减少样板代码在redux中关于 reduce重构的应用

原始代码

// 省略了内容
function updateObject(oldObject, newValues) {}
function updateItemInArray(array, itemId, updateItemCallback) {}



function setVisibilityFilter(visibilityState, action) {
    // 从技术上将，我们甚至不关心之前的状态
    return action.filter;
}

function visibilityReducer(visibilityState = 'SHOW_ALL', action) {
    switch(action.type) {
        case 'SET_VISIBILITY_FILTER' : return setVisibilityFilter(visibilityState, action);
        default : return visibilityState;
    }
};


function addTodo(todosState, action) {
    const newTodos = todosState.concat({
        id: action.id,
        text: action.text,
        completed: false
    });

    return newTodos;
}

function toggleTodo(todosState, action) {
    const newTodos = updateItemInArray(todosState, action.id, todo => {
        return updateObject(todo, {completed : !todo.completed});
    });

    return newTodos;
}

function editTodo(todosState, action) {
    const newTodos = updateItemInArray(todosState, action.id, todo => {
        return updateObject(todo, {text : action.text});
    });

    return newTodos;
}

function todosReducer(todosState = [], action) {
    switch(action.type) {
        case 'ADD_TODO' : return addTodo(todosState, action);
        case 'TOGGLE_TODO' : return toggleTodo(todosState, action);
        case 'EDIT_TODO' : return editTodo(todosState, action);
        default : return todosState;
    }
}

function appReducer(state = initialState, action) {
    return {
        todos : todosReducer(state.todos, action),
        visibilityFilter : visibilityReducer(state.visibilityFilter, action)
    };
}

使用样板代码后不在需要switch语句，有些代码洁癖很讨厌使用if和switch的条件判断，使用样板代码后可以使得代码可以配置

// 省略了内容
function updateObject(oldObject, newValues) {}
function updateItemInArray(array, itemId, updateItemCallback) {}

function createReducer(initialState, handlers) {
  return function reducer(state = initialState, action) {
    if (handlers.hasOwnProperty(action.type)) {
      return handlers[action.type](state, action)
    } else {
      return state
    }
  }
}


// 省略了内容
function setVisibilityFilter(visibilityState, action) {}

const visibilityReducer = createReducer('SHOW_ALL', {
    'SET_VISIBILITY_FILTER' : setVisibilityFilter
});

// 省略了内容
function addTodo(todosState, action) {}
function toggleTodo(todosState, action) {}
function editTodo(todosState, action) {}

const todosReducer = createReducer([], {
    'ADD_TODO' : addTodo,
    'TOGGLE_TODO' : toggleTodo,
    'EDIT_TODO' : editTodo
});

function appReducer(state = initialState, action) {
    return {
        todos : todosReducer(state.todos, action),
        visibilityFilter : visibilityReducer(state.visibilityFilter, action)
    };
}