83 lines
4.0 KiB
Markdown
83 lines
4.0 KiB
Markdown
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---
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id: 5a24c314108439a4d4036158
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title: Never Mutate State
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 从不改变国家
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---
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## Description
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<section id="description">这些最后的挑战描述了在Redux中实施状态不变性关键原则的几种方法。不可变状态意味着您永远不会直接修改状态，而是返回状态的新副本。如果你随着时间的推移拍摄了一个Redux应用程序状态的快照，你会看到<code>state 1</code> ， <code>state 2</code> ， <code>state 3</code> ， <code>state 4</code> ， <code>...</code>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<code>string</code> ， <code>number</code> ， <code>array</code>还是<code>object</code> 。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， <code>array</code>或<code>object</code>是可变的。实际上，您的状态可能包含<code>array</code>或<code>object</code> ，因为它们是用于表示许多类型信息的有用数据结构。 </section>
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## Instructions
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<section id="instructions">代码编辑器中有一个<code>store</code>和<code>reducer</code>器，用于管理待办事项。完成在<code>ADD_TO_DO</code>中写入<code>ADD_TO_DO</code>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<code>action.todo</code>的项目附加到结尾。 </section>
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## Tests
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<section id='tests'>
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```yml
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tests:
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- 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。
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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.");'
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- text: <code>addToDo</code>和<code>immutableReducer</code>都应该是函数。
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testString: 'assert(typeof addToDo === "function" && typeof immutableReducer === "function", "<code>addToDo</code> and <code>immutableReducer</code> both should be functions.");'
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- 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。
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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.");'
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```
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</section>
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## Challenge Seed
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<section id='challengeSeed'>
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<div id='jsx-seed'>
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```jsx
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const ADD_TO_DO = 'ADD_TO_DO';
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// A list of strings representing tasks to do:
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const todos = [
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'Go to the store',
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'Clean the house',
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'Cook dinner',
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'Learn to code',
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];
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const immutableReducer = (state = todos, action) => {
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switch(action.type) {
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case ADD_TO_DO:
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// don't mutate state here or the tests will fail
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return
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default:
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return state;
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}
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};
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// an example todo argument would be 'Learn React',
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const addToDo = (todo) => {
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return {
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type: ADD_TO_DO,
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todo
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}
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}
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const store = Redux.createStore(immutableReducer);
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```
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</div>
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</section>
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## Solution
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<section id='solution'>
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```js
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// solution required
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```
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</section>
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