async函数

示例

async function getStockPriceByName(name) {
  const symbol = await getStockSymbol(name);
  const stockPrice = await getStockPrice(symbol);
  return stockPrice;
}
 
getStockPriceByName('goog').then(function (result) {
  console.log(result);
});

async函数内部return语句返回的值，会成为then方法回调函数的参数。

async function f() {
  return 'hello world';
}
 
f().then(v => console.log(v))

async函数内部抛出错误，会导致返回的 Promise 对象变为reject状态。抛出的错误对象会被catch方法回调函数接收到

async function f() {
  throw new Error('出错了');
}
 
f().then(
  v => console.log(v),
  e => console.log(e)
)

只有async函数内部的异步操作执行完，才会执行then方法指定的回调函数。

async function getTitle(url) {
  let response = await fetch(url);
  let html = await response.text();
  return html.match(/