60 lines
1.7 KiB
Markdown
60 lines
1.7 KiB
Markdown
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---
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id: 587d7b8c367417b2b2512b58
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title: Create an Export Fallback with export default
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challengeType: 1
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videoUrl: ''
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localeTitle: 使用导出默认值创建导出回退
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---
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## Description
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<section id="description">在<code>export</code>课程中，您了解了称为<dfn>命名导出</dfn>的语法。这使您可以使多个函数和变量可用于其他文件。您需要知道另一种<code>export</code>语法，称为<dfn>导出默认值</dfn> 。通常，如果只从文件导出一个值，您将使用此语法。它还用于为文件或模块创建回退值。以下是<code>export default</code>的快速示例： <blockquote> export default function add（x，y）{ <br>返回x + y; <br> } </blockquote>注意：由于<code>export default</code>用于声明模块或文件的回退值，因此每个模块或文件中只能有一个值作为默认导出。此外，您不能将<code>export default</code>用于<code>var</code> ， <code>let</code>或<code>const</code> </section>
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## Instructions
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<section id="instructions">以下函数应该是模块的回退值。请添加必要的代码。 </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: 适当使用<code>export</code>回落。
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testString: 'getUserInput => assert(getUserInput("index").match(/export\s+default\s+function\s+subtract\(x,y\)\s+{return\s+x\s-\s+y;}/g), "Proper used of <code>export</code> fallback.");'
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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='js-seed'>
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```js
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"use strict";
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function subtract(x,y) {return x - y;}
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```
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</div>
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### Before Test
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<div id='js-setup'>
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```js
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window.exports = function(){};
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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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