feat: add page.stealth_evaluate() for undetectable JS execution (#108)

Extract CDP isolated world classes from humanize layer into standalone
stealth_eval module. Attach page.stealth_evaluate(expression) to every
page automatically — runs JS in a CDP isolated world with clean
Error.stack traces and full variable isolation from main world JS.

js/README.md

@@ -177,6 +177,24 @@ if (newVersion) console.log(`Updated to ${newVersion}`);
 | TLS fingerprint | Mismatch | **Identical to Chrome** |
 | | | **Tested against 30+ detection sites** |
 
+## Stealth Evaluate
+
+`page.stealthEvaluate(expression)` runs JavaScript in a CDP isolated world instead of Playwright's main-world `evaluate()`. This produces clean `Error.stack` traces and full variable isolation from page JS.
+
+```typescript
+const browser = await launch();
+const page = await browser.newPage();
+await page.goto('https://example.com');
+
+// Stealth — clean stack trace, invisible to page JS
+const title = await page.stealthEvaluate('document.title');
+
+// Regular evaluate — unchanged, use for DOM writes
+await page.evaluate(() => { document.body.style.display = 'none'; });
+```
+
+Always available on every page — no flag needed. Returns JSON-serializable values only. The isolated world context auto-recreates after navigation.
+
 ## Configuration
 
 | Env Variable | Default | Description |

js/src/human/index.ts

@@ -19,6 +19,7 @@ import { HumanConfig, resolveConfig, rand, randRange, sleep } from './config.js'
 import { RawMouse, RawKeyboard, humanMove, humanClick, clickTarget, humanIdle } from './mouse.js';
 import { humanType } from './keyboard.js';
 import { scrollToElement } from './scroll.js';
+import { StealthEval } from '../stealth-eval.js';
 
 export { HumanConfig, resolveConfig } from './config.js';
 export { humanMove, humanClick, clickTarget, humanIdle } from './mouse.js';
@@ -29,102 +30,7 @@ export { scrollToElement } from './scroll.js';
 const SELECT_ALL = process.platform === 'darwin' ? 'Meta+a' : 'Control+a';
 
 
-// ============================================================================
-// CDP Isolated World — stealth DOM evaluation
-// ============================================================================
-
-/**
- * Manages a CDP isolated execution context for DOM reads.
- * Produces clean Error.stack traces (no 'eval at evaluate :302:')
- * and is invisible to querySelector monkey-patches in the main world.
- *
- * Context ID is invalidated on navigation and auto-recreated on next call.
- */
-class StealthEval {
-  private cdp: CDPSession | null = null;
-  private contextId: number | null = null;
-  private page: Page;
-
-  constructor(page: Page) {
-    this.page = page;
-  }
-
-  private async ensureCdp(): Promise<CDPSession> {
-    if (!this.cdp) {
-      this.cdp = await this.page.context().newCDPSession(this.page);
-    }
-    return this.cdp;
-  }
-
-  private async createWorld(): Promise<number> {
-    const cdp = await this.ensureCdp();
-    const tree = await cdp.send('Page.getFrameTree');
-    const frameId = tree.frameTree.frame.id;
-    const result = await cdp.send('Page.createIsolatedWorld', {
-      frameId,
-      worldName: '',
-      grantUniveralAccess: true,
-    });
-    const ctxId = result.executionContextId;
-    this.contextId = ctxId;
-    return ctxId;
-  }
-
-  /**
-   * Evaluate a JS expression in the isolated world.
-   * Auto-recreates the world if the context was invalidated (navigation).
-   * Returns the result value, or undefined on failure.
-   */
-  async evaluate(expression: string): Promise<any> {
-    if (this.contextId === null) {
-      await this.createWorld();
-    }
-
-    for (let attempt = 0; attempt < 2; attempt++) {
-      try {
-        const cdp = await this.ensureCdp();
-        const result = await cdp.send('Runtime.evaluate', {
-          expression,
-          contextId: this.contextId!,
-          returnByValue: true,
-        });
-
-        if (result.exceptionDetails) {
-          // Context was likely invalidated by navigation
-          if (attempt === 0) {
-            await this.createWorld();
-            continue;
-          }
-          return undefined;
-        }
-
-        return result.result?.value;
-      } catch {
-        if (attempt === 0) {
-          this.contextId = null;
-          try {
-            await this.createWorld();
-          } catch {
-            return undefined;
-          }
-          continue;
-        }
-        return undefined;
-      }
-    }
-    return undefined;
-  }
-
-  /** Mark context as stale — call after navigation. */
-  invalidate(): void {
-    this.contextId = null;
-  }
-
-  /** Get the underlying CDP session (reused for Input.dispatchKeyEvent etc.). */
-  async getCdpSession(): Promise<CDPSession> {
-    return this.ensureCdp();
-  }
-}
+// StealthEval is defined in stealth-eval.ts and imported at the top of this file.
 
