composition.js

const users = {
  1: { name: 'bob' },
  2: { name: 'sally' }
}

const posts = [
  { author: 'sally', title: 'Hello World' },
  { author: 'bob', title: 'How to do stuff' }
]

const getUserName = sequentialCallback(
  (id, callback) => callback(null, users[id]),
  (user, callback) => callback(null, user.name)
)

const getUserPosts = sequentialCallback(
  getUserName,
  (name, callback) => callback(null, posts.filter((p) => p.author === name))
)

getUserPosts(2, (err, posts) => {
  console.log(posts)
})