puppeteer/test/assets/networkidle.html

<script>
  async function sleep(delay) {
    return new Promise(resolve => setTimeout(resolve, delay));
  }

  async function main() {
    const roundOne = Promise.all([
      fetch('fetch-request-a.js'),
      fetch('fetch-request-b.js'),
      fetch('fetch-request-c.js'),
    ]);

    await roundOne;
    await sleep(50);
    await fetch('fetch-request-d.js');
  }

  main();
</script>