Type-Safe Fastify

Welcome to the final chapter of this book! This chapter will explore how Fastify’s built-in TypeScript support can help us write more robust and maintainable applications.

Type safety is a crucial aspect of modern software development. It allows developers to catch errors and bugs early in the development process, reducing the time and cost of debugging and testing. By using TypeScript with Fastify, you can benefit from compile-time type safety and avoid unexpected runtime errors, leading to more stable and reliable applications.

Using TypeScript with Fastify can also improve the developer experience by providing better code completion, type inference, and documentation. In addition, Fastify has first-class support for TypeScript, providing everything needed to build robust and scalable applications, including interfaces and generics.

Moreover, using TypeScript can make deployments safer by catching potential errors and bugs before they go live. It...

Technical requirements

To follow along with this chapter, you will need the following:

• A working Node.js 18 installation (https://nodejs.org/)
• The VS Code IDE (https://code.visualstudio.com/)
• A Git repository is recommended but not mandatory (https://git-scm.com/)
• A terminal application

The code for the project can be found on GitHub at https://github.com/PacktPublishing/Accelerating-Server-Side-Development-with-Fastify/tree/main/Chapter%2015.

In the next section, we’ll dive into the details of setting up the Fastify project in TypeScript, adding all of the dependencies we need to make it work.

Creating the project

Creating a new Fastify project with TypeScript support is straightforward but requires adding some extra dependencies. In this section, we’ll look at the process of manually setting up a new Fastify project with TypeScript and installing the necessary dependencies.

Let’s start with the package.json file, a configuration file for a Node.js project. It includes information about the dependencies, the entry point, and scripts. The following is just a partial snippet since we will evolve it through the sections of this chapter:

{
  "version": "1.0.0",
  "main": "dist/server.js", // [1]
  "dependencies": {
    "@fastify/autoload": "^5.7.1",
    "fastify": "^4.15.0"
  },
  "devDependencies": {
    "@types/node": "^18.15.11"...

Using Fastify type-providers

A Fastify type-provider is a TypeScript-only package that simplifies the definition of JSON schemas by providing type annotations and generics. Using it will allow Fastify to infer type information directly from schema definitions. Type-providers enable developers to define API endpoints’ expected input and output data easily, automatically check the type correctness at compile time, and validate the data at runtime.

Fastify supports several type-providers, such as json-schema-to-ts and TypeBox. In TypeScript projects, using a type-provider can help reduce the boilerplate code required for input validation and reduce the likelihood of bugs due to invalid data types. This can ultimately make your code more robust, maintainable, and scalable.

For the sake of brevity, in the following example, we will focus only on the TypeBox type-provider. However, since which type-provider you use is based on personal preference, we encourage you to try other...

Generating the API documentation

The OpenAPI specification is a widely adopted and open standard for documenting RESTful APIs. It provides a format for describing the structure and operations of an API in a machine-readable format, allowing developers to understand and interact with the API quickly.

The specification defines a set of JSON or YAML files that describe an API’s endpoints, parameters, responses, and other details. This information can be used to generate API documentation, client libraries, and other tools that make it easier to work with the API.

Swagger and OpenAPI specifications

Swagger and OpenAPI are two related specifications, with OpenAPI being the newer version of Swagger. Swagger was originally an open source project, but later, the specification was acquired by SmartBear and renamed to OpenAPI. Today, the OpenAPI initiative, a consortium of industry leaders, maintains the specification. Swagger is also known as OpenAPI v2, while only OpenAPI generally...

Summary

In this chapter, we learned why type safety is crucial in modern software development and how using TypeScript with Fastify can help catch errors and bugs early in development. The chapter also covered how using TypeScript with Fastify can improve the developer experience by providing better code completion, type inference, and the ability to auto-generate the documentation site for our APIs.

Congratulations on reaching the final chapter of this book! Throughout this journey, we have learned about the Fastify web framework and how it can help us build high-performance web applications.