Create a minimal REST API in NodeJS with Fastify

Before diving into creating our first API with Fastify, you'll need to make sure you're using a version of NodeJS equal to or greater than 20.0.0!

You can check the current version with node —version

Project setup

If everything is in order, we can start initializing our project. Start by creating a my-first-api folder, and inside this folder, run the following commands:

$> npm init
$> npm install fastify

Then open the package.json file, and add the following line:

"type": "module"

This has nothing to do with Fastify specifically

But declaring our project as a module will enable import, which is a more modern equivalent of require.

For example, we'll write:

import Fastify from 'fastify';

// instead of

const Fastify = require('fastify');

A minimal API

Create an app.js file in your project folder, and copy-paste the following code inside it:

// We import the framework
import Fastify from 'fastify'

// We initialize it with options
const fastify = Fastify({
  logger: true
})

// We declare our first route
fastify.get('/', async function handler (request, reply) {
  return { hello: 'world' }
});

// And we start the server!
try {
  await fastify.listen({ port: 3000 })
} catch (err) {
  fastify.log.error(err)
  process.exit(1)
}

Try running your api with node index.js and you should see this in your console:

Server listening at http://[::1]:3000

Try accessing your API's first route by following this link: http://localhost:3000

If your browser responds with {"hello":"world"} then your API is up and running!