87 lines
4.7 KiB
Markdown
87 lines
4.7 KiB
Markdown
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---
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id: 5a24c314108439a4d4036178
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title: Create a Controlled Input
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 创建受控输入
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---
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## Description
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<section id="description">您的应用程序可能在<code>state</code>和呈现的UI之间进行更复杂的交互。例如，用于文本输入的表单控件元素（例如<code>input</code>和<code>textarea</code>在用户键入时在DOM中维护它们自己的状态。使用React，您可以将此可变状态移动到React组件的<code>state</code> 。用户的输入成为应用程序<code>state</code>一部分，因此React控制该输入字段的值。通常，如果React组件具有用户可以键入的输入字段，则它将是受控输入表单。 </section>
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## Instructions
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<section id="instructions">代码编辑器具有名为<code>ControlledInput</code>的组件的骨架，以创建受控<code>input</code>元素。组件的<code>state</code>已经使用包含空字符串的<code>input</code>属性进行初始化。此值表示用户在<code>input</code>字段中键入的文本。首先，创建一个名为<code>handleChange()</code>的方法，该方法具有一个名为<code>event</code>的参数。调用该方法时，它会接收一个<code>event</code>对象，该对象包含<code>input</code>元素中的一串文本。您可以使用方法内的<code>event.target.value</code>访问此字符串。使用此新字符串更新组件<code>state</code>的<code>input</code>属性。在render方法中，在<code>h4</code>标记上方创建<code>input</code>元素。添加一个<code>value</code>属性，该属性等于组件<code>state</code>的<code>input</code>属性。然后将<code>onChange()</code>事件处理程序集添加到<code>handleChange()</code>方法。当您在输入框中键入时，该文本由<code>handleChange()</code>方法处理，设置为本地<code>state</code>的<code>input</code>属性，并在页面的<code>input</code>框中呈现为值。组件<code>state</code>是关于输入数据的单一事实来源。最后但并非最不重要的是，不要忘记在构造函数中添加必要的绑定。 </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>ControlledInput</code>应返回包含<code>input</code>和<code>p</code>标记的<code>div</code>元素。
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testString: 'assert(Enzyme.mount(React.createElement(ControlledInput)).find("div").children().find("input").length === 1 && Enzyme.mount(React.createElement(ControlledInput)).find("div").children().find("p").length === 1, "<code>ControlledInput</code> should return a <code>div</code> element which contains an <code>input</code> and a <code>p</code> tag.");'
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- text: <code>ControlledInput</code>的状态应该初始化， <code>input</code>属性设置为空字符串。
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testString: 'assert.strictEqual(Enzyme.mount(React.createElement(ControlledInput)).state("input"), "", "The state of <code>ControlledInput</code> should initialize with an <code>input</code> property set to an empty string.");'
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- text: 输入input元素应更新输入的状态和值， <code>p</code>元素应在键入时呈现此状态。
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(ControlledInput)); const _1 = () => { mockedComponent.setState({ input: "" }); return waitForIt(() => mockedComponent.state("input"))}; const _2 = () => { mockedComponent.find("input").simulate("change", { target: { value: "TestInput" }}); return waitForIt(() => ({ state: mockedComponent.state("input"), text: mockedComponent.find("p").text(), inputVal: mockedComponent.find("input").props().value }))}; const before = await _1(); const after = await _2(); assert(before === "" && after.state === "TestInput" && after.text === "TestInput" && after.inputVal === "TestInput", "Typing in the input element should update the state and the value of the input, and the <code>p</code> element should render this state as you type."); }; '
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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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class ControlledInput extends React.Component {
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constructor(props) {
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super(props);
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this.state = {
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input: "
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};
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// change code below this line
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// change code above this line
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}
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// change code below this line
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// change code above this line
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render() {
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return (
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<div>
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{ /* change code below this line */}
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{ /* change code above this line */}
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<h4>Controlled Input:</h4>
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<p>{this.state.input}</p>
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</div>
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);
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}
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};
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```
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</div>
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### After Test
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<div id='jsx-teardown'>
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```js
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console.info('after the test');
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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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