error-translation-for-the-win.js

const databaseGetUser = id =>
  id === 'not-exists'
    ? Promise.reject('some weird database error')
    : Promise.resolve({id, username: 'username'})

const databaseGetPosts = user =>
  user.id === 'fail-to-get-posts'
    ? Promise.reject('some weird database error for posts')
    : Promise.resolve([{title: 'A'}, {title: 'B'}])

async function getUserWithPosts(id) {
  const user = await databaseGetUser(id).catch(err => { throw `user ${id} doesn't exists ` })
  const posts = await databaseGetPosts(user).catch(err => { throw 'failed to load posts' })
  return {user, posts}
}

getUserWithPosts('lubien').then(console.log)               // works fine
getUserWithPosts('not-exists').catch(console.error)        // 'user not-exists doesn't exists'
getUserWithPosts('fail-to-get-posts').catch(console.error) // 'failed to load posts'