graphql-parse-fields.js

const { ApolloServer, gql } = require('apollo-server');
const parseFields = require('graphql-parse-fields');

const typeDefs = gql`
  type User {
    firstName: String
    lastName: String
    age: Int
  }

  type Query {
    users: [User]
  }
`;

const users = [
  { firstName: 'John', lastName: 'Doe', age: 33 },
  { firstName: 'Jane', lastName: 'Doe', age: 33 }
];

const getUsers = requiredFields => {
  return users.map(user => pick(user, requiredFields));
};

const resolvers = {
  Query: {
    users: (parent, args, context, info) => {
      const requiredFields = Object.keys(parseFields(info));
      const users = getUsers(requiredFields);
      console.log(users);
      return users;
    }
  }
};

const server = new ApolloServer({
  typeDefs,
  resolvers
});

const pick = (obj, keys) => {
  return keys
    .map(k => (k in obj ? { [k]: obj[k] } : {}))
    .reduce((res, o) => Object.assign(res, o), {});
};

server.listen(7000).then(({ url }) => {
  console.log(`Server running at ${url}`);
});