How to return Observable after some Promise get resolved in Ionic 2/Angular 2?

Question

I am trying to return an observable after a successful completion of my Promise, but that function is not returning Observable. To be specific to code, i want to fetch auth

Answer 1

Answer from Sunil worked for my use case, this is my working example. I am using this in my http interceptor to append acces token to the HTTP request

import {from, Observable} from "rxjs";
import {mergeMap} from "rxjs/operators";

 handleTokenExpiration(request: HttpRequest, next: HttpHandler): Observable> {
    if (this.isAccessTokenPresent()) {
      request = request.clone({
        setHeaders: {
          Authorization: `Bearer ${this.getAccessToken()}`
        }
      });
      return next.handle(request);
    } else {
      if (this.isRefreshTokenPresent()) {
        return from(this.refreshToken(this.getRefreshToken())).pipe(mergeMap(res => {
          request = request.clone({
            setHeaders: {
              Authorization: `Bearer ${this.getAccessToken()}`
            }
          });
          return next.handle(request);
        }));
      } else {
        this.logout();
      }
    }
  }