[Fixed] Typescript Declaration Merging Express Request Object and Passport.js User/Session

Issue

I am using passportjs middleware for authentication in an express/nodejs application. I am getting errors about properties on my request.user object despite having followed the steps for Declaration Merging.

I have created a file at /types/index.d.ts in my project root, and added the following to my tsconfig.json

"typeRoots": [
  "/types/index.ts", "node_modules/@types"
]

My global declaration merge looks like this:

import { User } from "../users/user.interface";
declare global {
  namespace Express {
    export interface Request {
        user: User;
    }
  }
}

** UPDATE **
I have gotten the req.user object to stop throwing errors by changing my Declaration Merge to a Module Augmentation like so:

import { User } from "../users/user.interface";

declare module "express-serve-static-core" {
    interface Request {
        user: User;
    }
}

When referencing request.session object I get the following error: Property 'session' does not exist on type 'Request<ParamsDictionary, any, any, ParsedQs, Record<string, any>>'.

Shouldn’t passport’s @types/passport types be merging with express’s request object to add a session?

Does anyone know how I can successfully squash these errors / get TS to recognize this Declaration Merge. I’m new to typescript and have been able to solve most of the issues I have come across but this one just keeps on surfacing.

Solution

To extend the User type used by Passport, you would merge your declarations into global.Express.User:

declare global {
  namespace Express {
    interface User {
        /* declare your properties here */
    }
  }
}

The type definitions provided by @types/passport do not define global.Express.Request#session, that is defined by @types/express-session here.