Type 'boolean' is not assignable to type 'Observable'

Question

I have that code

method(): Observable<boolean> {
    return this._http.get('sessionId=' + sessionId).map(res=> {
      if (res.status === "success") {
        return true;
      }
      return false;
    });
}

But when sessionId is '' it throws an exception and console logs 401 error

and I add if inside that method:

method(): Observable<boolean> {
    if (sessionId === '')
      return false;
    return this._http.get('sessionId=' + sessionId).map(res=> {
      if (res.status === "success") {
        return true;
      }
      return false;
    });
  }

But now I'm getting an error:

Type 'boolean' is not assignable to type 'Observable'.

How can I solve that?

If I add Observable<boolean> | boolean then I'm getting error that

Property 'map' does not exist on type 'boolean | Observable'.

Possible duplicate of [Type 'Observable<{}>' is not assignable to type 'Observable | boolean '](http://stackoverflow.com/questions/38299484/type-observable-is-not-assignable-to-type-observableboolean-boolean) — Roman C, Feb 11 '17 at 16:44

score 56 · Accepted Answer · edited Apr 06 '21 at 14:29

56

method(): Observable<boolean> {
    if (sessionId === '')
      return false; // <<< obviously not an observable

This should do what you want

import { of, Observable } from 'rxjs';


method(): Observable<boolean> {
    if (sessionId === '')
      return of(false);
    }
    return this._http.get('sessionId=' + sessionId).map(res=> {
      if (res.status === "success") {
        return true;
      }
      return false;
    });
  }

edited Apr 06 '21 at 14:29

Inês Gomes

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answered Feb 11 '17 at 16:39

Günter Zöchbauer

623,577
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19

For Angular 6+ it is now `of()` instead of `Observable.of()` – Sinan Samet Oct 31 '19 at 09:16

score 14 · Answer 2 · answered Jun 11 '18 at 18:03

In addition to accepted answer I would add RxJs v6 case where of does not exist on Observable but could be imported directly from rxjs:

import { Observable, of as observableOf } from 'rxjs'; // since RxJs 6

method(): Observable<boolean> {
  if (sessionId === '')
    return observableOf(false);
  }
  // ...
}

score 1 · Answer 3 · answered Aug 29 '21 at 16:26

For Angular users with STRICT TYPE setting, all other types seem to work OK (not that I tested ALL types... but number, and custom interfaces for example work without the added type declaration)

Using type boolean, this results in error:

_isBoolean$: BehaviorSubject<boolean> = new BehaviorSubject(false);

change to this:

_isBoolean$: BehaviorSubject<boolean> = new BehaviorSubject<boolean>(false);

this works too...

_isBoolean$ = new BehaviorSubject<boolean>(false);
_isBoolean$ = new BehaviorSubject(false);

However, as is quite clear, it removes...the...strict...typing ;)

Type 'boolean' is not assignable to type 'Observable'

3 Answers3

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