javascript - rxjs: returning value with pipe(map) - Stack Overflow

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How to return value when using pipe and map, like in this scenario:

return this.service.someEvent().pipe(
  map(x => {
    return this.service.someValue;
  })
)

but the value is never returned since never subscrubed to the event, if i use it like this:

const a = this.service.someEvent().pipe(
  map(x => {
    return this.service.someValue;
  })
)

return a.subscribe();

i get an error (i know this is wrong).

TS2322: Type 'Subscription' is not assignable to type 'boolean | Observable<boolean> | Promise<boolean>'.   Type 'Subscription' is not assignable to type 'Promise<boolean>'.     Property 'then' is missing in type 'Subscription'.

So i need i way to return the value.

UPDATE: the better description (i need to duplicate this code with the latest version of rxjs):

canActivate(next: ActivatedRouteSnapshot,
               state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
  return this.service.something().map(x => {
    if (x) {
      return true;
    } else {
      return false;
    }
  })

}

need to do it with map inside pipe (as i understood).

How to return value when using pipe and map, like in this scenario:

return this.service.someEvent().pipe(
  map(x => {
    return this.service.someValue;
  })
)

but the value is never returned since never subscrubed to the event, if i use it like this:

const a = this.service.someEvent().pipe(
  map(x => {
    return this.service.someValue;
  })
)

return a.subscribe();

i get an error (i know this is wrong).

TS2322: Type 'Subscription' is not assignable to type 'boolean | Observable<boolean> | Promise<boolean>'.   Type 'Subscription' is not assignable to type 'Promise<boolean>'.     Property 'then' is missing in type 'Subscription'.

So i need i way to return the value.

UPDATE: the better description (i need to duplicate this code with the latest version of rxjs):

canActivate(next: ActivatedRouteSnapshot,
               state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
  return this.service.something().map(x => {
    if (x) {
      return true;
    } else {
      return false;
    }
  })

}

need to do it with map inside pipe (as i understood).

• javascript
• angular
• rxjs
• reactivex

Share Improve this question Follow edited May 16, 2018 at 17:02 Igor asked May 16, 2018 at 15:34 IgorIgor 27722 gold badges77 silver badges1616 bronze badges 1

• 1 This looks like you're trying to call return a.subscribe(); in a method whose typings say it should return Observable. Function subscribe() returns Subscription instance – martin Commented May 16, 2018 at 15:38

Add a ment  | 

1 Answer 1

Sorted by: Reset to default 3

You can simply return the observable itself from the "canActivate" guard :-

canActivate(next: ActivatedRouteSnapshot, state: RouterStateSnapshot): Observable<boolean> | Promise<boolean> | boolean {
  return this.service.something().pipe(map(x => {
    if (x) {
      return true;
    } else {
      return false;
    }
  }));
}

Routing will proceed only after the returned observable is plete and its emitted value is true. So you don't actually have to worry about subscribing to that observable angular router will handle it of its own.

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