Chrome Devtools Coverage: how to save or capture code used code?

You can do this with puppeteer

(async () => {
  const browser = await puppeteer.launch();
  const page = await browser.newPage()

  //Start sending raw DevTools Protocol commands are sent using `client.send()`
  //First off enable the necessary "Domains" for the DevTools commands we care about
  const client = await page.target().createCDPSession()
  await client.send('Page.enable')
  await client.send('DOM.enable')
  await client.send('CSS.enable')

  const inlineStylesheetIndex = new Set();
  client.on('CSS.styleSheetAdded', stylesheet => {
    const { header } = stylesheet
    if (header.isInline || header.sourceURL === '' || header.sourceURL.startsWith('blob:')) {
      inlineStylesheetIndex.add(header.styleSheetId);
    }
  });

  //Start tracking CSS coverage
  await client.send('CSS.startRuleUsageTracking')

  await page.goto(`http://localhost`)
  // const content = await page.content();
  // console.log(content);

  const rules = await client.send('CSS.takeCoverageDelta')
  const usedRules = rules.coverage.filter(rule => {
    return rule.used
  })

  const slices = [];
  for (const usedRule of usedRules) {
    // console.log(usedRule.styleSheetId)
    if (inlineStylesheetIndex.has(usedRule.styleSheetId)) {
      continue;
    }

    const stylesheet = await client.send('CSS.getStyleSheetText', {
      styleSheetId: usedRule.styleSheetId
    });

    slices.push(stylesheet.text.slice(usedRule.startOffset, usedRule.endOffset));
  }

  console.log(slices.join(''));

  await page.close();
  await browser.close();
})();