterates in reverse, versus reversing a shallow copy of the hooks,
+  // for efficiency.
+  for (let hookIndex = hooks.length - 1; hookIndex >= 0; hookIndex -= 1) {
+    const hook = hooks[hookIndex];
+    tryExecuteStage(
+      logger,
+      AFTER_TRACK_STAGE_NAME,
+      getHookName(logger, hook),
+      () => hook?.afterTrack?.(hookContext),
+      undefined
+    );
+  }
+}
+
 /**
  * Factory function to create a HookRunner instance.
  * Manages the execution of hooks for flag evaluations and identify operations.
@@ -203,10 +226,24 @@ function createHookRunner(logger, initialHooks) {
     hooksInternal.push(hook);
   }
 
+  /**
+   * Executes the 'afterTrack' stage for all registered hooks in reverse order.
+   * @param {{ context: object, data: object, metricValue: number }} hookContext The context for the track operation.
+   * @returns {void}
+   */
+  function afterTrack(hookContext) {
+    if (hooksInternal.length === 0) {
+      return;
+    }
+    const hooks = [...hooksInternal];
+    executeAfterTrack(logger, hooks, hookContext);
+  }
+
   return {
     withEvaluation,
     identify,
     addHook,
+    afterTrack,
   };
 }
 

src/__tests__/HookRunner-test.js

@@ -16,6 +16,7 @@ const createTestHook = (name = 'Test Hook') => ({
   afterEvaluation: jest.fn(),
   beforeIdentify: jest.fn(),
   afterIdentify: jest.fn(),
+  afterTrack: jest.fn(),
 });
 
 describe('Given a logger, runner, and hook', () => {
@@ -328,4 +329,121 @@ describe('Given a logger, runner, and hook', () => {
       `An error was encountered in "beforeEvaluation" of the "${hookName}" hook: Error: Specific test error`
     );
   });
+
+  it('should execute afterTrack hooks', () => {
+    const context = { kind: 'user', key: 'user-123' };
+    const key = 'test';
+    const data = { test: 'data' };
+    const metricValue = 42;
+
+    const trackContext = {
+      key,
+      context,
+      data,
+      metricValue,
+    };
+
+    hookRunner.afterTrack(trackContext);
+
+    expect(testHook.afterTrack).toHaveBeenCalledWith(trackContext);
+  });
+
+  it('should handle errors in afterTrack hooks', () => {
+    const errorHook = {
+      getMetadata: jest.fn().mockReturnValue({ name: 'Error Hook' }),
+      afterTrack: jest.fn().mockImplementation(() => {
+        throw new Error('Hook error');
+      }),
+    };
+
+    const errorHookRunner = createHookRunner(logger, [errorHook]);
+
+    errorHookRunner.afterTrack({
+      key: 'test',
+      context: { kind: 'user', key: 'user-123' },
+    });
+
+    expect(logger.error).toHaveBeenCalledWith(
+      expect.stringContaining('An error was encountered in "afterTrack" of the "Error Hook" hook: Error: Hook error')
+    );
+  });
+
+  it('should skip afterTrack execution if there are no hooks', () => {
+    const emptyHookRunner = createHookRunner(logger, []);
+
+    emptyHookRunner.afterTrack({
+      key: 'test',
+      context: { kind: 'user', key: 'user-123' },
+    });
+
+    expect(logger.error).not.toHaveBeenCalled();
+  });
+
+  it('executes hook stages in the specified order', () => {
+    const beforeEvalOrder = [];
+    const afterEvalOrder = [];
+    const beforeIdentifyOrder = [];
+    const afterIdentifyOrder = [];
+    const afterTrackOrder = [];
+
+    const createMockHook = id => ({
+      getMetadata: jest.fn().mockReturnValue({ name: `Hook ${id}` }),
+      beforeEvaluation: jest.fn().mockImplementation((_context, data) => {
+        beforeEvalOrder.push(id);
+        return data;
+      }),
+      afterEvaluation: jest.fn().mockImplementation((_context, data) => {
+        afterEvalOrder.push(id);
+        return data;
+      }),
+      beforeIdentify: jest.fn().mockImplementation((_context, data) => {
+        beforeIdentifyOrder.push(id);
+        return data;
+      }),
+      afterIdentify: jest.fn().mockImplementation((_context, data) => {
+        afterIdentifyOrder.push(id);
+        return data;
+      }),
+      afterTrack: jest.fn().mockImplementation(() => {
+        afterTrackOrder.push(id);
+      }),
+    });
+
+    const hookA = createMockHook('a');
+    const hookB = createMockHook('b');
+    const hookC = createMockHook('c');
+
+    const runner = createHookRunner(logger, [hookA, hookB]);
+    runner.addHook(hookC);
+
+    // Test evaluation order
+    runner.withEvaluation('flagKey', { kind: 'user', key: 'bob' }, 'default', () => ({
+      value: false,
+      reason: { kind: 'ERROR', errorKind: 'FLAG_NOT_FOUND' },
+      variationIndex: null,
+    }));
+
+    // Test identify order
+    const identifyCallback = runner.identify({ kind: 'user', key: 'bob' }, 1000);
+    identifyCallback({ status: 'completed' });
+
+    // Test track order
+    runner.afterTrack({
+      key: 'test',
+      context: { kind: 'user', key: 'bob' },
+      data: { test: 'data' },
+      metricValue: 42,
+    });
+
+    // Verify evaluation hooks order
+    expect(beforeEvalOrder).toEqual(['a', 'b', 'c']);
+    expect(afterEvalOrder).toEqual(['c', 'b', 'a']);
+
+    // Verify identify hooks order
+    expect(beforeIdentifyOrder).toEqual(['a', 'b', 'c']);
+    expect(afterIdentifyOrder).toEqual(['c', 'b', 'a']);
+
+    // Verify track hooks order
+    expect(afterTrackOrder).toEqual(['c', 'b', 'a']);
+  });
 });

