Count Good Meals LeetCode solution in JavaScript

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var countPairs = function (deliciousness) {
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  const n = deliciousness.length;
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  const MOD = 1e9 + 7;
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  const map = new Map();
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  for (const num of deliciousness) {
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    if (!map.has(num)) map.set(num, 0);
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    map.set(num, map.get(num) + 1);
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  }
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  let max = 2 ** 21;
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  let res = 0;
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  for (const [num, count] of map) {
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    let two = 1;
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    while (two <= max) {
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      const diff = two - num;
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      if (diff >= 0 && map.has(diff)) {
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        const otherCount = map.get(diff);
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        if (num != diff) res += count * otherCount;
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        else res += (count * (count - 1)) / 2;
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      }
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      two <<= 1;
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    }
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    map.delete(num);
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  }
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  return res % MOD;
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};