SOURCE

> script 开始
> async1 开始
> async2
> script结束
> async1结束

async function async1(){
    console.log("async1 开始");
    await async2();
    console.log("async1结束");
}
async function async2(){
    console.log("async2");
}
console.log("script 开始");
async1();
console.log("script结束")