62 lines
2.5 KiB
Markdown
62 lines
2.5 KiB
Markdown
---
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id: 587d7fb1367417b2b2512bf4
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challengeType: 2
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forumTopicId: 301510
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title: 使用链中间件来创建时间服务器
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---
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## Description
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<section id='description'>
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使用<code>app.METHOD(path, middlewareFunction)</code>可以将中间件挂载到指定的路由。中间件也可以在路由定义中链接。
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请看以下示例:
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```js
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app.get('/user', function(req, res, next) {
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req.user = getTheUserSync(); // Hypothetical synchronous operation
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next();
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}, function(req, res) {
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res.send(req.user);
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});
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```
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此方法可用于将服务操作拆分为较小的单元。这样可以让应用拥有更好的结构,以便于在不同的位置上复用代码。此方法还可用于对数据执行某些验证。在每一个中间件堆栈中,你都可以阻止当前链的执行,并将控制权传递给专门设计用于处理错误的函数。或者你可以将控制权传递给下一个匹配的路径,以处理特殊情况。我们将在高级 Express 章节中看到。
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</section>
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## Instructions
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<section id='instructions'>
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在路由<code>app.get('/now', ...)</code>链中,在中间件函数中,你应该在<code>req.time</code>里将当前时间添加到请求对象中。你可以使用<code>new Date().toString()</code>。在处理函数中,使用<code>{time: req.time}</code>结构的 JSON 对象来响应。
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提示: 如果不链接中间件,测试将不能通过。如果将中间件函数挂载在其他地方,即使输出结果正确,测试也会失败。
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</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: 路由 /now 应该已经挂载了中间件
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testString: 'getUserInput => $.get(getUserInput(''url'') + ''/_api/chain-middleware-time'').then(data => { assert.equal(data.stackLength, 2, ''"/now" route has no mounted middleware''); }, xhr => { throw new Error(xhr.responseText); })'
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- text: 路由 /now 应该返回一个从现在开始 +/-20 秒的时间
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testString: 'getUserInput => $.get(getUserInput(''url'') + ''/_api/chain-middleware-time'').then(data => { var now = new Date(); assert.isAtMost(Math.abs(new Date(data.time) - now), 20000, ''the returned time is not between +- 20 secs from now''); }, xhr => { throw new Error(xhr.responseText); })'
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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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</section>
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## Solution
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<section id='solution'>
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```js
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/**
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Backend challenges don't need solutions,
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because they would need to be tested against a full working project.
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Please check our contributing guidelines to learn more.
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*/
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```
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</section>
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