code-coverage.js

const puppeteer = require('puppeteer');

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

  // Gather coverage for JS and CSS files
  await Promise.all([page.coverage.startJSCoverage(), page.coverage.startCSSCoverage()]);

  await page.goto('https://pptr.dev');

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

  // Calculates # bytes being used based on the coverage
  const calculateUsedBytes = (type, coverage) =>
    coverage.map(({url, ranges, text}) => {
      let usedBytes = 0;

      ranges.forEach((range) => (usedBytes += range.end - range.start - 1));

      return {
        url,
        type,
        usedBytes,
        totalBytes: text.length,
        percentUsed: `${(usedBytes / text.length * 100).toFixed(2)}%`
      };
    });

  console.info([
    ...calculateUsedBytes('js', jsCoverage),
    ...calculateUsedBytes('css', cssCoverage),
  ]);

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