Adding additional properties to session object

Question

I am trying to add additional properties to session object

req.session.confirmationCode = confirmationCode;

but getting an error that confirmationCode property does not exist

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

I have index.d.ts file under types directory where I am adding this prop

declare global {
  namespace session {
    interface SessionData {
      confirmationCode: number;
    }
  }
}

export {};

And this is my tsconfig.json file

{
  "compilerOptions": {
    "target": "es6",
    "module": "commonjs",
    "lib": ["dom", "es6", "es2017", "esnext.asynciterable"],
    "sourceMap": true,
    "outDir": "./dist",
    "moduleResolution": "node",
    "removeComments": true,
    "strict": true,
    "allowSyntheticDefaultImports": true,
    "esModuleInterop": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "resolveJsonModule": true,
    "noImplicitAny": true,
    "noFallthroughCasesInSwitch": true,
    "noImplicitReturns": true,
    "noImplicitThis": true,
    "noUnusedLocals": true,
    "noUnusedParameters": true,
    "noStrictGenericChecks": true
  },
  "exclude": ["node_modules"],
  "include": ["src"]
}

I saw in source code for @types/express-session package that I can extend session object like

declare module "express-session" {
  interface SessionData {
    confirmationCode: number;
  }
}

but when I do this, I get an error that session function is not callable

Type 'typeof import("express-session")' has no call signatures

How can I extend session object properly?

UPD1: And this is how I call session function

app.use(
  session({
    name: "wishlify",
    secret: process.env.SESSION_SECRET,
    resave: false,
    saveUninitialized: false,
    cookie: {
      maxAge: 1000 * 60 * 60 * 24 * 60, // 2 months
      secure: process.env.NODE_ENV === "production",
    },
  })
);

Answer 1

I found an answer in this question.

I added export {}; to index.d.ts file and this is now working as expected.

This line makes file not a script but a module.

The final version of index.d.ts file

declare module "express-session" {
  interface SessionData {
    confirmationCode: number;
  }
}

export {};