This is the index.js file of Hello world GraphQL project.

index.js

const express = require('express');
const { ApolloServer, gql } = require('apollo-server-express');

// This is the schema types
const typeDefs = gql`
  type Query {
    hello: String
  }
`;

// This is the resolver methods
const resolvers = {
  Query: {
    hello: () => 'Hello world!',
  },
};
const server = new ApolloServer({ typeDefs, resolvers });

const app = express();
server.applyMiddleware({ app });

app.listen({ port: 4000 }, () =>
  console.log(` Server started at http://localhost:4000${server.graphqlPath}`)
);