From e73cb22f870cc2316c7265fe4f4f80ee3d08aba8 Mon Sep 17 00:00:00 2001
From: Cody Coljee-Gray <68203+codr@users.noreply.github.com>
Date: Fri, 26 Jun 2026 20:57:40 -0700
Subject: [PATCH] fix(browser): Accept precisely-typed GrowthBook class in
 growthbookIntegration
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`growthbookIntegration({ growthbookClass: GrowthBook })` — the call shown in the
integration's own docs — did not type-check against the real
`@growthbook/growthbook` class, forcing consumers to cast. The parameter was
typed as `new (...args: unknown[]) => GrowthBook`, and a narrow constructor
(`constructor(options?: Options)`) is not assignable to an `unknown[]`
constructor.

The integration only reads `growthbookClass.prototype`, so type the parameter
structurally as `{ prototype: GrowthBook }`. This accepts a real GrowthBook
class with no cast, still rejects classes missing `isOn`/`getFeatureValue`, uses
no `any`, and makes the internal prototype cast redundant.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 .../featureFlags/growthbook/types.ts          |  4 +-
 .../growthbook/integration.test.ts            | 37 +++++++++++++++++++
 .../integrations/featureFlags/growthbook.ts   |  4 +-
 3 files changed, 41 insertions(+), 4 deletions(-)
 create mode 100644 packages/browser/test/integrations/featureFlags/growthbook/integration.test.ts

diff --git a/packages/browser/src/integrations/featureFlags/growthbook/types.ts b/packages/browser/src/integrations/featureFlags/growthbook/types.ts
index 5a852d633da9..94d5a8ab2294 100644
--- a/packages/browser/src/integrations/featureFlags/growthbook/types.ts
+++ b/packages/browser/src/integrations/featureFlags/growthbook/types.ts
@@ -3,5 +3,5 @@ export interface GrowthBook {
   getFeatureValue(this: GrowthBook, featureKey: string, defaultValue: unknown, ...rest: unknown[]): unknown;
 }
 
-// We only depend on the surface we wrap; constructor args are irrelevant here.
-export type GrowthBookClass = new (...args: unknown[]) => GrowthBook;
+// We only depend on the surface we wrap, so accept any class whose prototype matches.
+export type GrowthBookClass = { prototype: GrowthBook };
diff --git a/packages/browser/test/integrations/featureFlags/growthbook/integration.test.ts b/packages/browser/test/integrations/featureFlags/growthbook/integration.test.ts
new file mode 100644
index 000000000000..b689d0a436a8
--- /dev/null
+++ b/packages/browser/test/integrations/featureFlags/growthbook/integration.test.ts
@@ -0,0 +1,37 @@
+import { getCurrentScope } from '@sentry/core/browser';
+import { afterEach, describe, expect, it } from 'vitest';
+import { growthbookIntegration } from '../../../../src/integrations/featureFlags/growthbook';
+
+describe('growthbookIntegration', () => {
+  afterEach(() => {
+    getCurrentScope().clear();
+  });
+
+  it('accepts a precisely-typed GrowthBook class without a cast and captures boolean evaluations', () => {
+    class MockGrowthBook {
+      public constructor(_options?: { apiHost: string }) {}
+
+      public isOn(_key: string): boolean {
+        return true;
+      }
+
+      public getFeatureValue(_key: string, _defaultValue: unknown): unknown {
+        return false;
+      }
+    }
+
+    const integration = growthbookIntegration({
+      growthbookClass: MockGrowthBook,
+    });
+    integration.setupOnce?.();
+
+    const growthbook = new MockGrowthBook();
+    growthbook.isOn('my-feature');
+    growthbook.getFeatureValue('my-other-feature', true);
+
+    expect(getCurrentScope().getScopeData().contexts.flags?.values).toEqual([
+      { flag: 'my-feature', result: true },
+      { flag: 'my-other-feature', result: false },
+    ]);
+  });
+});
diff --git a/packages/core/src/integrations/featureFlags/growthbook.ts b/packages/core/src/integrations/featureFlags/growthbook.ts
index 6f3d4bfe73fd..6193e271e9cc 100644
--- a/packages/core/src/integrations/featureFlags/growthbook.ts
+++ b/packages/core/src/integrations/featureFlags/growthbook.ts
@@ -14,7 +14,7 @@ interface GrowthBookLike {
   getFeatureValue(this: GrowthBookLike, featureKey: string, defaultValue: unknown, ...rest: unknown[]): unknown;
 }
 
-export type GrowthBookClassLike = new (...args: unknown[]) => GrowthBookLike;
+export type GrowthBookClassLike = { prototype: GrowthBookLike };
 
 /**
  * Sentry integration for capturing feature flag evaluations from GrowthBook.
@@ -40,7 +40,7 @@ export const growthbookIntegration: IntegrationFn = defineIntegration(
       name: 'GrowthBook' as const,
 
       setupOnce() {
-        const proto = growthbookClass.prototype as GrowthBookLike;
+        const proto = growthbookClass.prototype;
 
         // Type guard and wrap isOn
         if (typeof proto.isOn === 'function') {