js输出顺序

console.log('======== main task start ========');
new Promise(resolve => {
  console.log('create micro task 1');
  resolve();
}).then(() => {
  console.log('micro task 1 callback');
  setTimeout(() => {
    console.log('macro task 3 callback');
  }, 0);
})

console.log('create macro task 2');
setTimeout(() => {
  console.log('macro task 2 callback');
  new Promise(resolve => {
    console.log('create micro task 3');
    resolve();
  }).then(() => {
    console.log('micro task 3 callback');
  })
  console.log('create macro task 4');
  setTimeout(() => {
    console.log('macro task 4 callback');
  }, 0);
}, 0);

new Promise(resolve => {
  console.log('create micro task 2');
  resolve();
}).then(() => {
  console.log('micro task 2 callback');
})

console.log('======== main task end ========');

======== main task start ========
create micro task 1
create macro task 2
create micro task 2
======== main task end ========
micro task 1 callback
micro task 2 callback
macro task 2 callback
create micro task 3
create macro task 4
micro task 3 callback
macro task 3 callback
macro task 4 callback

await 表达式会暂停当前 async function 的执行，等待 Promise 处理完成。
在没有 await 的情况下执行 async 函数，它会立即执行，返回一个 Promise 对象，并且，绝不会阻塞后面的语句

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(function(resolve){
  console.log('promise1')
  resolve();
}).then(function(){
  console.log('promise2')
})
console.log('script end')

script start
async1 start
async2
promise1
script end
async1 end
promise2
setTimeout

async function t1 () {
console.log(1)
console.log(2)
new Promise( function ( resolve ) {
console.log( 'promise3' )
resolve();
} ).then( function () {
console.log( 'promise4' )
} )
await new Promise( function ( resolve ) {
console.log( 'b' )
resolve();
} ).then( function () {
console.log( 't1p' )
} )

console.log(3)
console.log(4)
new Promise( function ( resolve ) {
console.log( 'promise5' )
resolve();
} ).then( function () {
console.log( 'promise6' )
} )
}



setTimeout( function () {
console.log( 'setTimeout' )
}, 0 )

async function t2() {
console.log(5)
console.log(6)
await Promise.resolve().then(() => console.log('t2p'))
console.log(7)
console.log(8)
}

t1()
new Promise( function ( resolve ) {
console.log( 'promise1' )
resolve();
} ).then( function () {
console.log( 'promise2' )
} )
t2()

console.log('end');

1
2
promise3
b
promise1
5
6
end
promise4
t1p
promise2
t2p
3
4
promise5
7
8
promise6
setTimeout