61460c8601
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89 lines
3.6 KiB
Markdown
89 lines
3.6 KiB
Markdown
---
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id: 5a24c314108439a4d4036184
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title: Render with an If-Else Condition
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 使用If-Else条件渲染
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---
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## Description
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<section id="description">使用JavaScript控制渲染视图的另一个应用是将呈现的元素绑定到条件。当条件为真时，一个视图呈现。当它是假的时，它是一个不同的观点。您可以使用React组件的<code>render()</code>方法中的标准<code>if/else</code>语句执行此操作。 </section>
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## Instructions
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<section id="instructions"> MyComponent在其状态中包含一个<code>boolean</code> ，用于跟踪是否要在UI中显示某个元素。该<code>button</code>切换此值的状态。目前，它每次都呈现相同的UI。使用<code>if/else</code>语句重写<code>render()</code>方法，以便如果<code>display</code>为<code>true</code> ，则返回当前标记。否则，返回没有<code>h1</code>元素的标记。 <strong>注意：</strong>您必须编写<code>if/else</code>以传递测试。使用三元运算符不会通过此处。 </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 === 1; })());
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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(mockedComponent.find(''div'').length === 1 && mockedComponent.find(''div'').children().length === 2 && mockedComponent.find(''button'').length === 1 && mockedComponent.find(''h1'').length === 1); }; '
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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(mockedComponent.find(''div'').length === 1 && mockedComponent.find(''div'').children().length === 1 && mockedComponent.find(''button'').length === 1 && mockedComponent.find(''h1'').length === 0); }; '
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- text: render方法应使用<code>if/else</code>语句来检查<code>this.state.display</code>的条件。
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testString: getUserInput => assert(getUserInput('index').includes('if') && getUserInput('index').includes('else'));
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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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