异步经典题

console.log('sync1')-----------------1次打印                

setTimeout(function(){
	console.log('setTimeout1')
},0)//+1----------------------------setTimeout

var promise=new Promise(function(resolve,reject){
	setTimeout(function(){
		console.log('setTimeoutPromise')
	},0)//+2-------------------------setTimeout
	console.log('promise')-----------2次打印
	resolve()
})

promise.then(()=>{-------------------------resolve
	console.log('pro_then')
	setTimeout(()=>{
		console.log('pro_timeout')
	},0)
})

setTimeout(function(){
	console.log('last_setTimeout')
},0)//+3---------------------------------setTimout

console.log('sync_2')---------------------3次打印

打印顺序
sync1
promise
sync_2

pro_then//先执行then
setTimeout1
setTimeutPromsie
last_setTimeout

pro_timeout