Fastify Basics

Node.js · Reference cheat sheet

📋 Overview

Fastify is a high-performance Node web framework focused on schemas, plugins, and low overhead. Validation and serialization are first-class via JSON Schema.

🔧 Core concepts

API	Role
`Fastify()`	Create instance
`fastify.route` / `.get`	Register routes
`schema`	Validate request + serialize response
`reply`	Response object (`send`, `code`)
`listen`	Bind host/port

Hook (examples)	When
`onRequest`	Early request
`preHandler`	Before handler
`onSend`	Before payload sent
`onError`	Error path

💡 Examples

Minimal server:

import Fastify from "fastify";

const app = Fastify({ logger: true });
app.get("/", async () => ({ ok: true }));
await app.listen({ port: 9000, host: "0.0.0.0" });

Schema validation:

app.post(
  "/users",
  {
    schema: {
      body: {
        type: "object",
        required: ["email"],
        properties: { email: { type: "string", format: "email" } },
      },
    },
  },
  async (req, reply) => {
    reply.code(201);
    return req.body;
  },
);

Async handler errors:

app.get("/boom", async () => {
  throw Object.assign(new Error("nope"), { statusCode: 400 });
});

⚠️ Pitfalls

Prefer async handlers or call reply.send — don't mix both carelessly.
Validation errors return 400 by default; customize with setErrorHandler.
Plugin encapsulation means decorations are not always global — register shared plugins at the right scope.

Fastify Basics

Fastify Basics

📋 Overview

🔧 Core concepts

💡 Examples

⚠️ Pitfalls

🔗 Related

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