 
 // ============================================================================
@@ -163,7 +69,8 @@ async function isInputElement(
             || el.getAttribute('contenteditable') === 'true';
         })()
       `);
-      return !!result;
+      if (result !== undefined && result !== null) return !!result;
+      // undefined/null = CDP failed, fall through to page.evaluate
     } catch {
       // Fall through to page.evaluate
     }
@@ -197,7 +104,8 @@ async function isSelectorFocused(
           return el === document.activeElement;
         })()
       `);
-      return !!result;
+      if (result !== undefined && result !== null) return !!result;
+      // undefined/null = CDP failed, fall through to page.evaluate
     } catch {
       // Fall through to page.evaluate
     }
@@ -246,9 +154,9 @@ function patchPage(page: Page, cfg: HumanConfig, cursor: CursorState): void {
   (page as any)._original = originals;
   (page as any)._humanCfg = cfg;
 
-  // --- Stealth infrastructure ---
-  const stealth = new StealthEval(page);
-  (page as any)._stealth = stealth;
+  // --- Stealth infrastructure (reuse if already attached by stealth-eval) ---
+  const stealth = (page as any)._stealthWorld ?? new StealthEval(page);
+  (page as any)._stealthWorld = stealth;
 
   // CDP session for shift symbol typing (lazy-initialized, reuses stealth's session)
   let cdpSession: CDPSession | null = null;

js/src/playwright.ts

@@ -67,6 +67,10 @@ export async function launch(options: LaunchOptions = {}): Promise<Browser> {
     patchBrowser(browser, cfg);
   }
 
+  // Stealth evaluate — always attached
+  const { patchBrowser: patchStealthEval } = await import('./stealth-eval.js');
+  patchStealthEval(browser);
+
   return browser;
 }
 
@@ -132,6 +136,10 @@ export async function launchContext(
     patchContext(context, cfg);
   }
 
+  // Stealth evaluate — always attached
+  const { patchContext: patchStealthEvalCtx } = await import('./stealth-eval.js');
+  patchStealthEvalCtx(context);
+
   return context;
 }
 
@@ -197,6 +205,10 @@ export async function launchPersistentContext(
     patchContext(context, cfg);
   }
 
+  // Stealth evaluate — always attached
+  const { patchContext: patchStealthEvalCtx2 } = await import('./stealth-eval.js');
+  patchStealthEvalCtx2(context);
+
   return context;
 }
 

