How to use promise to avoid callback hell? [duplicate]

Answer 1

You are nesting the callbacks. You don't need to do this. If you return a promise from .then then any .then you chain to it will be resolved when that promise gets resolved:

promise.then(post => Comments.find({id: post.id})
  .then(comments => Links.find({id: post.id})
  .then(links => {});

The comments query does not depend on links so you can actually do both queries at once:

promise.then(post => {
  return Promise.all([
     post,
     Comments.find({id: post.id}),
     Links.find({id: post.id}),
  ]);
}).then(data => res.json({
  post: data[0],
  comments: data[1],
  links: data[2],
});

If you use a library like bluebird you can also use something like the spread operator to make the names more transparent.

---

I would also look into using co for generator-based control flow as I think this is even clearer:

co(function* () {
  const post = yield Posts.findOne({id});
  const [comments, links] = yield [
    Comments.find({id: post.id}),
    Links.find({id: post.id}),
  ];

  res.json({post, comments, links});
});