CODEWITHSUNDEEP
angularrxjs
Basil Bear
Basil Bear

Reputation: 463

RXJS - Error handling in chain of observables

I have just learned not to nest subscribes, so instead I am using switchMapTo as a means of starting each successive step on the completion of the previous step:

e.g.

    const s1$ = this.retrieveAnnualLeaveVariables();       
    const s2$ = s1$.switchMapTo(this.initialise());      
    const s3$ = s2$.switchMapTo(this.retrieveData());
    const s4$ = s3$.switchMapTo(this.accumulateAnnualLeaveRecords());
    s4$.subscribe(() => outerStream.next(someResults) ) // pass the results to the outerStream

What I am unclear about now, is how to integrate error handling in a concise manner, so that I can send an error signal to outerStream in the event of a problem, encountered anywhere within the chain.

I have tried attaching the following to the first 

    .catch(e => {
        return Observable.of<any>([]);
    });

However:

Thanks for any assistance!

Upvotes: 3

Views: 3309

Answers (1)

M4R1KU
M4R1KU

Reputation: 718

First you should chain the operators on your observable instead of creating a new constant each time you call switchMapTo. Then you get this.

this.retrieveAnnualLeaveVariables()
    .switchMapTo(this.initialise())
    .switchMapTo(this.retrieveData())
    .switchMapTo(this.accumulateAnnualLeaveRecords())
    .subscribe(() => outerStream.next(someResults))

Then if you have this you can add the catch before the subscribe. In the catch you can either return a new "fallback" value as observable, an empty observable or throw another error.

If you want to stop the chain then you should return an empty Observable via Observable.empty(). If you return this the Observable will complete without calling the given subscribe function.

Result:

this.retrieveAnnualLeaveVariables()
    .switchMapTo(this.initialise())
    .switchMapTo(this.retrieveData())
    .switchMapTo(this.accumulateAnnualLeaveRecords())
    .catch(() => Observable.empty())
    .subscribe(() => outerStream.next(someResults))

Upvotes: 1

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