练习题

输出打印结果

async function m1() {
  return 1;
}

async function m2() {
  const n = await m1();
  console.log(n);
  return 2;
}

async function m3() {
  const n = m2();
  console.log(n);
  return 3;
}

m3().then((n) => {
  console.log(n);
});

m3();

console.log(4);

查看答案

备注:因为 m2函数没有await关键字 所以m2函数返回就是一个Promise pending

Promise pending,Promise pending,4,1,3,1

输出打印结果

var a;
var b = new Promise((resolve, reject) => {
  console.log("promise1");
  setTimeout(() => {
    resolve();
  }, 1000);
})
  .then(() => {
    console.log("promise2");
  })
  .then(() => {
    console.log("promise3");
  })
  .then(() => {
    console.log("promise4");
  });

a = new Promise((resolve, reject) => {
  console.log(a);
  await b;
  console.log(a)
  console.log('after1')
  await a;
  resolve(true)
  console.log('after2')
});

 console.log('end')

查看答案

备注: 因为第一个Promise的链式调用 所以b的状态就等于最后一个的Promise的状态

promise1,undefined,promise2,promise3,promise4,Promise pending,after1