Groups of Special-Equivalent Strings LeetCode solution in JavaScript

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var numSpecialEquivGroups = function (words) {
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  const set = new Set();
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  const a = "a".charCodeAt(0);
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  const alphaCounter = new Array(26).fill(0);
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  for (const word of words) {
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    const [even, odd] = [[...alphaCounter], [...alphaCounter]];
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    word.split("").forEach((l, i) => {
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      l = l.charCodeAt(0) - a;
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      if (i % 2) odd[l]++;
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      else even[l]++;
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    });
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    const hashkey = even.join("") + odd.join("");
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    set.add(hashkey);
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  }
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  return set.size;
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};