teaser.js

await (async () => {
  try {
    const userRes = await fetch(`/api/loggedInUser`);
    const user = await userRes.json();

    if (!user?.id) {
      throw new Error(`No user id found`);
    }

    const responses = await Promise.all([
      fetch(`/api/user/${user.id}/comments`),
      fetch(`/api/user/${user.id}/books`),
    ]);

    const [comments, books] = await Promise.all(
      responses.map((res) => res.json())
    );
    console.log(books, comments);
  } catch (error) {
    console.error(error);
  }
})();
})();