How to return observable from subscribe

You can't return an observable from subscribe but if you use map instead of subscribe then an Observable is returned.

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {    // get route to be activated    this.routeToActivate = route.routeConfig.path;    // get user access levels            return this._firebase.isUserAdminObservable        .map(user => {           // do something here           // user.access_level;           return true;         })        .first(); // for the observable to complete on the first event (usually required for `canActivate`)        // first needs to be imported like `map`, ...}canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Observable<boolean> {    // get route to be activated    this.routeToActivate = route.routeConfig.path;    let subject = new Subject();    // get user access levels            this._firebase.isUserAdminObservable        .map(user => {          let accessLevel = user.access_level;           if (accessLevel === 'admin' ) {             subject.emit(true);             subject.complete();          }           return user;        });     return subject;}

Couldn't we just use pipe with map from import { map } from 'rxjs/operators';?

import { map } from 'rxjs/operators';@Injectable({  providedIn: 'root'})export class SearchHostService {  constructor(private readonly http: HttpClient) {}  searchForHosts(searchString: string): Observable<Employee[]> {    return this.http      .get<Employee[]>('./assets/host-users.json')      .pipe(        map(employees =>          employees.filter(({ displayName }) =>            displayName.toLowerCase().startsWith(searchString),          ),        ),      );  }}

We can convert the Observable object to promise using toPromise method.so the code can be implemented as followed:

canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot):Promise<boolean> {        // get route to be activated        this.routeToActivate = route.routeConfig.path;        // get user access levels                return this._firebase.isUserAdmin            .map(user => {                return (user.access_level === 'admin');            }).toPromise();    }