打印什么

  1. async function async1() {
  2.     console.log("async1 start");
  3.     await  async2();
  4.     console.log("async1 end");
  5. }
  6. async  function async2() {
  7.     console.log( 'async2');
  8. }
  9. console.log("script start");
  10. setTimeout(function () {
  11.     console.log("settimeout");
  12. });
  13. async1()
  14. new Promise(function (resolve) {
  15.     console.log("promise1");
  16.     resolve();
  17. }).then(function () {
  18.     console.log("promise2");
  19. });
  20. setImmediate(()=>{
  21.     console.log("setImmediate")
  22. })
  23. process.nextTick(()=>{
  24.     console.log("process")
  25. })
  26. console.log('script end');

第一轮：

current task：”script start”，”async1 start”，’async2’，”promise1”，“script end” micro task queue：[async,promise.then,process] macro task queue：[setTimeout,setImmediate]

第二轮

current task：process，async1 end ,promise.then micro task queue：[] macro task queue：[setTimeout,setImmediate]

第三轮

current task：setTimeout,setImmediate micro task queue：[] macro task queue：[]

最终结果：[script start，async1 start，async2，promise1，script end,process,async1 end,promise2,setTimeout,setImmediate] 同样”async1 end”,”promise2”之间的优先级，因平台而异。