Session object not modifiable in typescript (while using @types/express-session)

I’ve been using express-session in various express applications, but never with typescript. Disclaimer: This might be a bug with @types/express-session, but I figure this is the right community to ask either way, so here’s what’s happening.

The session object is essentially just not modifiable, ie I can’t seem to add properties to it, and, perhaps because of a recent update, all methods of fixing this I’ve found either don’t work or just break the whole thing.

In this example use case:

router.get("/example", (req, res) => {
	console.log(req.session); // Works
	req.session.username = "mine" // Fails
	req.session.destroy(data => console.log(data)); // Works
	res.send('something')
});

I get the following error:

Property 'username' does not exist on type 'Session & Partial<SessionData>'

Not sure if this is in any way useful, but these are my session options

const sessionConfig: session.SessionOptions = {
	name: "uid",
	secret,
	store: new RedisStore({
		client: redisClient,
		disableTTL: true,
		disableTouch: true,
	}),
	cookie: {
		maxAge: 1000000000000999,
		httpOnly: true,
		sameSite: "lax",
		secure: __prod__,
	},
	saveUninitialized: false,
	resave: false,
};

I have attempted to create a separate type combining express.Request and the session options, but I can’t really get that to work either, and I’m assuming there’s a bit more elegant way of dealing with this.

Thank your for your time.

[jasonlimantoro]

1. Make sure your tsconfig.json’s typeroots declares custom types first, before the node_modules’s.

"typeRoots": ["./src/typings", "./node_modules/@types"]

1. Declare definition file

// ./src/typings/express-session/index.d.ts
import "express-session"; // don't forget to import the original module

declare module "express-session" {
    interface SessionData {
        username: string // whatever property you like
    }
}

That should be enough, hope this helps everyone who is stuck on Typescript hole 😄

[randomicons]

Add this to a file in your project ( ie types.ts etc.)

declare module "express-session" {
  interface SessionData {
    username: string
  }
}

You can add all of your custom fields in session inside of the SessionData interface.