SOURCE

async function async1(){
    console.log('async1 start')
    await async2()
    console.log('async1 end')
  }
// 等价于
// async function async1(){
//     console.log('async1 start')
//     return async2().then(result => {
//       console.log('async1 end')
//     })
//   }
async function async2(){
    console.log('async2')
  }
console.log('script start')
setTimeout(function(){
    console.log('setTimeout') 
 },0)  
async1();
new Promise(function(resolve){
    console.log('promise1')
    resolve();
 }).then(function(){
    console.log('promise2')
})
console.log('script end')