From ce1082ec9fe917dbdeb1965fa0eb0a8325f619b5 Mon Sep 17 00:00:00 2001
From: Simon Knott <info@simonknott.de>
Date: Mon, 6 Oct 2025 15:16:01 +0200
Subject: [PATCH] fix: `exposeBinding` should work in parallel (#37721)

---
 .../src/server/browserContext.ts              | 22 +++++++++----------
 tests/page/page-expose-function.spec.ts       | 11 ++++++++++
 2 files changed, 22 insertions(+), 11 deletions(-)

diff --git a/packages/playwright-core/src/server/browserContext.ts b/packages/playwright-core/src/server/browserContext.ts
index 1866e05a21..9edfd3a43f 100644
--- a/packages/playwright-core/src/server/browserContext.ts
+++ b/packages/playwright-core/src/server/browserContext.ts
@@ -93,7 +93,7 @@ export abstract class BrowserContext extends SdkObject {
   _closeReason: string | undefined;
   readonly clock: Clock;
   _clientCertificatesProxy: ClientCertificatesProxy | undefined;
-  private _playwrightBindingExposed = false;
+  private _playwrightBindingExposed?: Promise<void>;
   readonly dialogManager: DialogManager;
 
   constructor(browser: Browser, options: types.BrowserContextOptions, browserContextId: string | undefined) {
@@ -304,19 +304,19 @@ export abstract class BrowserContext extends SdkObject {
   }
 
   async exposePlaywrightBindingIfNeeded() {
-    if (this._playwrightBindingExposed)
-      return;
-    this._playwrightBindingExposed = true;
-    await this.doExposePlaywrightBinding();
+    this._playwrightBindingExposed ??= (async () => {
+      await this.doExposePlaywrightBinding();
 
-    this.bindingsInitScript = PageBinding.createInitScript();
-    this.initScripts.push(this.bindingsInitScript);
-    await this.doAddInitScript(this.bindingsInitScript);
-    await this.safeNonStallingEvaluateInAllFrames(this.bindingsInitScript.source, 'main');
+      this.bindingsInitScript = PageBinding.createInitScript();
+      this.initScripts.push(this.bindingsInitScript);
+      await this.doAddInitScript(this.bindingsInitScript);
+      await this.safeNonStallingEvaluateInAllFrames(this.bindingsInitScript.source, 'main');
+    })();
+    return await this._playwrightBindingExposed;
   }
 
-  needsPlaywrightBinding() {
-    return this._playwrightBindingExposed;
+  needsPlaywrightBinding(): boolean {
+    return this._playwrightBindingExposed !== undefined;
   }
 
   async exposeBinding(progress: Progress, name: string, needsHandle: boolean, playwrightBinding: frames.FunctionWithSource, forClient?: unknown): Promise<PageBinding> {
diff --git a/tests/page/page-expose-function.spec.ts b/tests/page/page-expose-function.spec.ts
index e9334c4df0..8bafdff2b3 100644
--- a/tests/page/page-expose-function.spec.ts
+++ b/tests/page/page-expose-function.spec.ts
@@ -292,3 +292,14 @@ it('should fail with busted Array.prototype.toJSON', async ({ page }) => {
 
   expect.soft(await page.evaluate(() => ([] as any).toJSON())).toBe('"[]"');
 });
+
+it('exposeBinding should work in parallel', { annotation: { type: 'issue', description: 'https://github.com/microsoft/playwright/issues/37712' } }, async ({ page }) => {
+  await Promise.all([
+    page.exposeBinding('foo', () => 42),
+    page.exposeBinding('bar', () => 42),
+  ]);
+  await page.evaluate(() => {
+    (window as any).foo();
+    (window as any).bar();
+  });
+});