Express Types in TypeScript

Typed Request and Response

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

interface CreateUserDto {
  name: string;
  email: string;
  password: string;
}

interface UserParams {
  id: string;
}

type CreateUserRequest = Request<{}, {}, CreateUserDto>;
type GetUserRequest = Request<UserParams>;

app.post('/users', (req: CreateUserRequest, res: Response) => {
  const { name, email } = req.body;
  // name and email are typed
});

Augmenting Express Request

import 'express';

declare module 'express' {
  interface Request {
    user?: { id: string; role: string };
    requestId: string;
    startTime: number;
  }
}

// Now Request.user is available everywhere
app.get('/me', (req, res) => {
  console.log(req.user?.id); // typed!
});

Interview Questions

Easy: How do you type Express request parameters?

Medium: How do you augment the Express Request type?

Hard: How would you create a generic request handler type with custom DTO?