async function fn1(){
console.log(3)
await fn2()
//异步
console.log(4)
}
async function fn2(){
console.log(5)
await fn3()
// 异步
console.log(6)
}
async function fn3(){
console.log(7)
}
console.log(1)
fn1()
console.log(2)
fn2()
//1 3 5 7 2 5 7 6 6 4