graphql-server.js

const express = require('express')
const cors = require('cors')
const { graphqlHTTP } = require('express-graphql')
const { buildSchema } = require('graphql') // GraphQL schema
var schema = buildSchema(`
    type Query {
        course(id: Int!): Course
        courses(topic: String): [Course]
    }

    type Mutation {
      updateCourseTopic(id: Int!, topic: String!): Course
    }

    type Course {
      id: Int
      title: String
      author: String
      description: String
      topic: String
      url: String
    }
`)

const coursesData = [
  {
    id: 1,
    title: 'The Complete Node.js Developer Course',
    author: 'Andrew Mead, Rob Percival',
    description:
      'Learn Node.js by building real-world applications with Node, Express, MongoDB, Mocha, and more!',
    topic: 'Node.js',
    url: 'https://codingthesmartway.com/courses/nodejs/',
  },
  {
    id: 2,
    title: 'Node.js, Express & MongoDB Dev to Deployment',
    author: 'Brad Traversy',
    description:
      'Learn by example building & deploying real-world Node.js applications from absolute scratch',
    topic: 'Node.js',
    url: 'https://codingthesmartway.com/courses/nodejs-express-mongodb/',
  },
  {
    id: 3,
    title: 'JavaScript: Understanding The Weird Parts',
    author: 'Anthony Alicea',
    description:
      'An advanced JavaScript course for everyone! Scope, closures, prototypes, this, build your own framework, and more.',
    topic: 'JavaScript',
    url: 'https://codingthesmartway.com/courses/understand-javascript/',
  },
]

const getCourse = function (args) {
  var id = args.id
  return coursesData.filter(course => {
    return course.id == id
  })[0]
}

const getCourses = function (args) {
  if (args.topic) {
    var topic = args.topic
    return coursesData.filter(course => course.topic === topic)
  } else {
    return coursesData
  }
}

const updateCourseTopic = function ({ id, topic }) {
  coursesData.map(course => {
    if (course.id === id) {
      course.topic = topic
      return course
    }
  })
  return coursesData.filter(course => course.id === id)[0]
}

const root = {
  course: getCourse,
  courses: getCourses,
  updateCourseTopic,
}

const app = express()
app.use(cors())
app.use(
  '/graphql',
  graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true,
  }),
)

app.listen(4000, () =>
  console.log('Express GraphQL Server Now Running On localhost:4000/graphql'),
)