AsyncAwait

const aaa = () => {
  return new Promise((resolve) => {
    resolve(1122);
  });
};
const bbb = async () => {
  const res = await aaa();
  console.log(res);
};
bbb();

async 创建一个异步函数，await 只能在异步函数的代码块中工作

基本用法

// 查询二级文章分类
static async get_category(ctx){   // async声明这是一个async函数
  const data = await CategoryModel.find();  // await获取异步结果
  if(!data) return ctx.error({msg: "暂无数据"});
  return ctx.success({data});
}

var hello = async () => {
  let response = await new Promise((resolve) => {
    setTimeout(() => resolve("aaaa"), 2000)
  })
    .then(res => {
      console.log("6: ", res)
      return res
    })
  console.log("9: ", 111)
  return response
}
hello().then(res => console.log("12: ", res));
// 依次打印为
6:  aaaa
9:  111 -》等6打印才走 9
12:  aaaa

在 fetch 里的用法

没有 async 的时候

fetch("coffee.jpg")
  .then((response) => response.blob())
  .then((myBlob) => {
    // 获取到，对DOM做处理
    let objectURL = URL.createObjectURL(myBlob);
    let image = document.createElement("img");
    image.src = objectURL;
    document.body.appendChild(image);
  })
  .catch((e) => {
    console.log(e.message);
  });

用 async 改写

async function myFetch() {
  let respone = await fetch("coffee.jpg");
  let myBlob = await response.blob();

  let objectURL = URL.createObjectURL(myBlob);
  let image = document.createElement("img");
  image.src = objectURL;
  document.body.appendChild(image);
}
myFetch().catch((e) => {
  console.log(e.message);
});

async  function (){
  awiat something
  dosomething
  return sth
}.then(res).catch(e)
// 可以return 点式应用