Rxjs make sequential calls using concatMap

Question

I would like to make two sequentially calls (if the first one is completed, call the second one):

My Code is like:

        myApiClient
        .firstApiCall()
        .pipe(take(1),
            concatMap (firstResult => {
            doSomethingWithResponse(firstResult);
            return myApiClient.secondApiCall();
        }), take(1))
        .subscribe(secondResult => {
            doSomethingWithResponse(firstResult);
        }, error => {
            catchSecondApiCallError(error);
        });

First question: is that the right way to make sequential calls? Second question: How could I catch the error for the first Call?

Answer 1

Yes, that is the right way to chain sequential api calls using rxjs. For the second question you may make use of the catchError operator.

    myApiClient
    .firstApiCall()
    .pipe(
        take(1),
        catchError(e => {
          console.log('Error caught from first api ', e);
          return EMPTY;
        }),
        concatMap (firstResult => {
          doSomethingWithResponse(firstResult);
          return myApiClient.secondApiCall();
    }), take(1))
    .subscribe(secondResult => {
        doSomethingWithResponse(secondResult);
    }, error => {
        catchSecondApiCallError(error);
    });

EMPTY is imported from:

import { EMPTY } from 'rxjs';