`app.decorateRequest()`

Adds a property or method to every request object.

Since Fastify 5 Spec ↗

Syntax

app.decorateRequest(name, value)

Parameters

Name	Type	Required	Description
`name`	`string`	No	The property name added to FastifyRequest.
`value`	`any`	No	A default value, getter, or null placeholder for per-request data.

Returns

FastifyInstance — The instance, for chaining.

Examples

import Fastify from 'fastify';

const app = Fastify();

app.decorateRequest('user', null);

declare module 'fastify' {
  interface FastifyRequest {
    user: { id: string } | null;
  }
}

app.addHook('preHandler', async (req) => {
  req.user = { id: 'u_1' };
});

Notes

Decorate with a primitive or null placeholder rather than an object literal so each request gets its own value. Populate the field in a hook such as preHandler.