Define Resolver for Object within Object

Author field in the Book object needs a self defined resolver to access the fields in Author object.

type Author {
  name: String!
  id: ID!
  born: Int
  bookCount: Int
}
type Book {
  title: String!
  published: Int!
  author: Author!
  id: ID!
  genres: [String!]!
}
const resolvers = {
  Query: {
  // ...
  },
  Book: {
    author: (root) => {
      return {
        name: root.author.name,
        id: root.author.id,
        born: root.author.born
      }
    }
  }
}