error TS2339: Property 'user' does not exist on type 'Session & Partial<SessionData>' code example
Example: Property 'userId' does not exist on type 'Session & Partial'.ts(2339)
//After updating express-session, it changes from sessionData to session.
//so you'll have to merge declarations
declare module "express-session" {
interface Session {
user: string;
}
}