comp-a.ts

function toResponseActions(successSelector, errorSelector){
  return (requests$) => requests$.pipe(
    catchError(err, => errorSelector(err)),
    map(res => successSelector(res))
  )
}

const buttonClicks = fromEvent('button', 'click');

const requests = buttonClicks.pipe(switchMap(() => http.get('foo.json')));

const responses = requests.pipe(
  toResponseActions(
    res => ({type: 'SUCCESS', payload: res.data })),
    err => ({type: 'ERROR', payload: error }))
 )
);