异步/等待
与 promise 相比，async/await 是一种更新的异步代码编写方式。 async/await 的主要优点是提高了可读性并避免了承诺链。 promise 可能会变得很长、难以阅读，并且可能包含难以调试的深层嵌套回调。
例子
回想一下我们之前的获取。
fetch('https://jsonplaceholder.typicode.com/todos/1')
.then(response => response.json())
.then(data => console.log(data))
.catch(error => console.error('error:', error))
.finally(() => console.log('all done'));
使用 async/await，代码可以重构为如下所示：
async function fetchdata() {
try {
const response = await fetch('https://jsonplaceholder.typicode.com/todos/1');
const data = await response.json();
console.log(data);
} catch (error) {
console.error('error:', error);
} finally {
console.log('all done');
}
}
fetchdata();
虽然可能多了几行代码，但这个版本更容易阅读，因为它类似于普通的同步函数。此外，如果 .then() 语句内的函数更复杂，则可读性和可调试性将受到更大的影响。 async/await 示例更加清晰。
示例 2：从餐厅订餐
async/await 的结构
async/await 函数有两个基本部分：async 和await。 async 关键字加在函数声明前，await 用于异步任务开始时。
让我们以从餐厅点餐的例子来说明这一点：
// simulate the order process with async/await
async function foodorder() {
console.log("ordering food...");
await new promise(resolve => settimeout(resolve, 2000)); // wait 2 seconds for food to be prepared
return "your food is ready!";
}
// simulate the eating process
function eatfood(order) {
console.log(order); // this logs "your food is ready!"
console.log("enjoying the meal!");
}
// simulate continuing the conversation
function continueconversation() {
console.log("while waiting, you continue chatting with friends...");
}
async function orderfood() {
console.log("you've arrived at the restaurant.");
const order = await foodorder(); // place the order and wait for it to be ready
continueconversation(); // chat while waiting
eatfood(order); // eat the food once it arrives
}
orderfood();
输出将是
You've arrived at the restaurant. Ordering food... While waiting, you continue chatting with friends... Your food is ready! Enjoying the meal!
