index.js

const express = require('express');
const {graphqlHTTP} = require('express-graphql');
const {buildSchema, subscribe} = require('graphql');
const {PubSub} = require('graphql-subscriptions');
const { createServer } = require('http');
const { useServer } = require('graphql-ws/use/ws');
const { WebSocketServer } = require('ws');

// Schema
const schema = buildSchema(`
    type Query {
        user: [User]
        userById(id:Int!): User
    }

    type Mutation {
        userChangeName(id:Int!, name:String!): User
    }

    type Subscription {
      updatedList: [User]
    }
        
    type User {
        id: Int
        name: String
    }`);

const users = [
  { id: 23, name: "Jason" },
  { id: 25, name: "Delfie" },
  { id: 1,  name: "Caleb" }
];

const pubSub = new PubSub();

const root = {
  user: () => users,
  userById: (args) => users.find(u => u.id === args.id),
  userChangeName: async (args) => {
    for (let i = 0; i < users.length; i++) {
      if (users[i].id == args.id) {
        users[i].name = args.name
        setTimeout(() => {
          pubSub.publish('OPERATION_FINISHED', { updatedList: [...users] });
        }, 1000);
        return users[i]
      }
    }
    return null
  },
  updatedList: {
    subscribe: () => pubSub.asyncIterableIterator(['OPERATION_FINISHED'])
  }
};

const app = express();
app.use('/helloGraph', graphqlHTTP({
  schema,
  rootValue: root,
  graphiql: { subscriptionEndpoint: 'ws://localhost:4000/helloGraph' }
}));

const server = createServer(app);

const wsServer = new WebSocketServer({
  server,
  path: '/helloGraph',
});
useServer({ schema, roots: { subscription: root } }, wsServer);

server.listen(4000, () => console.log("Listening on port 4000 for GraphQL"))