宏任务与微任务

老规矩，先放两道题目，先看看会有什么结果输出，然后我们一起研究为什么

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
undefined
setTimeout/*

new Promise(function(resolve){
   console.log('2');
}).then(function(){
   console.log('3')
});

console.log('4');

//2
//4

new Promise(function(resolve){
    console.log('2');
    resolve();
}).then(function(){
    console.log('3')
});

console.log('4');

//2
//4
//3

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();
script start
async1 start
async2
async1 end
Promise {<resolved>: undefined}
setTimeout*/

未完，待续...