server.js

var express = require('express');
var express_graphql = require('express-graphql');
var { buildSchema } = require('graphql');
// GraphQL schema
var schema = buildSchema(`
  type Query {
    movie(id: Int!): Movie
    movies(rate: String): [Movie]
  },
  type Movie {
    id: Int
    title: String
    rate: String
    year: Int
}
`);

var MoviesList = [
  {
    id: 1,
    title: 'Avengers: Endgame',
    rate: '8.7',
    Year: 2019
  },
  {
    id: 2,
    title: 'John Wick: Chapter 3 - Parabellum',
    rate: '7.9',
    year: 2019
  },
  {
    id: 3,
    title: 'Once Upon a Time ... in Hollywood',
    rate: '8.5',
    year: 2019
  },
  {
    id: 4,
    title: 'Jurassic World: Fallen Kingdom',
    rate: '6.5',
    year: 2018
  }
]

var getMovie = function(args) { 
  var id = args.id;
  return MoviesList.filter(movie => {
      return movie.id == id;
  })[0];
}

var getMovies = function(args) {
  if (args.rate) {
    var rate = args.rate;
    return MoviesList.filter(movie => movie.rate === rate);
  } else {
    return MoviesList;
  }
}
var root = {
  movie: getMovie,
  movies: getMovies
};
// Create an express server and a GraphQL endpoint
var app = express();
app.use('/graphql', express_graphql({
  schema: schema,
  rootValue: root,
  graphiql: true
}));
app.listen(4000, () => console.log('Express GraphQL Server Now Running On localhost:4000/graphql'));