example.js

const removeCreativeEpic = (action$) => 
  action$.ofType('REMOVE_CREATIVE')
    .groupBy(action => action.payload.campaignId)
    .mergeMap(
      groupedAction$ => groupedAction$
        .concatMap(action => makeAjax(action)
          .map(response => ({
            type: 'REMOVE_CREATIVE_SUCCESS',
            payload: response,
          })
          .catch(error => ({
            type: 'REMOVE_CREATIVE_ERROR',
            payload: error,
          })
          .takeUntil(
            action$.ofType('REMOVE_CREATIVE_CANCELLED')
              .filter(newAction =>
                newAction.payload.campaignId !== action.payload.campaignId
              )
          )
        )
    )