async await执行顺序问题

async function async1(){
console.log('async1 start')
await async2()
console.log('async1 end')
}
async function async2(){
console.log('async2')
}
console.log('script start')
setTimeout(function(){
console.log('setTimeout')
}, 0)
async1()
new Promise(resolve => {
console.log('promise0')
resolve()
})
.then(()=>{
console.log('promise1')
})
.then(()=>{
console.log('promise2')
})
console.log('script end')



输出结果：
script start =>

async1 start =>

async2 =>

promise0 =>

script end =>

promise1 => promise2 =>

async1 end =>

setTimeout