Implementation:Puppeteer Puppeteer Cdp Coverage

Property	Value
sources	packages/puppeteer-core/src/cdp/Coverage.ts
domains	Code Coverage, Profiling, CDP
last_updated	2026-02-12 00:00 GMT

Overview

Description

The Coverage module provides methods to gather information about which parts of JavaScript and CSS were actually used by a page. It consists of three main classes:

• Coverage -- The facade class accessible via page.coverage. It delegates to JSCoverage and CSSCoverage for the actual work.
• JSCoverage -- Collects JavaScript coverage using the CDP Profiler and Debugger domains. It tracks script URLs and sources via Debugger.scriptParsed events, starts precise coverage via Profiler.startPreciseCoverage, and computes disjoint coverage ranges when stopped.
• CSSCoverage -- Collects CSS coverage using the CDP CSS and DOM domains. It tracks stylesheets via CSS.styleSheetAdded events and computes coverage ranges from CSS.stopRuleUsageTracking results.

Both JS and CSS coverage support a resetOnNavigation option that clears collected data on page navigation. The module includes a convertToDisjointRanges utility that uses a sweep-line algorithm to merge overlapping coverage ranges into non-overlapping intervals.

Coverage output can be converted to Istanbul-compatible format using the puppeteer-to-istanbul package.

Usage

Coverage is accessed via page.coverage. The typical workflow is: start coverage, navigate to a page, then stop coverage and analyze the results.

Code Reference

Source Location: packages/puppeteer-core/src/cdp/Coverage.ts (508 lines)

Signature:

export class Coverage {
  constructor(client: CDPSession);
  async startJSCoverage(options?: JSCoverageOptions): Promise<void>;
  async stopJSCoverage(): Promise<JSCoverageEntry[]>;
  async startCSSCoverage(options?: CSSCoverageOptions): Promise<void>;
  async stopCSSCoverage(): Promise<CoverageEntry[]>;
}

export class JSCoverage {
  constructor(client: CDPSession);
  async start(options?: JSCoverageOptions): Promise<void>;
  async stop(): Promise<JSCoverageEntry[]>;
}

export class CSSCoverage {
  constructor(client: CDPSession);
  async start(options?: CSSCoverageOptions): Promise<void>;
  async stop(): Promise<CoverageEntry[]>;
}

Import:

import { Coverage, JSCoverage, CSSCoverage } from 'puppeteer-core/lib/cdp/Coverage.js';
import type { CoverageEntry, JSCoverageEntry, JSCoverageOptions, CSSCoverageOptions } from 'puppeteer-core/lib/cdp/Coverage.js';

I/O Contract

Inputs:

Parameter	Type	Required	Description
JSCoverageOptions.resetOnNavigation	boolean	No	Whether to reset coverage on every navigation (default: true)
JSCoverageOptions.reportAnonymousScripts	boolean	No	Whether anonymous scripts (eval, new Function) are reported (default: false)
JSCoverageOptions.includeRawScriptCoverage	boolean	No	Whether to include raw V8 script coverage entries (default: false)
JSCoverageOptions.useBlockCoverage	boolean	No	Whether to collect block-level (true) or function-level (false) coverage (default: true)
CSSCoverageOptions.resetOnNavigation	boolean	No	Whether to reset coverage on every navigation (default: true)

Outputs:

Output	Type	Description
JSCoverageEntry[]	Array<{url, text, ranges, rawScriptCoverage?}>	JavaScript coverage entries with URL, source text, used byte ranges, and optional raw V8 data
CoverageEntry[]	Array<{url, text, ranges}>	CSS coverage entries with URL, stylesheet text, and used byte ranges
ranges	Array<{start: number, end: number}>	Disjoint byte ranges of code that was executed/used

Usage Examples

// Calculate percentage of initially used code
await Promise.all([
  page.coverage.startJSCoverage(),
  page.coverage.startCSSCoverage(),
]);

await page.goto('https://example.com');

const [jsCoverage, cssCoverage] = await Promise.all([
  page.coverage.stopJSCoverage(),
  page.coverage.stopCSSCoverage(),
]);

let totalBytes = 0;
let usedBytes = 0;
const coverage = [...jsCoverage, ...cssCoverage];
for (const entry of coverage) {
  totalBytes += entry.text.length;
  for (const range of entry.ranges) {
    usedBytes += range.end - range.start - 1;
  }
}
console.log(`Bytes used: ${(usedBytes / totalBytes) * 100}%`);

// Include raw V8 script coverage data
await page.coverage.startJSCoverage({
  includeRawScriptCoverage: true,
  resetOnNavigation: false,
});
await page.goto('https://example.com');
const entries = await page.coverage.stopJSCoverage();
for (const entry of entries) {
  console.log(entry.url, entry.rawScriptCoverage);
}

// Report anonymous scripts (eval, new Function)
await page.coverage.startJSCoverage({
  reportAnonymousScripts: true,
});

Related Pages

• Environment:Puppeteer_Puppeteer_Node_18_Runtime