68 lines
2.1 KiB
Markdown
68 lines
2.1 KiB
Markdown
---
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id: 5a24c314108439a4d403616b
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title: Use Default Props
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challengeType: 6
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isRequired: false
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videoUrl: ''
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localeTitle: 使用默认道具
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---
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## Description
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<section id="description"> React还有一个设置默认道具的选项。您可以将默认道具分配给组件作为组件本身的属性，如果需要，React会分配默认支柱。如果没有显式提供值，这允许您指定prop值应该是什么。例如，如果您声明<code>MyComponent.defaultProps = { location: 'San Francisco' }</code> ，则您已定义了设置为<code>San Francisco</code>字符串的位置道具，除非您另行指定。如果道具未定义，则React会指定默认道具，但如果您将<code>null</code>作为道具的值传递，则它将保持为<code>null</code> 。 </section>
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## Instructions
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<section id="instructions">代码编辑器显示<code>ShoppingCart</code>组件。在此组件上定义默认道具，指定值为<code>0</code>的道具<code>items</code> 。 </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>ShoppingCart</code>组件应该呈现。
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart)); return mockedComponent.find("ShoppingCart").length === 1; })(), "The <code>ShoppingCart</code> component should render.");'
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- text: '<code>ShoppingCart</code>组件应具有<code>{ items: 0 }</code>的默认支柱。'
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testString: 'assert((function() { const mockedComponent = Enzyme.mount(React.createElement(ShoppingCart)); mockedComponent.setProps({items: undefined}); return mockedComponent.find("ShoppingCart").props().items === 0; })(), "The <code>ShoppingCart</code> component should have a default prop of <code>{ items: 0 }</code>.");'
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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 ShoppingCart = (props) => {
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return (
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<div>
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<h1>Shopping Cart Component</h1>
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</div>
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)
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};
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// change code below this line
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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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