我想知道在reducer中而不是例如使用switch case语法有什么好处对象映射语法？
除了切换用例,我还没有遇到任何使用其他语句的示例,我想知道为什么没有其他选择.
请描述您对两种方式的优缺点的想法(仅在有正当理由的情况下).

const initialState = {
  visibilityFilter: 'SHOW_ALL',todos: []
};

// object mapping Syntax
function reducer(state = initialState,action){
  const mapping = {
    SET_VISIBILITY_FILTER: (state,action) => Object.assign({},state,{
      visibilityFilter: action.filter
    }),ADD_TODO: (state,{
      todos: state.todos.concat({
        id: action.id,text: action.text,completed: false
      })
    }),TOGGLE_TODO: (state,{
      todos: state.todos.map(todo => {
        if (todo.id !== action.id) {
          return todo
        }

        return Object.assign({},todo,{
          completed: !todo.completed
        })
      })
    }),EDIT_TODO: (state,{
          text: action.text
        })
      })
    })
  };
  return mapping[action.type] ? mapping[action.type](state,action) : state
}

// switch case Syntax
function appReducer(state = initialState,action) {
  switch (action.type) {
    case 'SET_VISIBILITY_FILTER': {
      return Object.assign({},{
        visibilityFilter: action.filter
      })
    }
    case 'ADD_TODO': {
      return Object.assign({},{
        todos: state.todos.concat({
          id: action.id,completed: false
        })
      })
    }
    case 'TOGGLE_TODO': {
      return Object.assign({},{
        todos: state.todos.map(todo => {
          if (todo.id !== action.id) {
            return todo
          }

          return Object.assign({},{
            completed: !todo.completed
          })
        })
      })
    }
    case 'EDIT_TODO': {
      return Object.assign({},{
            text: action.text
          })
        })
      })
    }
    default:
      return state
  }
}