1. 输出是什么

Promise.resolve().then(() => {
  console.log(1);

  Promise.resolve().then(() => {
    console.log(2);
  });

}).then(() => {
  console.log(3);
});

console.log(4);

2. 输出是什么

console.log('x');

setTimeout(() => {
  console.log('y');
  Promise.resolve().then(() => {
    console.log('z');
  });
}, 0);

Promise.resolve().then(() => {
  console.log('p');
});

console.log('q');

3. 输出是什么

console.log(1);

setTimeout(() => {
  console.log(2);

  Promise.resolve().then(() => {
    console.log(3);
  });

}, 0);

Promise.resolve().then(() => {
  console.log(4);

  setTimeout(() => {
    console.log(5);
  }, 0);
});

setTimeout(() => {
  console.log(6);
}, 0);

console.log(7);

4.输出是什么

async function test() {
  console.log(1);

  await Promise.resolve();
  console.log(2);

  setTimeout(() => {
    console.log(3);
  }, 0);

  await 4;
  console.log(5);
}

console.log(6);

test();

Promise.resolve().then(() => {
  console.log(7);
});

setTimeout(() => {
  console.log(8);
}, 0);

console.log(9);

5. 输出是什么

        async function fn() {
            //创建一个promise
            console.log('start');
            let isSuccess = await new Promise((res, rej) => {
                console.log('3');
                // 异步操作
                setTimeout(() => {
                    console.log("定时器完成")
                    res(1)
                }, 0)
            })
            console.log('end');
            // console.log(isSuccess);
        }
        console.log(1);
        fn()
        console.log(2);

这里的执行顺序是 1 start

然后await执行 new Promise

new Promise 的执行器同步执行 → 打印 3

执行器内的 setTimeout 注册一个宏任务（0ms）

async 函数在 await 处 暂停，剩余代码保存起来（不会加入微任务队列，等待 Promise resolve）

也就是说 await会等待后面的promise完成之后再将后续代码放入微任务队列 现在暂时跳出async函数

打印2

然后宏任务队列定时器完成 打印定时器完成

➡ 使 Promise resolved ➡ 触发 await 的恢复逻辑

然后await检测到promise完成 将后续代码放入微任务队列

也就是执行end

6. 输出是什么

//如果await后是new Promise 先执行里面同步代码 然后暂停
//如果是Promise.resolve().then()就把then放到微任务队尾 然后暂停
//如果是Promise.resolve(0) 则直接把await下面的代码包装成微任务放入队尾
async function task1() {
  console.log('A');

  await Promise.resolve().then(() => {
    console.log('B');
  });

  console.log('C');

  await 0;

  console.log('D');
}

async function task2() {
  console.log('E');

  await task1();

  console.log('F');
}

console.log('G');

task2();

Promise.resolve().then(() => {
  console.log('H');
}).then(() => {
  console.log('I');
});

console.log('J');


//g e  a j b h c     i d f

7. 输出是什么

async function alpha() {
    console.log('A');

    await Promise.resolve().then(() => {
        console.log('B');
    });

    console.log('C');

    await 0;

    console.log('D');
}

async function beta() {
    console.log('E');

    await alpha();

    console.log('F');

    await Promise.resolve();

    console.log('G');
}

console.log('H');

beta();

Promise.resolve().then(() => {
    console.log('I');
}).then(() => {
    console.log('J');
});

console.log('K');