Implementation:Microsoft Playwright CrCoverage

Knowledge Sources	Microsoft_Playwright
Domains	Chromium, Coverage
Last Updated	2026-02-12 00:00 GMT

Overview

Concrete tool for collecting JavaScript and CSS code coverage data from Chromium browsers provided by the Playwright library.

Description

The `CRCoverage` class coordinates JavaScript and CSS coverage collection through two internal classes: `JSCoverage` and `CSSCoverage`. `JSCoverage` uses CDP's `Profiler` and `Debugger` domains to track script execution, collecting precise coverage ranges with optional per-block granularity and script content reset. `CSSCoverage` uses the `CSS` and `DOM` domains to track stylesheet usage. Both support start/stop lifecycle with proper cleanup. The `CRCoverage` facade exposes `startJSCoverage`/`stopJSCoverage` and `startCSSCoverage`/`stopCSSCoverage` methods that race against a `Progress` tracker for cancellation support.

Usage

Use CrCoverage when collecting code coverage metrics from Chromium pages via `page.coverage.startJSCoverage()` and related APIs.

Code Reference

Source Location

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

Signature

export class CRCoverage {
  constructor(client: CRSession);
  async startJSCoverage(progress: Progress, options: channels.PageStartJSCoverageParams): Promise<void>;
  async stopJSCoverage(): Promise<channels.PageStopJSCoverageResult>;
  async startCSSCoverage(progress: Progress, options: channels.PageStartCSSCoverageParams): Promise<void>;
  async stopCSSCoverage(): Promise<channels.PageStopCSSCoverageResult>;
}

Import

import { CRCoverage } from '../server/chromium/crCoverage';

I/O Contract

Inputs

Name	Type	Required	Description
client	CRSession	Yes	CDP session for the target page
progress	Progress	Yes	Progress tracker for cancellation
options	PageStartJSCoverageParams / PageStartCSSCoverageParams	Yes	Coverage options (resetOnNavigation, reportAnonymousScripts)

Outputs

Name	Type	Description
jsCoverage	PageStopJSCoverageResult	Array of JS coverage entries with URL, source, and ranges
cssCoverage	PageStopCSSCoverageResult	Array of CSS coverage entries with URL, source, and ranges

Usage Examples

import { CRCoverage } from '../server/chromium/crCoverage';

const coverage = new CRCoverage(crSession);
await coverage.startJSCoverage(progress, { resetOnNavigation: true });
// ... navigate and interact ...
const jsCoverage = await coverage.stopJSCoverage();
for (const entry of jsCoverage.entries) {
  console.log(`${entry.url}: ${entry.ranges.length} ranges`);
}

Related Pages

• Environment:Microsoft_Playwright_Node_Runtime_Environment