How to catch error in Observable.forkJoin(...)?

Question

I use Observable.forkJoin() to handle the response after both HTTP calls finishes, but if either one of them returns an error, how can I catch that error?

Observable.forkJoin(
  this.http.post<any[]>(URL, jsonBody1, postJson) .map((res) => res),
  this.http.post<any[]>(URL, jsonBody2, postJson) .map((res) => res)
)
.subscribe(res => this.handleResponse(res))

Answer 1

You may catch the error in each of your observables that are being passed to forkJoin:

// Imports that support chaining of operators in older versions of RxJS
import {Observable} from 'rxjs/Observable';
import {forkJoin} from 'rxjs/add/observable/forkJoin';
import {of} from 'rxjs/add/observable/of';
import {map} from 'rxjs/add/operator/map';
import {catch} from 'rxjs/add/operator/catch';

// Code with chaining operators in older versions of RxJS
Observable.forkJoin(
  this.http.post<any[]>(URL, jsonBody1, postJson) .map((res) => res)).catch(e => Observable.of('Oops!')),
  this.http.post<any[]>(URL, jsonBody2, postJson) .map((res) => res)).catch(e => Observable.of('Oops!'))
)
.subscribe(res => this.handleResponse(res))

Also note that if you use RxJS6, you need to use catchError instead of catch, and pipe operators instead of chaining.

// Imports in RxJS6
import {forkJoin, of} from 'rxjs';
import {map, catchError} from 'rxjs/operators';

// Code with pipeable operators in RxJS6
forkJoin(
  this.http.post<any[]>(URL, jsonBody1, postJson) .pipe(map((res) => res), catchError(e => of('Oops!'))),
  this.http.post<any[]>(URL, jsonBody2, postJson) .pipe(map((res) => res), catchError(e => of('Oops!')))
)
  .subscribe(res => this.handleResponse(res))