blog-async-await-chained-promises.js

function addComment(comment) {
  return fetchPostBySlug(comment.postSlug)
    .then((post) => {
      if (!post.isCommentingEnabled) {
        return Promise.reject(new Error('Commenting is disabled.'));
      }

      return isUserAllowedToComment(post, comment.user)
        .then((isAllowed) => ({ isAllowed, post }));
    }).then((input) => {
      if (!input.isAllowed) {
        return Promise.reject(
          new Error('The user is not allowed to comment on this post.')
        );
      }

      return insertComment(input.post.id, comment.user, comment.message);
    }).then((result) => {
      return result.record;
    });
}