Fastify: How to call a decorate methods in typescript

[Jegannathan]

[cemremengu]

I think you should be able to call them like you do in JavaScript. Could you please elaborate a little?

[Jegannathan]

fastify.decorate('config',{
port:4000
})

in js fastify.config.port is possible

But in typescript fastify.config.port throw an error like property config is not present in Fastify instance

[tuelsch]

You will need to augment the fastify type definition, so typescript knows about the new property:

File: yourproject/@types/fastify/index.d.ts (if the compiler does not pick up your definitions file, add the location of the @types folder to typeRoots in your tsconfig.json)

import fastify from 'fastify';

declare module 'fastify' {
  export interface FastifyInstance<
    HttpServer = Server,
    HttpRequest = IncomingMessage,
    HttpResponse = ServerResponse,
  > {
    port: number;
  }
}

Read more about augmentation in the docs: https://www.typescriptlang.org/docs/handbook/declaration-merging.html#module-augmentation

A blog explaining the process in more detail: https://medium.com/car2godevs/fastify-with-typescript-production-ready-integration-2303318ecd9e