4.0 KiB
4.0 KiB
id | title | challengeType | isRequired | videoUrl | localeTitle |
---|---|---|---|---|---|
5a24c314108439a4d4036158 | Never Mutate State | 6 | false | 从不改变国家 |
Description
state 1
, state 2
, state 3
, state 4
, ...
等等,其中每个状态可能与最后一个状态相似,但每个状态是一个独特的数据。事实上,这种不变性提供了您可能听说过的时间旅行调试等功能。 Redux不会在其商店或减少者中主动强制执行状态不变性,而责任落在程序员身上。幸运的是,JavaScript(尤其是ES6)提供了一些有用的工具,可用于强制执行状态的不变性,无论是string
, number
, array
还是object
。请注意,字符串和数字是原始值,并且本质上是不可变的。换句话说,3总是3.您不能更改数字3的值。但是, array
或object
是可变的。实际上,您的状态可能包含array
或object
,因为它们是用于表示许多类型信息的有用数据结构。 Instructions
store
和reducer
器,用于管理待办事项。完成在ADD_TO_DO
中写入ADD_TO_DO
情况,以向状态附加新的待办事项。使用标准JavaScript或ES6可以通过几种方法实现此目的。看看是否可以找到一种方法来返回一个新数组,其中action.todo
的项目附加到结尾。 Tests
tests:
- text: Redux存储应该存在并使用等于代码编辑器中的<code>todos</code>数组的状态进行初始化。
testString: 'assert((function() { const todos = [ "Go to the store", "Clean the house", "Cook dinner", "Learn to code" ]; const initialState = store.getState(); return Array.isArray(initialState) && initialState.join(",") === todos.join(","); })(), "The Redux store should exist and initialize with a state equal to the <code>todos</code> array in the code editor.");'
- text: <code>addToDo</code>和<code>immutableReducer</code>都应该是函数。
testString: 'assert(typeof addToDo === "function" && typeof immutableReducer === "function", "<code>addToDo</code> and <code>immutableReducer</code> both should be functions.");'
- text: 在Redux存储上调度<code>ADD_TO_DO</code>类型的操作应该添加<code>todo</code> ,不应该改变状态。
testString: 'assert((function() { const initialState = store.getState(); const isFrozen = DeepFreeze(initialState); store.dispatch(addToDo("__TEST__TO__DO__")); const finalState = store.getState(); const expectedState = [ "Go to the store", "Clean the house", "Cook dinner", "Learn to code", "__TEST__TO__DO__" ]; return( isFrozen && DeepEqual(finalState, expectedState)); })(), "Dispatching an action of type <code>ADD_TO_DO</code> on the Redux store should add a <code>todo</code> item and should NOT mutate state.");'
Challenge Seed
const ADD_TO_DO = 'ADD_TO_DO';
// A list of strings representing tasks to do:
const todos = [
'Go to the store',
'Clean the house',
'Cook dinner',
'Learn to code',
];
const immutableReducer = (state = todos, action) => {
switch(action.type) {
case ADD_TO_DO:
// don't mutate state here or the tests will fail
return
default:
return state;
}
};
// an example todo argument would be 'Learn React',
const addToDo = (todo) => {
return {
type: ADD_TO_DO,
todo
}
}
const store = Redux.createStore(immutableReducer);
Solution
// solution required