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Stop JavaScript coverage
A minimal Puppeteer flow is to start coverage, load and exercise the page, then stop coverage and retain the returned reports:
await page.coverage.startJSCoverage();
await page.goto('https://example.com');
// Perform the interactions whose JavaScript usage you want to collect.
const jsCoverage = await page.coverage.stopJSCoverage();startJSCoverage() and stopJSCoverage() are asynchronous; await them so collection has started before navigation or interaction, and so the report is available when stopping. See the Puppeteer Coverage API.
What the stop call returns
stopJSCoverage() resolves to an array with one report entry for each reported script. Entries include script text and executed ranges, which you can inspect or pass to a coverage conversion tool. The stop call marks the end of collection; it does not reconstruct data Chrome has already discarded.
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Collect coverage across multiple pages
The resetOnNavigation option defaults to true. Setting it to false does not guarantee that coverage survives navigation: Chrome can discard the prior page’s JavaScript execution environment and its coverage data. For a multi-page journey, stop before leaving each page, start a fresh collection on the next page, and merge the returned entries in your application.
- Start JavaScript coverage on the current page.
- Perform the interactions to measure, then call
stopJSCoverage()before navigating away. - Navigate to the next page and start coverage again.
- Combine the per-page report entries in your own reporting pipeline.
Include anonymous scripts when needed
By default, coverage omits scripts without an associated URL, including code created with eval or new Function. Start collection with reportAnonymousScripts: true to include them:
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await page.coverage.startJSCoverage({ reportAnonymousScripts: true });Puppeteer documents generated URLs in the form debugger://VM for these scripts unless a //# sourceURL comment provides a URL. Enable this option when anonymous code matters to your analysis; otherwise, the default avoids those entries.
Read or export the coverage data
Coverage ranges describe executed portions of each script. Puppeteer’s API example calculates used bytes by summing range.end - range.start - 1 across a script’s ranges, then compares that total with the script text length. Treat that as a range-based byte calculation, not a complete measure of runtime cost or performance.
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For an Istanbul-consumable format, the API reference points to puppeteer-to-istanbul. JavaScript and CSS coverage are separate collections: stopping CSS coverage requires its own call, stopCSSCoverage().
Troubleshooting
- The stop call fails or there is no report. Start JavaScript coverage on the same page first, and await the start call before attempting to stop it.
- Coverage seems missing after navigation. Do not rely on
resetOnNavigation: falseto preserve execution data. Stop before navigation, restart on the next page, and merge the reports. - Code created with
evaldoes not appear. Start coverage withreportAnonymousScripts: true; anonymous scripts are excluded by default. - You expected CSS entries in the JavaScript report. Start and stop CSS coverage separately;
stopJSCoverage()returns JavaScript coverage.
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