Fixing “Property 'user' does not exist on type 'Request'” in Express + TypeScript

If you’ve ever tried adding req.user inside Express middleware while using TypeScript, you’ve probably run into this error:

Property 'user' does not exist on type 'Request'

I hit this while building authentication middleware for my API with JWT and Prisma.

The issue is simple: Express’ default Request type only knows about built-in properties like body, params, and headers. It has no idea about your custom user property.

The Fix

You need to extend Express’ Request interface using declaration merging.

Step 1: Create a type declaration file

src/types/express/index.d.ts

Step 2: Add this definition

import { JwtPayload } from "jsonwebtoken";

declare module 'express-serve-static-core' {
  export interface Request {
    user ?: string | JwtPayload,
  }
}

export {};

NOTES:

• declare module 'express-serve-static-core' is relevant if you're using the newer versions of express in your project. Otherwise, change that line to declare namespace Express.
• The export {} is important — without it, TypeScript may not properly recognize the file.

Step 3: Update tsconfig.json

Make sure TypeScript can see your custom types:

{
  "files": ["./src/types/express/index.d.ts"],
  "compilerOptions": {
    ...
    "typeRoots": [
      "./node_modules/@types",
      "./src/types"
    ],
  },
  ...
}

Step 4: Restart TypeScript + Dev Server

Sometimes VS Code and nodemon cache old types.

• Restart your TS server
  

• Stop and restart your dev server (e.g nodemon)

Result

Now this works cleanly:

req.user = decoded;

No IntelliSense errors. No compiler complaints.

Final Note

This issue looks small, but understanding declaration merging is one of those TypeScript moments that makes backend development much smoother. Anyway, I hope this was helpful. Feel free to leave your thoughts in the comments. Have fun building !!!