82 lines
2.2 KiB
Markdown
82 lines
2.2 KiB
Markdown
---
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id: 5cdafbc32913098997531680
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title: 通过 resolve 和 reject 完成 Promise
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challengeType: 1
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forumTopicId: 301196
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dashedName: complete-a-promise-with-resolve-and-reject
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---
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# --description--
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promise 有三个状态：`pending`、`fulfilled` 和 `rejected`。上一个挑战里创建的 promise 一直阻塞在 `pending` 状态里，因为没有调用 promise 的完成方法。promise 提供的 `resolve` 和 `reject` 参数就是用来结束 promise 的。promise 成功时调用 `resolve`，promise 执行失败时调用 `reject`，这两个方法接收一个参数，如下所示。
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```js
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const myPromise = new Promise((resolve, reject) => {
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if(condition here) {
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resolve("Promise was fulfilled");
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} else {
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reject("Promise was rejected");
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}
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});
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```
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上面的例子使用字符串做为函数的参数，也可以是任意类型，通常会是对象，里面可能是将要放到页面或其它地方的数据。
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# --instructions--
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使 promise 可以处理成功和失败情况。如果 `responseFromServer` 是 `true`，调用 `resolve` 方法使 promise 成功。给 `resolve` 传递值为 `We got the data` 的字符串。如果 `responseFromServer` 是 `false`， 使用 `reject` 方法并传入值为 `Data not received` 的字符串。
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# --hints--
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当 `if` 条件是 `true` 时应该执行 `resolve`。
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```js
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assert(
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removeJSComments(code).match(
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/if\s*\(\s*responseFromServer\s*\)\s*{\s*resolve\s*\(\s*('|"|`)We got the data\1\s*\)(\s*|\s*;\s*)}/g
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)
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);
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```
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当 `if` 条件是 `false` 时应该执行 `reject`。
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```js
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assert(
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removeJSComments(code).match(
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/}\s*else\s*{\s*reject\s*\(\s*('|"|`)Data not received\1\s*\)(\s*|\s*;\s*)}/g
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)
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);
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```
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# --seed--
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## --seed-contents--
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```js
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const makeServerRequest = new Promise((resolve, reject) => {
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// responseFromServer represents a response from a server
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let responseFromServer;
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if(responseFromServer) {
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// Change this line
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} else {
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// Change this line
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}
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});
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```
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# --solutions--
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```js
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const makeServerRequest = new Promise((resolve, reject) => {
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// responseFromServer represents a response from a server
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let responseFromServer;
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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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```
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