blog-async-await-waterfall.js

async function addComment(comment) {
  const post = await fetchPostBySlug(comment.postSlug);

  if (!post.isCommentingEnabled) {
    throw new Error('Commenting is disabled.');
  }

  const isAllowed = await isUserAllowedToComment(post, comment.user);

  if (!isAllowed) {
    throw new Error('The user is not allowed to comment on this post.');
  }

  const result = await insertComment(post.id, comment.user, comment.message);

  return result.record;
}