虽然 async/await 语法糖让异步代码更易读和维护，但在某些场景下，直接使用 Promise 会更合适，以下是一些具体情况：1. 旧代码库或低版本环境场景描述：当你维护的是一个较旧的 JavaScript 项目，或者项目需要兼容不支持 async/await 的旧版本浏览器（如 Internet Explorer）时，Promise 是更好的选择。因为 async/await 是 ES2017 引入的特性，旧环境可能无法识别。示例：假设你需要在一个旧项目中实现一个异步的网络请求功能，由于项目要兼容旧浏览器，只能使用 Promise。javascriptfunction makeRequest() {
return new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.example.com/data', true);
xhr.onreadystatechange = function () {
if (xhr.readyState === 4) {
if (xhr.status === 200) {
resolve(xhr.responseText);
} else {
reject(new Error('Request failed'));
}
}
};
xhr.send();
});}
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makeRequest()
.then(data => console.log(data))
.catch(error => console.error(error));- 并发操作管理场景描述：当需要同时处理多个异步操作，并且对这些操作的并发控制有较高要求时，Promise 提供的一些静态方法（如 Promise.all、Promise.race、Promise.allSettled 等）能更方便地管理并发。示例：你要同时发起多个网络请求，并且希望在所有请求都完成后再进行后续处理，就可以使用 Promise.all。javascriptfunction fetchData1() {
return fetch('https://api.example.com/data1');
}
function fetchData2() {
return fetch('https://api.example.com/data2');}
Promise.all([fetchData1(), fetchData2()])
.then(responses => Promise.all(responses.map(response => response.json())))
.then(data => console.log(data))
.catch(error => console.error(error));- 回调地狱不太复杂的情况场景描述：如果异步操作嵌套的层级并不深，使用 Promise 的 then 链来处理异步逻辑会更加简洁直接，不需要额外创建 async 函数。示例：有两个简单的异步操作，依次执行，使用 Promise 的 then 链就足够清晰。javascriptfunction asyncTask1() {
return new Promise(resolve => setTimeout(() => resolve('Task 1 completed'), 1000));
}
function asyncTask2() {
return new Promise(resolve => setTimeout(() => resolve('Task 2 completed'), 1000));}
asyncTask1()
.then(result1 => {
console.log(result1);
return asyncTask2();
})
.then(result2 => console.log(result2))
.catch(error => console.error(error));- 动态创建异步流程场景描述：当需要根据运行时的条件动态创建和管理异步操作链时，Promise 的灵活性更高。因为可以在运行时动态添加或移除 then 方法。示例：根据用户输入的条件决定是否执行某个额外的异步操作。javascriptfunction asyncTask() {
return new Promise(resolve => setTimeout(() => resolve('Base task completed'), 1000));
}
function extraTask() {
return new Promise(resolve => setTimeout(() => resolve('Extra task completed'), 1000));}
const shouldRunExtraTask = true; // 假设根据用户输入判断
let promiseChain = asyncTask();
if (shouldRunExtraTask) {
promiseChain = promiseChain.then(result => {
console.log(result);
return extraTask();
});}
promiseChain
.then(finalResult => console.log(finalResult))
.catch(error => console.error(error));
在这些场景下，优先使用 Promise 可以更好地满足项目的需求和特点。