增强外部 TypeScript 模块

Question

I'm currently studying how to augment external modules in TypeScript, reading the official docs and the DefinitelyTyped guides, checking examples and so on. My objective right now is to add custom properties to the express.Request interface (eg a user that implements a given User interface.

Like the following:

// types/express/index.d.ts

declare namespace Express {
  export interface Request {
    user: types.User;
  }
}

The User interface is declared in a separate declaration file:

// types/core.d.ts

declare namespace types {
  interface User {
    name: string;
  }
}

The consuming code is a controller with two methods:

// controller.ts

import { Request, Response, NextFunction } from "express";

const user = { name: "Hiago" };
class UserController {
  getUser(req: Request, res: Response, next: NextFunction) {
    req.user = user;
    return next();
  }

  returnUser(req: Request, res: Response) {
    const { user } = req;

    return res.status(200).json(user);
  }
}

This is working pretty fine. The problem is that since I have namespaces declarations only, I can't import these interfaces in my code. In the future I'd like to auto-generate interfaces like the User shown above, and be able to use them in other parts of my app.

So I've found that declaring a module , like the following, could help me achieve this:

// types/core.d.ts

declare module "core" {
  export namespace types {
    export interface User {
      name: string;
    }
  }
}

Now I'm able to import the User interface using import { types } from "core" wherever I need to have it. But strangely, despite never complaining about anything on the types/express/index.d.ts file, on my controller.ts the compiler gives me a error TS2339: Property 'user' does not exist on type 'Request<ParamsDictionary> .

I've put all the code in this repo , so that anybody willing to help can reproduce this error.

Answer 1

Change your // types/express/index.d.ts to:

import { types } from "core";

declare module 'express' {
  interface Request {
    user: types.User;
  }
}

In your controller.ts you are using the type from module express, not namespace. (in some cases they just reexport it, but it seems express is not the case). With this change it should work.