From d0c840f6390e3693fce199507981716be3df62f9 Mon Sep 17 00:00:00 2001
From: Max Schmitt <max@schmitt.mx>
Date: Fri, 2 Aug 2024 15:27:54 +0200
Subject: [PATCH] fix(clock): mock time in Event.prototype.timeStamp (#31986)

Ideally we generate the timestamp when the Event gets created. This
patch adds a best-effort logic, since we can't override the constructor
of natively created events, e.g. `MouseEvent`.

Fixes https://github.com/microsoft/playwright/issues/31924
---
 docs/src/clock.md                                    |  1 +
 .../playwright-core/src/server/injected/clock.ts     |  8 ++++++++
 tests/library/clock.spec.ts                          | 12 ++++++++++++
 3 files changed, 21 insertions(+)

diff --git a/docs/src/clock.md b/docs/src/clock.md
index a515d46d50..ea14941d82 100644
--- a/docs/src/clock.md
+++ b/docs/src/clock.md
@@ -31,6 +31,7 @@ The recommended approach is to use `setFixedTime` to set the time to a specific
   - `requestIdleCallback`
   - `cancelIdleCallback`
   - `performance`
+  - `Event.timeStamp`
 :::
 
 ## Test with predefined time
diff --git a/packages/playwright-core/src/server/injected/clock.ts b/packages/playwright-core/src/server/injected/clock.ts
index afce525be1..48cc9276a2 100644
--- a/packages/playwright-core/src/server/injected/clock.ts
+++ b/packages/playwright-core/src/server/injected/clock.ts
@@ -697,6 +697,14 @@ export function install(globalObject: WindowOrWorkerGlobalScope, config: Install
       (globalObject as any).Intl = api[method]!;
     } else if (method === 'performance') {
       (globalObject as any).performance = api[method]!;
+      const kEventTimeStamp = Symbol('playwrightEventTimeStamp');
+      Object.defineProperty(Event.prototype, 'timeStamp', {
+        get() {
+          if (!this[kEventTimeStamp])
+            this[kEventTimeStamp] = api.performance?.now();
+          return this[kEventTimeStamp];
+        }
+      });
     } else {
       (globalObject as any)[method] = (...args: any[]) => {
         return (api[method] as any).apply(api, args);
diff --git a/tests/library/clock.spec.ts b/tests/library/clock.spec.ts
index 9fd8426a92..90279fd893 100644
--- a/tests/library/clock.spec.ts
+++ b/tests/library/clock.spec.ts
@@ -1060,6 +1060,18 @@ it.describe('stubTimers', () => {
     expect(prev).toBe(0);
   });
 
+  it('replace Event.prototype.timeStamp', async ({ install }) => {
+    it.info().annotations.push({ type: 'issue', description: 'https://github.com/microsoft/playwright/issues/31924' });
+    const clock = install();
+    await clock.runFor(1000);
+    const event1 = new Event('foo');
+    expect(event1.timeStamp).toBe(1000);
+    await clock.runFor(1000);
+    const event2 = new Event('foo');
+    expect(event2.timeStamp).toBe(2000);
+    expect(event1.timeStamp).toBe(1000);
+  });
+
   it('uninstalls global performance.now', async ({ install }) => {
     const oldNow = performance.now;
     const clock = install();