async异步函数的执行顺序

 1 async function async1(){
 2     console.log('async1 start') //2
 3     await async2()
 4     //await async2()后面的内容可以看做是callback里得内容即是异步
 5     //类似eventloop,settimeout
 6     //Promise.resolve().then(()=>{console.log(async1 end)})
 7     console.log('async1 end') //5
 8 }
 9
10 async function async2(){
11     console.log('async2') //3
12 }
13
14 console.log('script start') //1
15 async1()
16 console.log('script end') //4

变体

 1 async function async1(){
 2     console.log('async1 start') //2
 3     await async2()
 4     //后面都是异步回调callback的内容
 5         console.log('async1 end') //4
 6         await async3()
 7             console.log('async2 end') //6
 8 }
 9
10 async function async2(){
11     console.log('async2') //3
12 }
13
14 async function async3(){
15     console.log('async3') //5
16 }
17
18 console.log('script start') //1
19 async1()
20 console.log('script end') //4

 异步函数 返回的是一个promise  内部await相当于then,await后面的是异步回调内容