Servidor básico con lo mínimo en GraphQL haciendo uso de GraphiQL

index.js

const express = require("express");
const { buildSchema } = require("graphql");
const { graphqlHTTP } = require("express-graphql");
const bodyParser = require('body-parser');
const courses = [
  {
    id: 1,
    title: "GraphQL de 0 a experto",
    views: 29290,
  },
  {
    id: 2,
    title: "Tienda de videojuegos - MEAN+G",
    views: 122,
  },
];

const schema = buildSchema(`
    type Course {
        id: ID!
        title: String!
        views: Int
    }
    type Query {
        getCourses: [Course]
    }
`);

// The root provides a resolver function for each API endpoint
var root = {
    getCourses: () => {
        return courses;
    }
};

const app = express();
// parse application/json
app.use(bodyParser.json())
app.use('/graphql', graphqlHTTP({
    schema,
    graphiql: true,
    rootValue: root
}));

app.listen(4000, () => {
    console.log('Server ok in http://localhost:4000/graphql');
})

package.json

{
  "name": "graphql-basic",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "start": "npx nodemon index.js"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "body-parser": "^1.19.0",
    "express": "^4.17.1",
    "express-graphql": "^0.11.0",
    "graphql": "^15.3.0"
  },
  "devDependencies": {
    "nodemon": "^2.0.4"
  }
}