111 lines
3.6 KiB
Markdown
111 lines
3.6 KiB
Markdown
---
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id: 5a24c314108439a4d403615b
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title: Copy an Object with Object.assign
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challengeType: 6
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isRequired: false
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forumTopicId: 301437
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localeTitle: 使用 Object.assign 拷贝对象
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---
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## Description
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<section id='description'>
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最后几个挑战适用于数组，但是当状态是<code>object</code>时，有一些方法可以帮助强制执行状态不变性。处理对象的一个方法是<code>Object.assign()</code>。<code> Object.assign()</code>获取目标对象和源对象，并将源对象中的属性映射到目标对象。任何匹配的属性都会被源对象中的属性覆盖。通常用于通过传递一个空对象作为第一个参数，然后是要用复制的对象来制作对象的浅表副本。这是一个例子：
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<code>const newObject = Object.assign({}, obj1, obj2);</code>
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这会创建<code>newObject</code>作为新的<code>object</code>，其中包含<code>obj1</code>和<code>obj2</code>中当前存在的属性。
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</section>
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## Instructions
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<section id='instructions'>
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Redux 状态和 action 被修改为处理<code>state</code>的<code>对象</code>。编辑代码以返回一个新的<code>state</code>对象，用于类型的 action<code>ONLINE</code>，它将<code>status</code>属性设置为字符串<code>online</code>。尝试使用<code>Object.assign()</code>来完成挑战。
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</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 store 应该存在并使用与第 1 行声明的<code>defaultState</code>对象相同的状态进行初始化。
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testString: 'assert((function() { const expectedState = { user: ''CamperBot'', status: ''offline'', friends: ''732,982'', community: ''freeCodeCamp'' }; const initialState = store.getState(); return DeepEqual(expectedState, initialState); })());'
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- text: <code>wakeUp</code>和<code>immutableReducer</code>都应该是函数。
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testString: assert(typeof wakeUp === 'function' && typeof immutableReducer === 'function');
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- text: dispatch 一个类型为<code>ONLINE</code>的 action 应该将状态<code>status</code>更新为<code>online</code>，并且不应该改变状态。
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testString: 'assert((function() { const initialState = store.getState(); const isFrozen = DeepFreeze(initialState); store.dispatch({type: ''ONLINE''}); const finalState = store.getState(); const expectedState = { user: ''CamperBot'', status: ''online'', friends: ''732,982'', community: ''freeCodeCamp'' }; return isFrozen && DeepEqual(finalState, expectedState); })());'
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- text: <code>Object.assign</code>应该被用于返回一个新状态。
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testString: getUserInput => assert(getUserInput('index').includes('Object.assign'));
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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 defaultState = {
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user: 'CamperBot',
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status: 'offline',
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friends: '732,982',
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community: 'freeCodeCamp'
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};
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const immutableReducer = (state = defaultState, action) => {
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switch(action.type) {
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case 'ONLINE':
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// 不要在这里改变 state 否则测试会失败。
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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 wakeUp = () => {
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return {
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type: 'ONLINE'
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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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const defaultState = {
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user: 'CamperBot',
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status: 'offline',
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friends: '732,982',
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community: 'freeCodeCamp'
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};
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const immutableReducer = (state = defaultState, action) => {
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switch(action.type) {
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case 'ONLINE':
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return Object.assign({}, state, {
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status: 'online'
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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 wakeUp = () => {
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return {
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type: 'ONLINE'
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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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</section>
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