Implementation:Microsoft Playwright Server Clock

Knowledge Sources	Microsoft_Playwright
Domains	Server, Time
Last Updated	2026-02-12 00:00 GMT

Overview

Concrete tool for emulating and controlling time-related APIs (Date, setTimeout, setInterval, etc.) in browser contexts provided by the Playwright library.

Description

The `Clock` class manages fake clock installation and manipulation within a `BrowserContext`. It injects clock source scripts as init scripts that override `Date`, `setTimeout`, `setInterval`, `requestAnimationFrame`, and related timing APIs. The class provides `install` to set up the fake clock at a specific time, `fastForward` to advance time by a specified number of ticks, `pauseAt` to freeze time at a specific point, `resume` to resume real-time progression, and `uninstall` to remove the clock overrides. Each operation adds an init script to ensure new pages in the context inherit the clock state. The `setFixedTime` and `setSystemTime` methods allow updating the clock without triggering timers.

Usage

Use Server Clock when testing time-dependent functionality, such as animations, debouncing, or scheduled tasks, via Playwright's `page.clock` API.

Code Reference

Source Location

• Repository: Microsoft_Playwright
• File: packages/playwright-core/src/server/clock.ts

Signature

export class Clock {
  constructor(browserContext: BrowserContext);
  async uninstall(progress: Progress): Promise<void>;
  async fastForward(progress: Progress, ticks: number | string): Promise<void>;
  async install(progress: Progress, time: number | string | undefined): Promise<void>;
  async pauseAt(progress: Progress, ticks: number | string): Promise<void>;
  resumeNoReply(): void;
  async setFixedTime(progress: Progress, time: number | string): Promise<void>;
  async setSystemTime(progress: Progress, time: number | string): Promise<void>;
}

Import

import { Clock } from '../server/clock';

I/O Contract

Inputs

Name	Type	Required	Description
browserContext	BrowserContext	Yes	The browser context in which to install the fake clock
progress	Progress	Yes	Progress tracker for cancellation
time	number or string	No	Time value (epoch millis or ISO string) for install/pauseAt
ticks	number or string	Yes (fastForward)	Number of milliseconds or time string to advance

Outputs

Name	Type	Description
(side effect)	void	Clock state installed/modified in all frames of the browser context

Usage Examples

import { Clock } from '../server/clock';

const clock = new Clock(browserContext);
await clock.install(progress, '2024-01-01T00:00:00Z');
await clock.fastForward(progress, 60000); // advance 1 minute
await clock.pauseAt(progress, '2024-01-01T01:00:00Z');
await clock.uninstall(progress);

Related Pages

• Environment:Microsoft_Playwright_Node_Runtime_Environment