理解 JavaScript Promise 的执行顺序：微任务队列与并发

Promise.resolve()
  .then(() => console.log(1))
  .then(() => console.log(2))
  .then(() => console.log(3));

Promise.resolve()
  .then(() => console.log(11))
  .then(() => console.log(12));

Promise.resolve()
  .then(() => console.log(111))
  .then(() => console.log(122));

const sequence = [1, 2, 3, 11, 12, 111, 122];

const rules = [
  // All Promises
  { type: 'condition', operator: 'lt', left: 1, right: 11 },
  { type: 'condition', operator: 'lt', left: 11, right: 111 },
  // 1st Promise
  { type: 'condition', operator: 'gt', left: 2, right: 1 },
  { type: 'condition', operator: 'gt', left: 3, right: 2 },
  // 2nd Promise
  { type: 'condition', operator: 'gt', left: 12, right: 11 },
  // 3rd Promise
  { type: 'condition', operator: 'gt', left: 122, right: 111 }
];

const main = () => {
  const validPermutations = permutator(sequence)
    .filter(p => validate(p, rules));
  validPermutations.forEach((p, i) => {
    console.log(`Permutation #${i + 1}: ${JSON.stringify(p).replace(/,/g, ', ')}`)
  });
  console.log('Valid permutations:', validPermutations.length);
};

const validate = (sequence, rules) => {
  return rules.every(rule => {
    switch (rule.type) {
      case 'condition':
        const
          indexLeft = sequence.indexOf(rule.left),
          indexRight = sequence.indexOf(rule.right);
        switch (rule.operator) {
          case 'gt':
            return indexLeft > indexRight;
          case 'lt':
            return indexLeft < indexRight;
          default:
            return false;
        }
        break;
      default:
        return false;
    }
  });
};

const permutator = (inputArr) => {
  const result = [];
  permute(inputArr, result);
  return result;
}

const permute = (arr, res, m = []) => {
  if (arr.length === 0) res.push(m);
  else {
    for (let i = 0; i < arr.length; i++) {
      const curr = arr.slice(), next = curr.splice(i, 1);
      permute(curr.slice(), res, m.concat(next));
    }
  }
}

main();