不断从新的 Promise 获得未定义的结果

Question

const randomIntegerFromInterval = (min, max) => {
  return Math.floor(Math.random() * (max - min + 1) + min);
};

const makeTransaction = (transaction) =>
  new Promise((res, rej) => {
    const delay = randomIntegerFromInterval(200, 500);
    setTimeout(() => {
      const canProcess = Math.random() > 0.3;
      if (canProcess) {
        res(transaction.id, randomIntegerFromInterval(200, 500));
      } else {
        rej(transaction.id);
      }
    }, delay);
  });

const logSuccess = (id, time) => {
  console.log(`Transaction ${id} processed in ${time}ms`);
};

const logError = (id) => {
  console.warn(`Error processing transaction ${id}. Please try again later.`);
};

makeTransaction({ id: 70, amount: 150 }).then(logSuccess).catch(logError);

makeTransaction({ id: 71, amount: 230 }).then(logSuccess).catch(logError);

makeTransaction({ id: 72, amount: 75 }).then(logSuccess).catch(logError);

makeTransaction({ id: 73, amount: 100 }).then(logSuccess).catch(logError);

由于某种原因，我不断得到一个未定义的值。还没弄清楚为什么会这样。

输出必须是这样的。请解释是什么问题，或者我应该改变什么。

task_3.js:23 Error processing transaction 73. Please try again later.
task_3.js:19 Transaction 70 processed in 458ms
task_3.js:19 Transaction 72 processed in 354ms
task_3.js:23 Error processing transaction 71. Please try again later.

Answer 1

像这样解决承诺

res({
  id: transaction.id, 
  time: randomIntegerFromInterval(200, 500)
});

然后像这样记录

const logSuccess = ({id, time}) => {
  console.log(`Transaction ${id} processed in ${time}ms`);
};

Answer 2

这是因为执行器函数回调res 和rej 只接受一个参数。你需要把它改成这样：

const randomIntegerFromInterval = (min, max) => {
  return Math.floor(Math.random() * (max - min + 1) + min);
};

const makeTransaction = (transaction) =>
  new Promise((res, rej) => {
    const delay = randomIntegerFromInterval(200, 500);
    setTimeout(() => {
      const canProcess = Math.random() > 0.3;
      if (canProcess) {
        res({id: transaction.id, time: randomIntegerFromInterval(200, 500)});
      } else {
        rej(transaction.id);
      }
    }, delay);
  });

const logSuccess = ({id, time}) => {
  console.log(`Transaction ${id} processed in ${time}ms`);
};

const logError = (id) => {
  console.warn(`Error processing transaction ${id}. Please try again later.`);
};

makeTransaction({ id: 70, amount: 150 }).then(logSuccess).catch(logError);

makeTransaction({ id: 71, amount: 230 }).then(logSuccess).catch(logError);

makeTransaction({ id: 72, amount: 75 }).then(logSuccess).catch(logError);

makeTransaction({ id: 73, amount: 100 }).then(logSuccess).catch(logError);

有关参考，请参阅this：

这两个函数的签名很简单，它们接受任何类型的单个参数。