Getting Started with Server-Side Development with Fastify

Fastify is a small Node framework for developing back end web apps.

In this article, we’ll look at how to create back end apps with Fastify.

Installation

We install the fastify package by running:

npm i fastify --save

with NPM or:

yarn add fastify

with Yarn.

First App

We create a simple server app with a few lines of code.

For example, we can write:

const fastify = require('fastify')({
  logger: true
})

fastify.get('/', (request, reply) => {
  reply.send({ hello: 'world' })
})

fastify.listen(3000, '0.0.0.0', (err, address) => {
  if (err) {
    fastify.log.error(err)
    process.exit(1)
  }
  fastify.log.info(`server listening on ${address}`)
})

to create a simple server with the / route.

logger set to true enables the built-in logger.

reply.send sends a response.

fastify.listen starts the app and listens to the server.

The first argument is the port, the 2nd argument is the IP address to listen for requests from. '0.0.0.0' listens to all addresses.

When we go to / , we see:

{"hello":"world"}

returned.

We can also use astbc and await in our router handlers.

For example, we can write:

const fastify = require('fastify')({
  logger: true
})

fastify.get('/', async (request, reply) => {
  return { hello: 'world' }
})

const start = async () => {
  try {
    await fastify.listen(3000, '0.0.0.0')
  } catch (err) {
    fastify.log.error(err)
    process.exit(1)
  }
}
start()

We just return the object we want as the response.

And we call fastify.listen without the callback.

Validate Request Data

We can validate request data by passing in an option to our route.

For example, we can write:

const fastify = require('fastify')({
  logger: true
})

const opts = {
  schema: {
    body: {
      type: 'object',
      properties: {
        foo: { type: 'string' },
        bar: { type: 'number' }
      }
    }
  }
}

fastify.post('/', opts, async (request, reply) => {
  return { hello: 'world' }
})

const start = async () => {
  try {
    await fastify.listen(3000, '0.0.0.0')
  } catch (err) {
    fastify.log.error(err)
    process.exit(1)
  }
}
start()

to create our schema and then pass in the properties into it.

We specify the types of the foo and bar properties.

This lets us specify the properties that are accepted.

Serializing Data

We can also specify the schema for the response.

For example, we can write:

const fastify = require('fastify')({
  logger: true
})

const opts = {
  schema: {
    response: {
      200: {
        type: 'object',
        properties: {
          hello: { type: 'string' }
        }
      }
    }
  }
}

fastify.post('/', opts, async (request, reply) => {
  return { hello: 'world' }
})

const start = async () => {
  try {
    await fastify.listen(3000, '0.0.0.0')
  } catch (err) {
    fastify.log.error(err)
    process.exit(1)
  }
}
start()

to specify the response that’s returned by the / route.

Run Our Server

We can run our Fastify app with the Fastify CLI.

We install it by running:

npm i fastify-cli

Then in package.json , we add:

{
  "scripts": {
    "start": "fastify start server.js"
  }
}

Then we run it with:

npm start

Conclusion

We can create a simple back end Node web app easily with Fastify.