RxJS add catch() to an Observable that's been shared

I have the following code I'm using in my Angular (4.0) application during $http calls.

return this.httpComponent.post(serviceUrl, request, args)
            .map((res: any) => res.json() as R)
            .catch((error: any) => Observable.throw(error.json().error || error.json().errorMessage || 'Server error'));

After testing this I realized multiple subscriptions were triggering the request multiple times. Thanks to this post: Angular2 http.post gets executed twice I found out I needed to share() the result.

This works to get rid of the multiple calls but now it seems my catch() method isn't being hit. I want my catch() to throw the error.

I tried the two options below but they did not work:

return this.httpComponent.post(serviceUrl, request, args)
    .map((res: any) => res.json() as R)
    .share()
    .catch((error: any) => Observable.throw(error.json().error || error.json().errorMessage || 'Server error'));

return this.httpComponent.post(serviceUrl, request, args)
    .map((res: any) => res.json() as R)
    .catch((error: any) => Observable.throw(error.json().error || error.json().errorMessage || 'Server error') 
    .share()); //This doesn't make sense since my catch() isn't returning an Observable

Anyone know how I can share() and catch(throw...) at the same time?

Solution

The second option you've included in your question attaches the catch to the Observable.throw. If that is corrected, you should see the behaviour you are expecting:

const source = Rx.Observable
  .interval(500)
  .map((value) => {
    if (value === 2) {
      throw new Error("Boom!");
    }
    console.log(`value: ${value}`)
    return value;
  })
  .catch((error) => Rx.Observable.throw(new Error(`Re-thrown ${error.message}`)))
  .share();

source.subscribe(
  (value) => console.log(`subscription 1: ${value}`),
  (error) => console.log(`subscription 1: ${error}`)
);
source.subscribe(
  (value) => console.log(`subscription 2: ${value}`),
  (error) => console.log(`subscription 2: ${error}`)
);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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