2021-04-30 17:55:17 +08:00
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2021-05-23 18:51:05 +08:00
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## Promise 的常用API分类
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2021-04-30 17:55:17 +08:00
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2021-05-23 18:51:05 +08:00
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### Promise的实例方法
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2021-04-30 17:55:17 +08:00
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2021-05-23 18:51:05 +08:00
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**实例方法**：我们需要先 new 一个 promise实例对象，然后通过 promise对象去调用 `then`、`catch`、`finally`方法。这几个方法就是 Promise 的实例方法。
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2021-04-30 17:55:17 +08:00
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2021-05-23 18:51:05 +08:00
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具体来说，Promise 的自带API 提供了如下实例方法：
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2021-04-30 17:55:17 +08:00
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- promise.then()：获取异步任务的正常结果。
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- promise.catch()：获取异步任务的异常结果。
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- promise.finaly()：异步任务无论成功与否，都会执行。
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2021-05-23 18:51:05 +08:00
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### Promise的静态方法
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**静态方法**：可以直接通过大写的`Promise.xxx`调用的方法。这里的`xxx`就称之为静态方法。
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具体来说，Promise 的自带API 提供了如下静态方法：
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- `Promise.resolve()`
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- `Promise.reject()`
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- `Promsie.all()`
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- `Promise.race`
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前面的几篇文章，讲的都是 Promise的**实例方法**；今天这篇文章，我们来详细讲一下 Promise的**静态方法**。
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2021-04-30 17:55:17 +08:00
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## Promise 的常用 API：对象方法【重要】
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Promise 自带的 API 提供了如下对象方法：
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- Promise.all()：并发处理多个异步任务，所有任务都执行成功，才能得到结果。
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- Promise.race(): 并发处理多个异步任务，只要有一个任务执行成功，就能得到结果。
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下面来详细介绍。
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### Promise.all() 代码举例
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代码举例：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<title>Document</title>
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</head>
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<body>
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<script type="text/javascript">
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/*
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封装 Promise 接口调用
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*/
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function queryData(url) {
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return new Promise((resolve, reject) => {
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var xhr = new XMLHttpRequest();
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xhr.onreadystatechange = function () {
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if (xhr.readyState != 4) return;
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if (xhr.readyState == 4 && xhr.status == 200) {
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// 处理正常结果
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resolve(xhr.responseText);
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} else {
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// 处理异常结果
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reject('服务器错误');
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}
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};
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xhr.open('get', url);
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xhr.send(null);
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});
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}
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var promise1 = queryData('http://localhost:3000/api1');
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var promise2 = queryData('http://localhost:3000/api2');
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var promise3 = queryData('http://localhost:3000/api3');
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Promise.all([promise1, promise2, promise3]).then((result) => {
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console.log(result);
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});
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</script>
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</body>
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</html>
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```
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### Promise.race() 代码举例
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代码举例：
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```html
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<title>Document</title>
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</head>
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<body>
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<script type="text/javascript">
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/*
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封装 Promise 接口调用
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*/
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function queryData(url) {
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return new Promise((resolve, reject) => {
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var xhr = new XMLHttpRequest();
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xhr.onreadystatechange = function () {
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if (xhr.readyState != 4) return;
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if (xhr.readyState == 4 && xhr.status == 200) {
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// 处理正常结果
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resolve(xhr.responseText);
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} else {
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// 处理异常结果
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reject('服务器错误');
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}
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};
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xhr.open('get', url);
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xhr.send(null);
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});
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}
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var promise1 = queryData('http://localhost:3000/api1');
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var promise2 = queryData('http://localhost:3000/api2');
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var promise3 = queryData('http://localhost:3000/api3');
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Promise.race([promise1, promise2, promise3]).then((result) => {
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console.log(result);
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});
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</script>
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</body>
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</html>
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```
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