fastify-express VS ajv

As mentioned in part 2 of this series, using the @fastify/express plugin is the quickest way to get your existing Express application working with Fastify. The plugin adds full Express compatibility to Fastify so that you can easily use any Express middleware — or even an entire Express application — with your Fastify instance, and it will just work with no changes required.

Fastify also supports Express-style middleware but it requires you to install an external plugin such as @fastify/express or @fastify/middie. This eases migration from Express to Fastify, but it should not be used in greenfield projects in favor of hooks. Note that in many cases, you can find a native Fastify plugin that provides the same functionality as Express middleware.

Fastify Express

It's correct that fastify doesn't support middleware out of the box. But Nestjs and its fastify adapter support it. I think they are using this package: https://github.com/fastify/fastify-express

I've found that the fastify-express plugin makes migrating from Express to Fastify much easier: https://github.com/fastify/fastify-express. It has full support for Express middleware and routes, allowing you to migrate things in stages if you prefer.

An excellent alternative to Express or Restify is the Fastify framework. It has full native support for async code and is in active development. There is also a fastify-express plugin available which can help ease your migration path away from Express.

It seems like most of the important plugins have been built and available in the fastify ecosystem. Also with https://github.com/fastify/fastify-express you can use all the express middleware, and actually wrap your entire express application in fastify (obviously just cause you can, not cause you should)

This framework is well maintained, and provides an official compatibility layer for Express to help you migrate your application.

Ajv’s documentation is available here.

In the JavaScript ecosystem you can use the excellent AJV package to validate any JavaScript object against a JSON schema. This is especially useful to ensure that API contracts are maintained when communicating with other services.

Since Fastify supports schema validation with Ajv, the validate module is no longer required on the /shorten route, and we can specify the JSON schema directly on the route. The controllers for both routes will largely remain the same, except that the res parameter is renamed to reply as before:

There's a ton of schema validators out there and most devs have their personal favorite. Mine was zod and is now typebox + ajv.

Good validator library: https://www.npmjs.com/package/ajv

Fastify uses JSON schema to define the validation rules for each route's input payload, which includes the request body, query string, parameters, and headers. The JSON schema is a standard format for defining the structure and constraints of JSON data, and Fastify uses Ajv, one of the fastest and most efficient JSON schema validators available.

In Fastify, JSON schema validation is a built-in feature that allows you to validate the payload of incoming requests before the handler function is executed. This ensures that incoming data is in the expected format and meets the required criteria for your business logic. Fastify's JSON schema validation is powered by the Ajv library, a fast and efficient JSON schema validator.

I think you're looking for a json schema validator like Ajv or Zod.

We can use JSON Schema to validate that our data adheres to a specific structure. Ajv is one popular validator tool for JavaScript applications that allows us to create a schema and then validate JSON against that schema. Here's an example of using Ajv to validate one of the above JSON examples against a schema:

Hey HN,

We're designing a new system and have been kicking the can about JSON object definitions and validation. Soon we need to settle on a system to validate API request bodies and provide helpful error messages.

In the past, I've used JSON Schema ( https://json-schema.org/ ) to define definitions and ajv ( https://ajv.js.org/ ) to validate, but it's a bit verbose and ajv validation errors are more cryptic than I'd like to deal with.

TypeSchema looks interesting. It seems solid (and perhaps stable?), but development hasn't been active for 2 years. It also looks like we'd still need to generate JSON Schema and choose a validation library

Anyway, I'm very curious how others are approaching this problem. How do you organize and generate validations for your type definitions? What libraries do you use to validate and provide human readable error messages?

Thank you!