GraphQL JavaScript Library (Node.js): Complete Guide to Apollo Server and Tools

GraphQL Library for Node.js: Apollo Server and Development Tools

GraphQL is a query language for APIs that allows clients to request only the data they need. For development on Node.js, the most popular library is Apollo Server. It provides a complete set of tools for creating, testing, and deploying GraphQL APIs. In this article, we will thoroughly examine key components, approaches, and code examples.

What is Apollo Server?

Apollo Server is an open-source library that allows you to quickly create a GraphQL server on Node.js. It supports multiple transports (HTTP, WebSocket) and easily integrates with frameworks (Express, Koa, Fastify). Key features:

• Automatic documentation generation via GraphQL Playground.
• Support for subscriptions via WebSocket.
• Caching and data batching mechanism (data loaders).
• Flexible middleware system for authentication and authorization.

Installation and Basic Setup

To get started, install the apollo-server and graphql packages:

npm install apollo-server graphql

Create a simple server that returns a greeting:

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

// Define the schema (SDL)const typeDefs = gql`  type Query {    hello: String  }`;

// Resolvers — functions that return dataconst resolvers = {  Query: {    hello: () => 'Hello, GraphQL!',  },};

// Start the serverconst server = new ApolloServer({ typeDefs, resolvers });server.listen().then(({ url }) => {  console.log(`🚀 Server running at ${url}`);});

Data Types and Schemas

In GraphQL, the schema defines all available types and operations. Basic types:

• String, Int, Float, Boolean, ID — scalar types.
• [Type] — list of objects.
• type — custom object.
• input — type for mutation input parameters.

Example schema for a blog:

type User {  id: ID!  name: String!  posts: [Post!]!}

type Post {  id: ID!  title: String!  content: String!  author: User!}

type Query {  user(id: ID!): User  posts(limit: Int): [Post!]!}

type Mutation {  createUser(name: String!): User!}

Resolvers: Connecting Schema to Data

Each schema field must have a corresponding resolver. Resolvers can retrieve data from a database (MongoDB, PostgreSQL), external APIs, or static arrays.

const users = [  { id: '1', name: 'Anna' },  { id: '2', name: 'Boris' },];

const posts = [  { id: '10', title: 'GraphQL for Beginners', content: '...', authorId: '1' },  { id: '20', title: 'Node.js Tips', content: '...', authorId: '2' },];

const resolvers = {  Query: {    user: (_, { id }) => users.find(u => u.id === id),    posts: (_, { limit }) => limit ? posts.slice(0, limit) : posts,  },  Mutation: {    createUser: (_, { name }) => {      const newUser = { id: String(users.length + 1), name };      users.push(newUser);      return newUser;    },  },  User: {    posts: (parent) => posts.filter(p => p.authorId === parent.id),  },};

Code-first Approach with TypeGraphQL

For large projects, it is more convenient to use the code-first approach, where the schema is generated from TypeScript classes. The type-graphql library allows you to write code that is both a type and a resolver.

npm install type-graphql reflect-metadata class-validator

Example entity class:

import { ObjectType, Field,