text: const initialState = {
      age:20
  };
  
  const reducer = (state=initialState, action) => {
      const newState = {...state};
  
      switch(action.type){
          case 'AGE_UP_ASYNC':
              newState.age += action.value;
              break;
          
          case 'AGE_DOWN': 
              newState.age -= action.value;
              break;
      }
      return newState;
  };
  
  export default reducer;