js/src/stealth-eval.ts

@@ -0,0 +1,161 @@
+/**
+ * Stealth evaluate — run JS in a CDP isolated world.
+ *
+ * Provides page.stealthEvaluate(expression) on every page returned by
+ * cloakbrowser launch functions.  Produces clean Error.stack traces (no
+ * `eval at evaluate :302:` leak) and full variable isolation from main
+ * world JS.  Context auto-recreates after navigation.
+ *
+ * The same StealthEval instances are reused by the humanize layer
+ * (human/index.ts) for stealth DOM queries.
+ */
+
+import type { Browser, BrowserContext, Page, CDPSession } from 'playwright-core';
+
+
+// ============================================================================
+// Isolated world class
+// ============================================================================
+
+/**
+ * Manages a CDP isolated execution context for DOM reads.
+ * Produces clean Error.stack traces (no 'eval at evaluate :302:')
+ * and is invisible to querySelector monkey-patches in the main world.
+ *
+ * Context ID is invalidated on navigation and auto-recreated on next call.
+ */
+export class StealthEval {
+  private cdp: CDPSession | null = null;
+  private contextId: number | null = null;
+  private page: Page;
+
+  constructor(page: Page) {
+    this.page = page;
+  }
+
+  private async ensureCdp(): Promise<CDPSession> {
+    if (!this.cdp) {
+      this.cdp = await this.page.context().newCDPSession(this.page);
+    }
+    return this.cdp;
+  }
+
+  private async createWorld(): Promise<number> {
+    const cdp = await this.ensureCdp();
+    const tree = await cdp.send('Page.getFrameTree');
+    const frameId = tree.frameTree.frame.id;
+    const result = await cdp.send('Page.createIsolatedWorld', {
+      frameId,
+      worldName: '',
+      grantUniveralAccess: true,
+    });
+    const ctxId = result.executionContextId;
+    this.contextId = ctxId;
+    return ctxId;
+  }
+
+  /**
+   * Evaluate a JS expression in the isolated world.
+   * Auto-recreates the world if the context was invalidated (navigation).
+   * Returns the result value, or undefined on failure.
+   */
+  async evaluate(expression: string): Promise<any> {
+    if (this.contextId === null) {
+      try {
+        await this.createWorld();
+      } catch {
+        return undefined;
+      }
+    }
+
+    for (let attempt = 0; attempt < 2; attempt++) {
+      try {
+        const cdp = await this.ensureCdp();
+        const result = await cdp.send('Runtime.evaluate', {
+          expression,
+          contextId: this.contextId!,
+          returnByValue: true,
+        });
+
+        if (result.exceptionDetails) {
+          if (attempt === 0) {
+            await this.createWorld();
+            continue;
+          }
+          return undefined;
+        }
+
+        return result.result?.value;
+      } catch {
+        if (attempt === 0) {
+          this.contextId = null;
+          try {
+            await this.createWorld();
+          } catch {
+            return undefined;
+          }
+          continue;
+        }
+        return undefined;
+      }
+    }
+    return undefined;
+  }
+
+  /** Mark context as stale — call after navigation. */
+  invalidate(): void {
+    this.contextId = null;
+  }
+
+  /** Get the underlying CDP session (reused for Input.dispatchKeyEvent etc.). */
+  async getCdpSession(): Promise<CDPSession> {
+    return this.ensureCdp();
+  }
+}
+
+
+// ============================================================================
+// Page / context / browser patching
+// ============================================================================
+
+function patchPage(page: Page): void {
+  if ((page as any).stealthEvaluate) return;
+  const existing = (page as any)._stealthWorld;
+  const stealth = existing instanceof StealthEval ? existing : new StealthEval(page);
+  (page as any)._stealthWorld = stealth;
+  (page as any).stealthEvaluate = stealth.evaluate.bind(stealth);
+}
+
+export function patchContext(context: BrowserContext): void {
+  if ((context as any)._stealthEvalPatched) return;
+  (context as any)._stealthEvalPatched = true;
+  for (const p of context.pages()) {
+    patchPage(p);
+  }
+
+  const origNewPage = context.newPage.bind(context);
+  context.newPage = async (...args: Parameters<BrowserContext['newPage']>) => {
+    const page = await origNewPage(...args);
+    patchPage(page);
+    return page;
+  };
+
+  context.on('page', (page: Page) => patchPage(page));
+}
+
+export function patchBrowser(browser: Browser): void {
+  const origNewContext = browser.newContext.bind(browser);
+  browser.newContext = async (...args: Parameters<Browser['newContext']>) => {
+    const ctx = await origNewContext(...args);
+    patchContext(ctx);
+    return ctx;
+  };
+
+  const origNewPage = browser.newPage.bind(browser);
+  browser.newPage = async (...args: Parameters<Browser['newPage']>) => {
+    const page = await origNewPage(...args);
+    patchContext(page.context());
+    patchPage(page);
+    return page;
+  };
+}

js/src/types.ts

@@ -2,6 +2,13 @@
  * Shared types for cloakbrowser launch wrappers.
  */
 
+declare module 'playwright-core' {
+  interface Page {
+    /** Evaluate JS in a CDP isolated world — clean stack traces, invisible to main-world monkey-patches. */
+    stealthEvaluate(expression: string): Promise<any>;
+  }
+}
+
 export interface LaunchOptions {
   /** Run in headless mode (default: true). */
   headless?: boolean;

js/tests/launch.test.ts

@@ -46,14 +46,17 @@ describe("launchContext (unit)", () => {
   let mockContext: any;
   let mockBrowser: any;
   let mockChromium: any;
+  let origNewContext: any;
   const origEnv = process.env.CLOAKBROWSER_BINARY_PATH;
 
   beforeEach(() => {
     process.env.CLOAKBROWSER_BINARY_PATH = "/fake/chrome";
     const origClose = vi.fn();
-    mockContext = { close: origClose, _origClose: origClose };
+    mockContext = { close: origClose, _origClose: origClose, newPage: vi.fn(), on: vi.fn(), pages: vi.fn().mockReturnValue([]) };
+    origNewContext = vi.fn().mockResolvedValue(mockContext);
     mockBrowser = {
-      newContext: vi.fn().mockResolvedValue(mockContext),
+      newContext: origNewContext,
+      newPage: vi.fn(),
       close: vi.fn(),
     };
     mockChromium = { launch: vi.fn().mockResolvedValue(mockBrowser) };
@@ -75,7 +78,7 @@ describe("launchContext (unit)", () => {
     const { launchContext } = await import("../src/playwright.js");
     await launchContext();
 
