Use Puppeteer’s page.coverage API: start collection before the navigation or interaction you want to measure, then call stopJSCoverage() and inspect the returned script text and executed ranges. This guide covers the workflow, options, navigation behavior, and reporting.
Start and stop JavaScript coverage
Coverage is exposed on a Puppeteer Page. Start it before the code paths you want to record run. After the page has loaded and your test interactions are complete, stop collection; the result is an array of coverage entries.
await page.coverage.startJSCoverage();
await page.goto('https://example.com');
// Run the page interactions you want to measure here.
const jsCoverage = await page.coverage.stopJSCoverage();
console.log(jsCoverage);The sequence matters: if you start after navigation or after an interaction, execution that already happened will not be part of that collection. Puppeteer’s Coverage class documentation and startJSCoverage() reference describe the API.
Understand the returned entries
Each entry contains script text and ranges representing code recorded as executed. Puppeteer’s example estimates the share of collected script bytes represented by those ranges:
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let totalBytes = 0;
let usedBytes = 0;
for (const entry of jsCoverage) {
totalBytes += entry.text.length;
for (const range of entry.ranges) {
usedBytes += range.end - range.start - 1;
}
}
const percentUsed = (usedBytes / totalBytes) * 100;
console.log(`Recorded used bytes: ${percentUsed}%`);This is a byte-use calculation over the collected scripts, not a measure of test completeness or code quality. Interpret it in the context of what your test actually exercised. Avoid dividing by zero if your run collected no script text:
const percentUsed = totalBytes === 0 ? 0 : (usedBytes / totalBytes) * 100;The entry and range structure is documented in the stopJSCoverage() reference.
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Choose collection options
startJSCoverage() accepts options that affect granularity, script inclusion, and navigation resets. The documented defaults are summarized below; consult Puppeteer’s JSCoverageOptions reference for the version you use.
| Option | Documented default | Effect |
|---|---|---|
resetOnNavigation |
true |
Resets coverage on navigation. Setting it to false is not a guarantee that coverage survives a navigation; see the navigation section. |
reportAnonymousScripts |
false |
Includes scripts without an associated URL, such as scripts created with eval or new Function. Included scripts generally get a debugger://VM URL unless a //# sourceURL comment provides one. |
includeRawScriptCoverage |
false |
Includes raw V8 script coverage entries in the result. Enable this when a downstream tool needs that raw data. |
useBlockCoverage |
true |
Collects block-level rather than function-level coverage. |
For example, enable anonymous scripts and raw V8 data only when your reporting workflow needs them:
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await page.coverage.startJSCoverage({
resetOnNavigation: true,
reportAnonymousScripts: true,
includeRawScriptCoverage: true,
useBlockCoverage: true,
});Handle navigation explicitly
Do not rely on resetOnNavigation: false to preserve coverage from a page you leave. Chrome may discard the previous page’s JavaScript execution environment, including its coverage data. For dependable multi-page collection, stop before navigating away, start a fresh collection on the next page, and merge the resulting reports yourself. This caveat is documented in the JSCoverageOptions reference.
- Start coverage before exercising the current page.
- Complete the interactions for that page, then call
stopJSCoverage()and retain its entries. - Navigate to the next page and start a new collection.
- Repeat, then merge or report the collected entries in your own downstream workflow.
Send coverage to Istanbul
Puppeteer points to puppeteer-to-istanbul as a way to convert coverage output into a format consumable by Istanbul. The exact conversion and Istanbul configuration depend on your reporting setup; the Puppeteer API reference does not prescribe a universal pipeline.
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Troubleshoot coverage collection
- No or unexpectedly little coverage: Start collection before navigation and before the interaction under test. Stopping returns only what was recorded during the active collection.
- Coverage appears to disappear after navigation: Chrome can discard the prior page’s execution environment. Stop and restart around each navigation, retaining and merging the entries afterward.
- Dynamically created scripts are missing: Set
reportAnonymousScripts: trueif you need scripts without associated URLs, includingevalandnew Functionscripts. - Downstream tooling needs more detail: Consider
includeRawScriptCoverage: trueif it requires raw V8 entries; it is off by default. - The byte percentage is undefined: A run with no collected script text gives a zero denominator. Guard the calculation and check that collection was started before the intended page activity.
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ScreenshotNeo is a website screenshot API, not a JavaScript coverage collector; it does not replace Puppeteer’s coverage API or produce Istanbul reports. If your adjacent task is capturing a page image or PDF, one GET request can do that without setting up a browser:
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