103 lines
2.4 KiB
Markdown
103 lines
2.4 KiB
Markdown
---
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id: 5cdafbe72913098997531682
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challengeType: 1
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forumTopicId: 301204
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title: 在 catch 中处理 Promise 失败的情况
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---
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## Description
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<section id='description'>
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当 promise 失败时会调用 <code>catch</code> 方法。当 promise 的 <code>reject</code> 方法执行时会直接调用。用法如下：
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```js
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myPromise.catch(error => {
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// do something with the error.
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});
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```
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<code>error</code> 是传入 <code>reject</code> 方法的参数。
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<strong>注意：</strong> <code>then</code> 和 <code>catch</code> 方法可以在 promise 后面链式调用。
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</section>
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## Instructions
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<section id='instructions'>
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给 promise 添加 <code>catch</code> 方法。用 <code>error</code> 做为回调函数的参数并把 <code>error</code> 打印到控制台。
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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: 应该在 promise 上调用 <code>catch</code> 方法。
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testString: assert(codeWithoutSpaces.match(/(makeServerRequest|\))\.catch\(/g));
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- text: <code>catch</code> 方法应该有一个回调函数，函数参数为<code>error</code>。
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testString: assert(errorIsParameter);
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- text: 应该打印<code>error</code>到控制台。
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testString: assert(errorIsParameter && codeWithoutSpaces.match(/\.catch\(.*?error.*?console.log\(error\).*?\)/));
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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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const makeServerRequest = new Promise((resolve, reject) => {
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// responseFromServer is set to false to represent an unsuccessful response from a server
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let responseFromServer = false;
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if(responseFromServer) {
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resolve("We got the data");
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} else {
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reject("Data not received");
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}
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});
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makeServerRequest.then(result => {
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console.log(result);
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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='js-teardown'>
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```js
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const codeWithoutSpaces = code.replace(/\s/g, '');
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const errorIsParameter = /\.catch\((function\(error\){|error|\(error\)=>)/.test(codeWithoutSpaces);
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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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const makeServerRequest = new Promise((resolve, reject) => {
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// responseFromServer is set to false to represent an unsuccessful response from a server
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let responseFromServer = false;
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if(responseFromServer) {
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resolve("We got the data");
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} else {
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reject("Data not received");
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}
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});
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makeServerRequest.then(result => {
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console.log(result);
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});
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makeServerRequest.catch(error => {
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console.log(error);
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});
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```
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</section>
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