src/__tests__/LDClient-hooks-test.js

@@ -225,4 +225,30 @@ describe('LDClient Hooks Integration', () => {
       });
     });
   });
+
+  it('should execute afterTrack hooks when tracking events', async () => {
+    const testHook = {
+      beforeEvaluation: jest.fn(),
+      afterEvaluation: jest.fn(),
+      beforeIdentify: jest.fn(),
+      afterIdentify: jest.fn(),
+      afterTrack: jest.fn(),
+      getMetadata() {
+        return {
+          name: 'test hook',
+        };
+      },
+    };
+
+    await withClient(initialContext, {}, [testHook], async client => {
+      client.track('test', { test: 'data' }, 42);
+
+      expect(testHook.afterTrack).toHaveBeenCalledWith({
+        key: 'test',
+        context: { kind: 'user', key: 'user-key-initial' },
+        data: { test: 'data' },
+        metricValue: 42,
+      });
+    });
+  });
 });

src/index.js

@@ -428,6 +428,7 @@ function initialize(env, context, specifiedOptions, platform, extraOptionDefs) {
       e.metricValue = metricValue;
     }
     enqueueEvent(e);
+    hookRunner.afterTrack({ context, key, data, metricValue });
   }
 
   function connectStream() {

typings.d.ts

@@ -127,6 +127,29 @@ declare module 'launchdarkly-js-sdk-common' {
     status: IdentifySeriesStatus;
   }
 
+  /**
+   * Contextual information provided to track stages.
+   */
+  export interface TrackSeriesContext {
+    /**
+     * The key for the event being tracked.
+     */
+    readonly key: string;
+    /**
+     * The context associated with the track operation.
+     */
+    readonly context: LDContext;
+    /**
+     * The data associated with the track operation.
+     */
+    readonly data?: unknown;
+    /**
+     * The metric value associated with the track operation.
+     */
+    readonly metricValue?: number;
+  }
+
+
   /**
    * Interface for extending SDK functionality via hooks.
    */
@@ -216,6 +239,15 @@ declare module 'launchdarkly-js-sdk-common' {
       data: IdentifySeriesData,
       result: IdentifySeriesResult,
     ): IdentifySeriesData;
+
+    /**
+     * This method is called during the execution of the track process after the event
+     * has been enqueued.
+     *
+     * @param hookContext Contains information about the track operation being performed. This is not
+     *  mutable.
+     */
+    afterTrack?(hookContext: TrackSeriesContext): void;
   }
 
   /**