text: //Atate arg is not application state,
  //only the state this reducer is responsible for
  export default function ActiveBook (state = null, action) { //if the arg is undefined, set it null
    switch (action.type) {
      case 'BOOK_SELECTED':
        return action.payload;
  
        break;
      default:
  
    }
    //base case
    return state
  }
  