resolvers.js

const resolvers = {
  Query: {
    movies: () => movies,
    movie: (_, { id }) => movies.find(movie => movie.id == id)
  },
  Mutation: {
    addMovie: (_, { title, year }) => {
      const newMovie = {
        title,
        year,
        id: randomId(10)
      }
      movies.push(newMovie)

      return newMovie
    }
  }
};