RxJS how to return Observable with default error handling function

Question

In my application I have some methods returning an Observable:

public myMethodReturningObs(...): Observable {
  return this.http.get(...); // this will return an Observable
}

then I call this method in several places around my application:

this.service.myMethodReturningObs().subscribe(
 (data) => { /* do something with data */ },
 (error) => { console.log('Error!'); }
);

// ...

this.service.myMethodReturningObs().subscribe(
 (data) => { /* do something else with data */ },
 (error) => { console.log('Error!'); }
);

I was wondering if there is a way inside myMethodReturningObs(...) to attach the a default error handling function, which in my example would be console.log('Error!');, so I don't have to repeat it every time I subscribe to the Observable returned by myMethodReturningObs(...).

Ideally I need something like:

public myMethodReturningObs(...): Observable {
  return this.http.get(...)
   .onError({ console.log('Error!'); }); // this will return an Observable
}

so then I can just do:

this.service.myMethodReturningObs().subscribe(
 (data) => { /* do something with data */ }
);

// ...

this.service.myMethodReturningObs().subscribe(
 (data) => { /* do something else with data */ }
);

udalmik · Accepted Answer · 2017-11-23 11:40:51Z

2

You can catch error in base observable, log it and propogate further

public myMethodReturningObs(...): Observable {
  return this.http.get(...)
        .catch(e => {
          // log error
          console.error('Failed', e);
          // return same error, so subscriptions also fail
          return Rx.Observable.throw(e)
        });
}

edited Nov 23, 2017 at 11:40

answered Nov 23, 2017 at 10:49

udalmik

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3 Comments

Francesco Borzi Over a year ago

it works, but now my unit test are broken: TypeError: Cannot read property 'catch' of undefined

udalmik Over a year ago

Seems you mocked http service and it return undefined. You can adjust it to return empty Observable.

Francesco Borzi Over a year ago

done it, but now I'm getting another error:

Expected $[0] to be a kind of ScalarObservable, but was Observable({ _isScalar: false, source: ScalarObservable({ _isScalar: true, value: 'mock', scheduler: null }), operator: CatchOperator({ selector: Function, caught: <circular reference: Object> }) }).

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