const counter = createReducer<CounterState, CounterAction>(initialState, {
  [INCREASE]: (state) => ({ count: state.count + 1 }),
  [DECREASE]: (state) => ({ count: state.count - 1 }),
  [INCREASE_BY]: (state, action) => ({ count: state.count + action.payload }),
  });

const counter = createReducer<CounterState, CounterAction>(initialState)
  .handleAction(INCREASE, (state) => ({ count: state.count + 1 }))
  .handleAction(DECREASE, (state) => ({ count: state.count - 1 }))
  .handleAction(INCREASE_BY, (state, action) => ({
    count: state.count + action.payload,
  }));