distinctUntillChanges delay notification for same user but not for others

delay notif.js

    let usersToDelay = {}

    action$
        .ofType(OPEN_NOTIFICATION)
        .distinctUntilChanged( (prev, next) => {
            let userName = next.userName;
            if (usersToDelay[userName]) {
              return true; // do not emit notification
            }
            setTimeout(() => {delete usersToDelay[userName];}, 3000);
            return false; //emit if another use;
         }
        )