87 lines
4.4 KiB
Markdown
87 lines
4.4 KiB
Markdown
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---
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id: 5a24c314108439a4d4036185
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title: Use && for a More Concise Conditional
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 使用&&获得更简洁的条件
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---
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## Description
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<section id="description"> if / else语句在最后一次挑战中起作用，但是有一种更简洁的方法来实现相同的结果。想象一下，您正在跟踪组件中的多个条件，并且您希望根据这些条件中的每个条件呈现不同的元素。如果你写了很多<code>else if</code>语句来返回略有不同的UI，你可能会重复代码，这会留下错误的余地。相反，您可以使用<code>&&</code> logical运算符以更简洁的方式执行条件逻辑。这是可能的，因为您要检查条件是否为<code>true</code> ，如果是，则返回一些标记。下面是一个示例： <code>{condition && <p>markup</p>}</code>如果<code>condition</code>为<code>true</code> ，则返回标记。如果条件为<code>false</code> ，则在评估<code>condition</code>后操作将立即返回<code>false</code>并且不返回任何内容。您可以直接在JSX中包含这些语句，并在每个语句之后写入<code>&&</code>多个条件串在一起。这允许您在<code>render()</code>方法中处理更复杂的条件逻辑，而无需重复大量代码。 </section>
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## Instructions
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<section id="instructions">再次解决前面的示例，因此<code>h1</code>仅在<code>display</code>为<code>true</code>呈现，但使用<code>&&</code> logical运算符而不是<code>if/else</code>语句。 </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>MyComponent</code>应该存在并呈现。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); return mockedComponent.find("MyComponent").length; })(), "<code>MyComponent</code> should exist and render.");'
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- text: 当<code>display</code>设置为<code>true</code> ，应该渲染<code>div</code> ， <code>button</code>和<code>h1</code> 。
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const state_1 = () => { mockedComponent.setState({display: true}); return waitForIt(() => mockedComponent )}; const updated = await state_1(); assert(updated.find("div").length === 1 && updated.find("div").children().length === 2 && updated.find("button").length === 1 && updated.find("h1").length === 1, "When <code>display</code> is set to <code>true</code>, a <code>div</code>, <code>button</code>, and <code>h1</code> should render."); }; '
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- text: 当<code>display</code>设置为<code>false</code> ，只应呈现<code>div</code>和<code>button</code> 。
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testString: 'async () => { const waitForIt = (fn) => new Promise((resolve, reject) => setTimeout(() => resolve(fn()), 250)); const mockedComponent = Enzyme.mount(React.createElement(MyComponent)); const state_1 = () => { mockedComponent.setState({display: false}); return waitForIt(() => mockedComponent )}; const updated = await state_1(); assert(updated.find("div").length === 1 && updated.find("div").children().length === 1 && updated.find("button").length === 1 && updated.find("h1").length === 0, "When <code>display</code> is set to <code>false</code>, only a <code>div</code> and <code>button</code> should render."); }; '
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- text: render方法应该使用&& logical运算符来检查this.state.display的条件。
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testString: 'getUserInput => assert(getUserInput("index").includes("&&"), "The render method should use the && logical operator to check the condition of this.state.display.");'
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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 MyComponent 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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display: true
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}
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this.toggleDisplay = this.toggleDisplay.bind(this);
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}
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toggleDisplay() {
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this.setState({
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display: !this.state.display
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});
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}
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render() {
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// change code below this line
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return (
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<div>
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<button onClick={this.toggleDisplay}>Toggle Display</button>
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<h1>Displayed!</h1>
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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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