SOURCE

async function fn1 (){
    console.log(1)
    await fn2()
    console.log(2) // 阻塞
}

async function fn2 (){
    await fn3 ()
    console.log('fn2')
}
async function fn3 (){
    await console.log('fn3')
}
async function fn4 (){
    await console.log(4)
    console.log('fn4')
}

fn4 ()

fn1()

new Promise((resolve)=>{
    console.log('promise')
    resolve()
}).then(()=>{
    console.log('then1')
})

new Promise((resolve)=>{
    resolve()
}).then(()=>{
    console.log('then2')
})

setTimeout(()=>{
    console.log('setTimeout')
})

console.log(3)

//同步
4
1
fn3
//promise 
3

//微任务
//.then
fn4 
//.then.then  await fn()，会发生阻塞,先执行async外的代码，结果顺序为 fn->2
2   
fn2 
//then1
//then2



//宏任务
setTimeout