-    const ctxArgs = mockBrowser.newContext.mock.calls[0][0];
+    const ctxArgs = origNewContext.mock.calls[0][0];
     expect(ctxArgs.viewport).toEqual(DEFAULT_VIEWPORT);
   });
 
@@ -84,7 +87,7 @@ describe("launchContext (unit)", () => {
     const custom = { width: 1280, height: 720 };
     await launchContext({ viewport: custom });
 
-    const ctxArgs = mockBrowser.newContext.mock.calls[0][0];
+    const ctxArgs = origNewContext.mock.calls[0][0];
     expect(ctxArgs.viewport).toEqual(custom);
   });
 
@@ -92,7 +95,7 @@ describe("launchContext (unit)", () => {
     const { launchContext } = await import("../src/playwright.js");
     await launchContext({ userAgent: "Custom/1.0" });
 
-    const ctxArgs = mockBrowser.newContext.mock.calls[0][0];
+    const ctxArgs = origNewContext.mock.calls[0][0];
     expect(ctxArgs.userAgent).toBe("Custom/1.0");
   });
 
@@ -108,7 +111,7 @@ describe("launchContext (unit)", () => {
     expect(hasTimezoneFlag).toBe(true);
 
     // NOT in newContext() — no CDP emulation
-    const ctxArgs = mockBrowser.newContext.mock.calls[0][0];
+    const ctxArgs = origNewContext.mock.calls[0][0];
     expect(ctxArgs.timezoneId).toBeUndefined();
   });
 
@@ -116,7 +119,7 @@ describe("launchContext (unit)", () => {
     const { launchContext } = await import("../src/playwright.js");
     await launchContext({ colorScheme: "dark" });
 
-    const ctxArgs = mockBrowser.newContext.mock.calls[0][0];
+    const ctxArgs = origNewContext.mock.calls[0][0];
     expect(ctxArgs.colorScheme).toBe("dark");
   });
 
@@ -132,6 +135,84 @@ describe("launchContext (unit)", () => {
   });
 });
 
+// ---------------------------------------------------------------------------
+// stealth_evaluate patching unit tests
+// ---------------------------------------------------------------------------
+
+describe("stealthEvaluate patching (unit)", () => {
+  const origEnv = process.env.CLOAKBROWSER_BINARY_PATH;
+  let mockPage: any;
+  let mockContext: any;
+  let mockBrowser: any;
+
+  beforeEach(() => {
+    process.env.CLOAKBROWSER_BINARY_PATH = "/fake/chrome";
+
+    // Page mock with context() returning the implicit context
+    mockPage = {
+      context: vi.fn(),
+    };
+    // Implicit context created by browser.newPage()
+    mockContext = {
+      pages: vi.fn().mockReturnValue([]),
+      newPage: vi.fn(),
+      on: vi.fn(),
+    };
+    mockPage.context.mockReturnValue(mockContext);
+
+    mockBrowser = {
+      newContext: vi.fn().mockResolvedValue(mockContext),
+      newPage: vi.fn().mockResolvedValue(mockPage),
+      close: vi.fn(),
+    };
+    const mockChromium = { launch: vi.fn().mockResolvedValue(mockBrowser) };
+    vi.doMock("playwright-core", () => ({ chromium: mockChromium }));
+  });
+
+  afterEach(() => {
+    vi.restoreAllMocks();
+    vi.resetModules();
+    if (origEnv) {
+      process.env.CLOAKBROWSER_BINARY_PATH = origEnv;
+    } else {
+      delete process.env.CLOAKBROWSER_BINARY_PATH;
+    }
+  });
+
+  it("page.stealthEvaluate exists after launch + browser.newPage", async () => {
+    const { launch } = await import("../src/playwright.js");
+    const browser = await launch({ headless: true });
+    const page = await browser.newPage();
+
+    expect(typeof (page as any).stealthEvaluate).toBe("function");
+  });
+
+  it("implicit context from browser.newPage is patched for future pages", async () => {
+    const { launch } = await import("../src/playwright.js");
+    const browser = await launch({ headless: true });
+    await browser.newPage();
+
+    // The 'page' event listener should be registered on the implicit context
+    expect(mockContext.on).toHaveBeenCalledWith("page", expect.any(Function));
+    // The context should be marked as patched
+    expect((mockContext as any)._stealthEvalPatched).toBe(true);
+  });
+
+  it("context from browser.newContext patches pages with stealthEvaluate", async () => {
+    const { launch } = await import("../src/playwright.js");
+    const browser = await launch({ headless: true });
+
+    const mockPage2: any = { context: vi.fn().mockReturnValue(mockContext) };
+    mockContext.newPage.mockResolvedValue(mockPage2);
+    mockContext.pages.mockReturnValue([]);
+
+    const ctx = await browser.newContext();
+    const page = await ctx.newPage();
+
+    expect(typeof (page as any).stealthEvaluate).toBe("function");
+  });
+});
+
 describe("launchPersistentContext (unit)", () => {
   let mockContext: any;
   let mockChromium: any;
@@ -139,7 +220,7 @@ describe("launchPersistentContext (unit)", () => {
 
