1
function a() {
2
    console.log("1");
3
    Promise.resolve().then(() => {
4
        console.log("2");
5
    });
6
}
7
setTimeout(function () {
8
    console.log("3");
9
    Promise.resolve().then(a);
10
}, 0);
11

12
Promise.resolve().then(function () {
13
    console.log("4");
14
});
15

16
console.log("5");