Learn FASTIFY with Real Code Examples

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

let count = 0

fastify.get('/counter', async (request, reply) => {
    return { count }
})

fastify.post('/counter/increment', async (request, reply) => {
    count++
    return { count }
})

fastify.post('/counter/decrement', async (request, reply) => {
    count--
    return { count }
})

fastify.post('/counter/reset', async (request, reply) => {
    count = 0
    return { count }
})

const start = async () => {
    try {
        await fastify.listen({ port: 3000 })
        console.log('Fastify server running on http://localhost:3000')
    } catch (err) {
        fastify.log.error(err)
        process.exit(1)
    }
}
start()

Demonstrates a simple Fastify REST API with a counter using routes and state management.

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

fastify.get('/greet', async (request, reply) => {
    const name = request.query.name || 'Guest'
    return `Hello, ${name}!`
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Handle query parameters in GET requests.

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

fastify.get('/user/:id', async (request, reply) => {
    const userId = request.params.id
    return `User ID: ${userId}`
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Handle dynamic URL parameters in Fastify routes.

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

fastify.register(require('@fastify/formbody'))

fastify.post('/echo', async (request, reply) => {
    return { received: request.body }
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Parse JSON body data in POST requests.

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

fastify.addHook('preHandler', async (request, reply) => {
    console.log(`${request.method} ${request.url}`)
})

fastify.get('/', async (request, reply) => {
    return 'Middleware example'
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Custom preHandler middleware logging requests.

const fastify = require('fastify')({ logger: true })
fastify.register(require('@fastify/static'), { root: __dirname + '/public' })

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Serve static files using Fastify.

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

const plugin = async (instance, options) => {
    instance.get('/hello', async (request, reply) => {
        return 'Hello from plugin'
    })
}

fastify.register(plugin, { prefix: '/api' })

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Organize routes using Fastify plugin.

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

fastify.get('/error', async (request, reply) => {
    throw new Error('Something went wrong')
})

fastify.setErrorHandler(async (error, request, reply) => {
    console.error(error.message)
    reply.status(500).send('Server Error')
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Custom error handling in Fastify.

const fastify = require('fastify')({ logger: true })
fastify.register(require('@fastify/cors'))

fastify.get('/', async (request, reply) => {
    return 'CORS enabled'
})

fastify.listen({ port: 3000 }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Enable CORS for all routes.

require('dotenv').config()
const fastify = require('fastify')({ logger: true })
const port = process.env.PORT || 3000

fastify.get('/', async (request, reply) => {
    return `Server running on port ${port}`
})

fastify.listen({ port }, (err, address) => {
    if (err) throw err
    console.log(`Server running at ${address}`)
})

Access environment variables in Fastify.