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 promise chaining。 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。

让我们用一个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!