Server-Side Development with Fastify — Response Serialization and Request Validation Error Handling

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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.

Serialization

We can change the way that responses are serialized.

To do this, we write:

const fastify = require('fastify')({})
const schema = {
  response: {
    '2xx': {
      type: 'object',
      properties: {
        value: { type: 'string' },
        otherValue: { type: 'boolean' }
      }
    },
    201: {
      value: { type: 'string' }
    }
  }
}
fastify.get('/', { schema }, (request, reply) => {
  reply.send({ value: 1, otherValue: 'foo' })
})
const start = async () => {
  try {
    await fastify.listen(3000, '0.0.0.0')
  } catch (err) {
    fastify.log.error(err)
    process.exit(1)
  }
}
start()

We add the response schema with the schema.response property.

We specify the response data type and structure for each status code.

The type specifies the data type of the response.