animal-immer.state.ts

@State<AnimalsStateModel>({
  name: 'animals',
  defaults: {
    zebra: {
      food: [],
      name: 'zebra'
    },
    panda: {
      food: [],
      name: 'panda'
    }
  }
})
export class AnimalState {
  @Selector()
  @ImmutableSelector()
  public static zebraFood(state: AnimalsStateModel): string[] {
    return state.zebra.food.reverse();
  }

  @Action(Add)
  @ImmutableContext()
  public Add({ setState }: StateContext<AnimalsStateModel>, { payload }: Add): void {
    setState((state: AnimalsStateModel) => ({
      state.zebra.food.push(payload);
      return state;
    }));
  }
}