javascript - How to handle error and return observable while subscribe inside an observable function in Rxjs Angular - Stack Ove

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I want to check one api call inside an observable which I will subscribe in a ponent. As written below, I want to run my observable in this manner but it is not working. What changes shall I do to this code to make it work. Whenever I try to subscribe through it especially through the scenario when someObservableWrittenInTheSameService returns with an error 404, I want to return url2.

getfunction(submissionId: string ){

if (some condition) {
   this.someObservableWrittenInTheSameService(parameter).subscribe(
    (httpValue: any) => {
      let url = '';
      if (httpValue.code === 200) {
         return this.http.get(url1); 
      }
    }, err => {
      if (err.code === 404) {
        return this.http.get(url2);
      }
      
    }
  )
}

  let url3
  return this.http.get(url3);
}

This function is then is called in a ponent where it is subscribed. But whenever someObservableWrittenInTheSameService return 404, the subscription always fails and go to error block in the ponent.

I want to check one api call inside an observable which I will subscribe in a ponent. As written below, I want to run my observable in this manner but it is not working. What changes shall I do to this code to make it work. Whenever I try to subscribe through it especially through the scenario when someObservableWrittenInTheSameService returns with an error 404, I want to return url2.

getfunction(submissionId: string ){

if (some condition) {
   this.someObservableWrittenInTheSameService(parameter).subscribe(
    (httpValue: any) => {
      let url = '';
      if (httpValue.code === 200) {
         return this.http.get(url1); 
      }
    }, err => {
      if (err.code === 404) {
        return this.http.get(url2);
      }
      
    }
  )
}

  let url3
  return this.http.get(url3);
}

This function is then is called in a ponent where it is subscribed. But whenever someObservableWrittenInTheSameService return 404, the subscription always fails and go to error block in the ponent.

• javascript
• angular
• rxjs

Share Improve this question Follow asked Mar 7, 2022 at 15:52 Aman AhmadAman Ahmad 1311 gold badge11 silver badge44 bronze badges 4

• You should watch catchError operator to check if it match your expectations rxjs.dev/api/operators/catchError – Maxime Chevallier Commented Mar 7, 2022 at 15:55
• Your question is not clear This function is then is called in a ponent where it is subscribed. But whenever someObservableWrittenInTheSameService return 404, the subscription always fails and go to error block in the ponent. . This is working as expected – brk Commented Mar 7, 2022 at 16:01
• @MaximeChevallier Yeah solution would involve this. – Aman Ahmad Commented Mar 8, 2022 at 17:20
• @brk It is not working as intended. I followed the approach given by ruth to make it work. – Aman Ahmad Commented Mar 8, 2022 at 17:22

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1 Answer 1

Sorted by: Reset to default 4

1. You could use RxJS iif function to return an observable conditionally.
2. Use RxJS higher order mappping operator switchMap to map from one observable to another. More info here.
3. Use catchError operator to perform error handling. From it's body you could either return the HTTP request or forward the error (using throwError) or even plete the observable (using EMPTY constant) based on your requirement.

Try the following

import { Observable, EMPTY, iif, throwError } from 'rxjs';
import { switchMap, catchError } from 'rxjs/operators';

getfunction(submissionId: string): Observable<any> {      // <-- observable must be returned here
  const obs1$ = this.someObservableWrittenInTheSameService(parameter).pipe(
    switchMap((httpValue: any) => 
      iif(
        () => httpValue.code === 200,
        this.http.get(url1),
        EMPTY                                             // <-- plete the observable if code is other than 200
      )
    ),
    catchError((error: any) =>                            // <-- `catchError` operator *must* return an observable
      iif(
        () => error.code === 404,
        this.http.get(url2),
        throwError(error)                                 // <-- you could also return `EMPTY` to plete the observable
      )
  )

  const obs2$ = this.http.get(url3);

  return iif(
    () => someCondition,
    obs1$,
    obs2$
  );
}

In this case you'd subscribe to the getFunction() function where it's used.

For eg.

this.getFunction('some value').subscribe({
  next: (value: any) => { },
  error: (error: any) => { },
  plete: () => { }
});

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