   beforeEach(() => {
     process.env.CLOAKBROWSER_BINARY_PATH = "/fake/chrome";
-    mockContext = { close: vi.fn(), pages: vi.fn().mockReturnValue([]) };
+    mockContext = { close: vi.fn(), pages: vi.fn().mockReturnValue([]), newPage: vi.fn(), on: vi.fn() };
     mockChromium = {
       launchPersistentContext: vi.fn().mockResolvedValue(mockContext),
     };

js/tests/stealth.test.ts

@@ -470,7 +470,7 @@ describe("humanType mixed text with CDP", () => {
 // patchPage stealth wiring
 // =========================================================================
 describe("patchPage stealth infrastructure", () => {
-  it("page._stealth is a StealthEval instance after patching", async () => {
+  it("page._stealthWorld is a StealthEval instance after patching", async () => {
     const { patchPage } = await import("../src/human/index.js");
 
     const page = buildMockPage();
@@ -478,10 +478,10 @@ describe("patchPage stealth infrastructure", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    expect((page as any)._stealth).toBeDefined();
-    expect(typeof (page as any)._stealth.evaluate).toBe("function");
-    expect(typeof (page as any)._stealth.invalidate).toBe("function");
-    expect(typeof (page as any)._stealth.getCdpSession).toBe("function");
+    expect((page as any)._stealthWorld).toBeDefined();
+    expect(typeof (page as any)._stealthWorld.evaluate).toBe("function");
+    expect(typeof (page as any)._stealthWorld.invalidate).toBe("function");
+    expect(typeof (page as any)._stealthWorld.getCdpSession).toBe("function");
   });
 
   it("page._original and page._humanCfg are set", async () => {
@@ -504,7 +504,7 @@ describe("patchPage stealth infrastructure", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     const invalidateSpy = vi.spyOn(stealth, "invalidate");
 
     await page.goto("https://example.com");
@@ -540,7 +540,7 @@ describe("StealthEval lifecycle", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     expect(() => stealth.invalidate()).not.toThrow();
   });
 
@@ -552,7 +552,7 @@ describe("StealthEval lifecycle", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     const session = await stealth.getCdpSession();
     expect(session).toBeDefined();
     expect(typeof session.send).toBe("function");
@@ -587,7 +587,7 @@ describe("StealthEval lifecycle", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     const result = await stealth.evaluate("1 + 1");
     expect(result).toBe(true);
   });
@@ -626,7 +626,7 @@ describe("StealthEval lifecycle", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     const result = await stealth.evaluate("test");
     expect(result).toBe("recovered");
   });
@@ -660,7 +660,7 @@ describe("StealthEval lifecycle", () => {
     const cursor = { x: 0, y: 0, initialized: false };
     patchPage(page as any, cfg, cursor as any);
 
-    const stealth = (page as any)._stealth;
+    const stealth = (page as any)._stealthWorld;
     const result = await stealth.evaluate("broken");
     expect(result).toBeUndefined();
   });
@@ -975,7 +975,7 @@ describeIfSlow("stealth browser: navigation invalidation", () => {
     const browser = await launch({ headless: true, args: ['--humanize'] });
     const page = await browser.newPage();
 
-    expect((page as any)._stealth).toBeDefined();
+    expect((page as any)._stealthWorld).toBeDefined();
 
     await page.goto('https://www.wikipedia.org', { waitUntil: 'domcontentloaded' });
     await sleep(1000);