Node.js with TypeScript: implementing Type Inference for Express Middleware Function
I'm working with a type inference scenario when trying to define a custom middleware function in my Node.js application using TypeScript and Express (v4.17.1). The middleware is supposed to validate a JWT token and attach the user info to the request object. However, TypeScript is throwing an behavior because it doesn't recognize the extended properties on the `Request` interface. I've tried augmenting the Express `Request` interface but I'm still getting type errors. Here's what my code looks like: ```typescript import express, { Request, Response, NextFunction } from 'express'; import jwt from 'jsonwebtoken'; interface CustomRequest extends Request { user?: { id: string; name: string; }; } const app = express(); const authenticateJWT = (req: CustomRequest, res: Response, next: NextFunction) => { const token = req.header('authorization')?.split(' ')[1]; if (token) { jwt.verify(token, 'your_jwt_secret', (err, user) => { if (err) { return res.sendStatus(403); } req.user = user; next(); }); } else { res.sendStatus(401); } }; app.use(authenticateJWT); app.get('/protected', (req: CustomRequest, res: Response) => { if (req.user) { res.json({ message: 'Protected data', user: req.user }); } else { res.sendStatus(403); } }); app.listen(3000, () => { console.log('Server is running on port 3000'); }); ``` When I run this, I see the following behavior in TypeScript: ``` Property 'user' does not exist on type 'Request'. ``` I've already tried adding a declaration file to augment the Express namespace, but the behavior continues. What am I missing, or how can I properly extend the `Request` type to include my custom properties?