CODEWITHSUNDEEP
javascriptrxjsobservable
Guerric P
Guerric P

Reputation: 31805

How to bring errors back into the normal events flow?

In this example, the source Observable generates numbers between 0 and 6, and considers 6 as an error. How can I create a target Observable that brings the errors back to the normal events flow.

I tried this but it stops working when an error occurs.

const { of, interval, throwError } = rxjs;
const { switchMap, map, catchError } = rxjs.operators;

const source = interval(1000).pipe(
    map(() => Math.floor(Math.random() * 7)),
    switchMap(result => result < 6 ? of(result) : throwError(result)));
    
const target = source.pipe(catchError(err => of(err)));

target.subscribe(console.log);
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.5/rxjs.umd.min.js"></script>

Upvotes: 0

Views: 56

Answers (2)

Andrei Gătej
Andrei Gătej

Reputation: 11924

Just wanted to add that catchError is given a second argument which represents the caught observable. Basically, if you want to re-subscribe to the source when an error occurs, you can also do this:

src$.pipe(
  catchError((err, caught$) => caught$)
).subscribe(/* ... */)

Upvotes: 1

Guerric P
Guerric P

Reputation: 31805

As the contract says here: http://reactivex.io/documentation/contract.html

When an Observable does issue an OnCompleted or OnError notification, the Observable may release its resources and terminate, and its observers should not attempt to communicate with it any further.

That means we have to return the source Observable again after an error occurs, like this:

const { of, interval, concat, throwError } = rxjs;
const { switchMap, map, catchError } = rxjs.operators;

const source = interval(1000).pipe(
        map(() => Math.floor(Math.random() * 7)),
        switchMap(result => result < 6 ? of(result) : throwError(result)));

const target = source => source.pipe(catchError(err => concat(of('Error: ' + err), target(source))));

target(source).subscribe(console.log);
<script src="https://cdnjs.cloudflare.com/ajax/libs/rxjs/6.5.5/rxjs.umd.min.js"></script>

Upvotes: 1

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