Array of Doubled Pairs LeetCode solution in JavaScript

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var canReorderDoubled = function (arr) {
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  const hashMap = arr.reduce((map, num) => {
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    const count = map.get(num) ?? 0;
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    return map.set(num, count + 1);
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  }, new Map());
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  const nums = [...hashMap.keys()].sort((a, b) => {
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    return a < 0 && b < 0 ? b - a : a - b;
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  });
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  for (const num of nums) {
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    const count = hashMap.get(num);
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    const pairsCount = hashMap.get(num * 2);
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    if (count > pairsCount) return false;
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    if (count > 0 && pairsCount === undefined) return false;
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    hashMap.set(num * 2, pairsCount - count);
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  }
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  return true;
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};