74 lines
3.5 KiB
Markdown
74 lines
3.5 KiB
Markdown
---
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id: 5a24c314108439a4d4036159
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title: Use the Spread Operator on Arrays
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 在阵列上使用Spread Operator
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---
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## Description
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<section id="description"> ES6的一个解决方案是帮助在Redux中强制执行状态不变性，它是扩展运算符： <code>...</code>扩展运算符具有各种应用程序，其中一个非常适合于从现有阵列生成新阵列的先前挑战。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>并且写： <code>let newArray = [...myArray];</code> <code>newArray</code>现在是<code>myArray</code>的克隆。两个阵列仍然分别存在于内存中。如果你执行像<code>newArray.push(5)</code>这样的变异， <code>myArray</code>不会改变。 <code>...</code>有效地<i>将</i> <code>myArray</code>的值<i>展开</i>到一个新数组中。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>myArray</code>中的值和字符串<code>'new value'</code>组成的新数组作为最后一个值。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是生成数组的浅表副本。也就是说，它只为一维数组提供不可变的数组操作。 </section>
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## Instructions
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<section id="instructions">添加待办事项时，使用spread运算符返回新的状态副本。 </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存储应该存在并初始化为等于<code>[Do not mutate state!]</code> 。'
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testString: 'assert((function() { const initialState = store.getState(); return ( Array.isArray(initialState) === true && initialState[0] === "Do not mutate state!"); })(), "The Redux store should exist and initialize with a state equal to <code>[Do not mutate state!]</code>.");'
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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 = [ "Do not mutate state!", "__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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- text: 应使用扩展运算符返回新状态。
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testString: 'getUserInput => assert(getUserInput("index").includes("...state"), "The spread operator should be used to return new 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 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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// 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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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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