2018-10-10 22:03:03 +00:00
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---
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id: 5a24c314108439a4d4036159
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challengeType: 6
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2020-09-07 08:16:17 +00:00
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forumTopicId: 301452
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2020-10-01 15:54:21 +00:00
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title: 在数组中使用扩展运算符
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2018-10-10 22:03:03 +00:00
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---
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## Description
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2020-09-07 08:16:17 +00:00
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<section id='description'>
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ES6 中有助于在 Redux 中强制执行状态不变性的一个解决方案是扩展运算符:<code>...</code>。扩展运算符具有很多的应用,其中一种非常适合通过一个已有的数组生成一个新数组。这是相对较新的,但常用的语法。例如,如果你有一个数组<code>myArray</code>并写:
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<code>let newArray = [...myArray];</code>
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<code>newArray</code>现在是<code>myArray</code>的克隆。两个数组仍然在内存中单独存在。如果你执行像<code>newArray.push(5)</code>这样的突变,<code>myArray</code>不会改变。<code>...</code>有效<i>将<code>myArray</code>中的值</i>传播到新数组中。要克隆数组但在新数组中添加其他值,可以编写<code>[... myArray,'new value']</code>。这将返回一个由<code>中的值组成的新数组。</code>myArray</code>和字符串<code>'new value'</code>作为最后一个值。扩展语法可以像这样在数组组合中多次使用,但重要的是要注意它只做一个浅拷贝这就是说,它只为一维数组提供了不可变的数组操作。
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</section>
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2018-10-10 22:03:03 +00:00
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## Instructions
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2020-09-07 08:16:17 +00:00
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<section id='instructions'>
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添加待办事项时,使用 spread 运算符返回新的状态副本。
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</section>
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2018-10-10 22:03:03 +00:00
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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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2020-09-07 08:16:17 +00:00
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- text: Redux store 应该存在并初始化一个<code>[Do not mutate state!]</code>的状态。
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2020-02-17 16:40:55 +00:00
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testString: assert((function() { const initialState = store.getState(); return ( Array.isArray(initialState) === true && initialState[0] === 'Do not mutate state!'); })());
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2020-09-07 08:16:17 +00:00
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- text: <code>addToDo</code>和<code>immutableReducer</code>都应该是一个函数。
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2020-02-17 16:40:55 +00:00
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testString: assert(typeof addToDo === 'function' && typeof immutableReducer === 'function');
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2020-09-07 08:16:17 +00:00
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- text: 在 Redux store 上 dispatch 一个类型为<code>ADD_TO_DO</code> aciton 应该添加一个<code>todo</code>项,并且不应该改变 state。
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2020-02-17 16:40:55 +00:00
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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 = [ 'Do not mutate state!', '__TEST__TO__DO__' ]; return( isFrozen && DeepEqual(finalState, expectedState)); })());
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2020-09-07 08:16:17 +00:00
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- text: 应使用扩展运算符返回新的 state。
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2020-02-17 16:40:55 +00:00
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testString: getUserInput => assert(getUserInput('index').includes('...state'));
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2018-10-10 22:03:03 +00:00
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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 immutableReducer = (state = ['Do not mutate state!'], action) => {
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switch(action.type) {
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case 'ADD_TO_DO':
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2020-09-07 08:16:17 +00:00
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// 不要在这里改变 state 否则测试会失败。
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2018-10-10 22:03:03 +00:00
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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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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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2020-09-07 08:16:17 +00:00
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2018-10-10 22:03:03 +00:00
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```js
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2020-09-07 08:16:17 +00:00
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const immutableReducer = (state = ['Do not mutate state!'], action) => {
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switch(action.type) {
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case 'ADD_TO_DO':
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return [
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...state,
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action.todo
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];
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default:
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return state;
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}
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};
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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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2018-10-10 22:03:03 +00:00
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```
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2020-08-13 15:24:35 +00:00
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2020-09-07 08:16:17 +00:00
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</section>
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