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))

```