练习题

求输出结果

console.log(1);
new Promise((resolve, reject) => {
  console.log(2);
  resolve();
}).then((res) => {
  console.log(3);
});
console.log(4);

Details

查看答案

1,2,4,3

setTimeout 和 Promise 的执行顺序

setTimeout(function () {
  console.log(1);
}, 0);

new Promise(function (resolve, reject) {
  console.log(2);
  resolve();
})
  .then(function () {
    console.log(3);
  })
  .then(function () {
    console.log(4);
  });

console.log(6);

Details

查看答案

2,6,3,4,1

setTimeout 和 Promise 的执行顺序

setTimeout(function () {
  console.log(1);
}, 0);

new Promise(function (resolve, reject) {
  console.log(2);
  for (var i = 0; i < 100; i++) {
    if (i === 10) {
      console.log(10);
    }
    i == 99 && resolve();
  }
  console.log(3);
}).then(function () {
  console.log(4);
});
console.log(5);

Details

查看答案

2,10,3,5,4,1

求输出结果

console.log("start");
setTimeout(() => {
  console.log("children2");
  Promise.resolve().then(() => {
    console.log("children3");
  });
}, 0);

new Promise(function (resolve, reject) {
  console.log("children4");
  setTimeout(function () {
    console.log("children5");
    resolve("children6");
  }, 0);
}).then((res) => {
  // flag
  console.log("children7");
  setTimeout(() => {
    console.log(res);
  }, 0);
});

Details

查看答案

start,children4,children2,children3,children5,children7,children6

请写出下面代码的运行结果

async function async1() {
  console.log("async1 start");
  await async2();
  console.log("async1 end");
}
async function async2() {
  console.log("async2");
}
console.log("script start");
setTimeout(function () {
  console.log("setTimeout");
}, 0);
async1();
new Promise((resolve) => {
  console.log("promise1");
  resolve();
}).then(function () {
  console.log("promise2");
});
console.log("script end");

查看答案

script start,async1 start,async2,promise1,script end

async1 end, promise2,setTimeout

将上一道题目变换一下，求输出

async function async1() {
  console.log("async1 start");
  await async2();
  console.log("async1 end");
}
async function async2() {
  new Promise(function (resolve) {
    console.log("promise1");
    resolve();
  }).then(function () {
    console.log("promise2");
  });
}
console.log("script start");
setTimeout(function () {
  console.log("setTimeout");
}, 0);
async1();
new Promise(function (resolve) {
  console.log("promise3");
  resolve();
}).then(function () {
  console.log("promise4");
});
console.log("script end");

查看答案

script start,async1 start,promise1,promise3,script end

promise2,async1 end,promise4,setTimeout

将上面的题目变换一下，求输出

async function async1() {
  console.log("async1 start");
  await async2();
  setTimeout(function () {
    console.log("setTimeout1");
  }, 0);
}
async function async2() {
  setTimeout(function () {
    console.log("setTimeout2");
  }, 0);
}
console.log("script start");
setTimeout(function () {
  console.log("setTimeout3");
}, 0);
async1();
new Promise(function (resolve) {
  console.log("promise1");
  resolve();
}).then(function () {
  console.log("promise2");
});
console.log("script end");

查看答案

script start,async1 start,promise1,script end

promise2,setTimeout3,setTimeout2,setTimeout1

求输出结果

async function async1() {
  console.log("a");
  await async2();
  console.log("b");
}

async function async2() {
  console.log("c");
}

console.log("d");
async1();

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

new Promise((resolve, reject) => {
  console.log("f");
  resolve();
}).then(() => {
  console.log("g");
});

查看答案

d,a,c,f,b,g,e

求输出结果

console.log("1");
async function async1() {
  console.log("2");
  await async2();
  console.log("3");
}
async function async2() {
  console.log("4");
}

Promise.resolve().then(function () {
  console.log("5");
});

setTimeout(function () {
  console.log("6");
  Promise.resolve().then(function () {
    console.log("7");
  });
  new Promise(function (resolve) {
    console.log("8");
    resolve();
  }).then(function () {
    console.log("9");
  });
});

async1();

new Promise(function (resolve) {
  console.log("10");
  resolve();
}).then(function () {
  console.log("11");
});
console.log("12");

查看答案

1,2,4,10,12,5,3,11

6,8,7,9