Question

我对Promise的使用有点困惑。请参阅以下示例：

Q1。如何停止连锁电话？

＆＃13;

const wait = (duration = 0) => {
  return new Promise((resolve) => {
    setTimeout(resolve, duration);
  });
};

const asyncTask1 = () => {
  return wait(1000).then(() => {
    console.log('task1 takes 1s.');
  });
};

const asyncTask2 = () => {
  return wait(3000).then(() => {
    console.log('task2 takes 3s.');
  });
};

Promise.resolve()
  .then(() => {
    asyncTask1();
  })
  .then(() => {
    asyncTask2();
  })
  .catch(() => {
    console.log('fail.');
  });

＆＃13;

如代码所示，asyncTask2在asyncTask1完成之前不会运行。但问题是如果asyncTask1失败，我该如何停止链调用。即asyncTask2因为asyncTask1失败而无法运行。注意：asyncTask1中没有生成错误或异常，我想使用状态（成功或失败）来决定asyncTask1的结果。

Q2。当我使用Promise.all（）时，如何知道哪个任务会生成异常？

＆＃13;

const wait = (duration=0) => {
  return new Promise((resolve) => {
    setTimeout(resolve, duration);
  });
};

const asyncTask1 = () => {
  return wait(1000).then(() => {
    console.log('task1 takes 1s.');
  });
};

const asyncTask2 = () => {
  return wait(3000).then(() => {
    console.log('task2 takes 3s.');
  });
};

Promise
  .all([asyncTask2(), asyncTask1()])
  .then(() => {
    console.log('all done.');
  })
  .catch((e) => {
    console.log('error');
  });

＆＃13;

上面的代码可以成功运行，但如果asyncTask1或asyncTask2失败，它将进入catch函数。所以问题是如何知道异常是来自asyncTask1还是asyncTask2？

Answer 1

您可以使用Array.prototype.map()来调用数组中设置的函数，throw index在.map()回调.catch()内发生错误的const wait = (duration=0) => { return new Promise((resolve) => { setTimeout(resolve, duration); }); }; const asyncTask1 = () => { return wait(1000).then(() => { console.log('task1 takes 1s.'); }); }; const asyncTask2 = () => { return wait(3000).then(() => { throw new Error() console.log('task2 takes 3s.'); }); }; let arr = [asyncTask2, asyncTask1]; Promise .all(arr.map((p, index) => p().catch(err => {throw new Error(err + " at index " + index)}))) .then(() => { console.log('all done.'); }) .catch((e) => { console.log('error', e); });

＆＃13;

{{1}}

＆＃13;

当我使用promise.all []或停止链调用

1 个答案: