Angular 6 / NGRX Combine Reducers

import { ActionReducerMap } from '@ngrx/store';
import { reducer as counterReducer, key as counterKey } from './counter';
import { reducer as profileReducer, key as profileKey } from './profile';

export interface IAppState {
  [counterKey]: any;
  [profileKey]: any;
}

export const reducers: ActionReducerMap<IAppState> = {
  [counterKey]: counterReducer,
  [profileKey]: profileReducer,
};