同步、异步、回调函数面试经典问题

1、首先需要记住的是这么一句话 

       同步先行==》异步靠边=》回调垫底

<script>
        var a = new Promise(function () {
            console.log(1);
            setTimeout(() => consoel.log(2), 0);
            console.log(3);
            console.log(4);
            resolve(true);
        })
        a.then(v => {
            console.log(8)
        });
        var b = new Promise(function () {
             console.log(5);
             setTimeout(() => console.log(6), 0);
        });
        console.log(7);
  </script>