104 lines
4.9 KiB
Markdown
104 lines
4.9 KiB
Markdown
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---
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id: 5a24c314108439a4d4036156
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title: Use Middleware to Handle Asynchronous Actions
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 使用中间件处理异步操作
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---
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## Description
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<section id="description">到目前为止，这些挑战已经避免讨论异步操作，但它们是Web开发中不可避免的一部分。在某些时候，您需要在Redux应用程序中调用异步端点，那么如何处理这些类型的请求？ Redux提供专门为此目的而设计的中间件，称为Redux Thunk中间件。以下是如何在Redux中使用它的简要说明。要包含Redux Thunk中间件，请将其作为参数传递给<code>Redux.applyMiddleware()</code> 。然后，此语句作为<code>createStore()</code>函数的第二个可选参数提供。看一下编辑器底部的代码，看看这个。然后，要创建异步操作，您将在动作创建器中返回一个函数，该函数将<code>dispatch</code>作为参数。在此函数中，您可以分派操作并执行异步请求。在此示例中，使用<code>setTimeout()</code>调用模拟异步请求。在启动任何异步行为之前调度操作是很常见的，这样您的应用程序状态就知道正在请求某些数据（例如，此状态可能会显示加载图标）。然后，一旦收到数据，就会发送另一个操作，该操作将数据作为有效负载以及操作完成的信息。请记住，您将<code>dispatch</code>作为参数传递给此特殊操作创建者。这是您用于分派操作的方法，您只需将操作直接传递给调度，中间件就可以处理其余操作。 </section>
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## Instructions
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<section id="instructions">在<code>handleAsync()</code>动作创建器中写入两个调度。调度<code>requestingData()</code>在之前<code>setTimeout()</code>模拟API调用）。然后，在收到（假装）数据后，调度<code>receivedData()</code>操作，传入此数据。现在您知道如何在Redux中处理异步操作。其他一切继续像以前一样。 </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: <code>requestingData</code>操作创建者应返回类型等于<code>REQUESTING_DATA</code>值的对象。
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testString: 'assert(requestingData().type === REQUESTING_DATA, "The <code>requestingData</code> action creator should return an object of type equal to the value of <code>REQUESTING_DATA</code>.");'
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- text: <code>receivedData</code>操作创建者应返回类型等于<code>RECEIVED_DATA</code>值的对象。
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testString: 'assert(receivedData("data").type === RECEIVED_DATA, "The <code>receivedData</code> action creator should return an object of type equal to the value of <code>RECEIVED_DATA</code>.");'
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- text: <code>asyncDataReducer</code>应该是一个函数。
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testString: 'assert(typeof asyncDataReducer === "function", "<code>asyncDataReducer</code> should be a function.");'
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- text: 调度requestedData操作创建者应该将获取的store <code>state</code>属性更新为<code>true</code> 。
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testString: 'assert((function() { const initialState = store.getState(); store.dispatch(requestingData()); const reqState = store.getState(); return initialState.fetching === false && reqState.fetching === true })(), "Dispatching the requestingData action creator should update the store <code>state</code> property of fetching to <code>true</code>.");'
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- text: 调度<code>handleAsync</code>应调度数据请求操作，然后在延迟后调度接收的数据操作。
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testString: 'assert((function() { const noWhiteSpace = handleAsync.toString().replace(/\s/g,""); return noWhiteSpace.includes("dispatch(requestingData())") === true && noWhiteSpace.includes("dispatch(receivedData(data))") === true })(), "Dispatching <code>handleAsync</code> should dispatch the data request action and then dispatch the received data action after a delay.");'
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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 REQUESTING_DATA = 'REQUESTING_DATA'
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const RECEIVED_DATA = 'RECEIVED_DATA'
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const requestingData = () => { return {type: REQUESTING_DATA} }
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const receivedData = (data) => { return {type: RECEIVED_DATA, users: data.users} }
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const handleAsync = () => {
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return function(dispatch) {
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// dispatch request action here
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setTimeout(function() {
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let data = {
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users: ['Jeff', 'William', 'Alice']
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}
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// dispatch received data action here
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}, 2500);
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}
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};
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const defaultState = {
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fetching: false,
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users: []
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};
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const asyncDataReducer = (state = defaultState, action) => {
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switch(action.type) {
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case REQUESTING_DATA:
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return {
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fetching: true,
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users: []
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}
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case RECEIVED_DATA:
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return {
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fetching: false,
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users: action.users
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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 store = Redux.createStore(
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asyncDataReducer,
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Redux.applyMiddleware(ReduxThunk.default)
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);
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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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