1. Promise.resolve().then(() => {
    2.     console.log(0);
    3.     return Promise.resolve(4);
    4. }).then((res) => {
    5.     console.log(res)
    6. })
    8. Promise.resolve().then(() => {
    9.     console.log(1);
    10. }).then(() => {
    11.     console.log(2);
    12. }).then(() => {
    13.     console.log(3);
    14. }).then(() => {
    15.     console.log(5);
    16. }).then(() =>{
    17.     console.log(6);
    18. })
    20. //预想输出0 1 2 4 3 5 6
    21. //实际输入0 1 2 3 4 5 6