Check Whether Two Strings are Almost Equivalent LeetCode solution in JavaScript

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var checkAlmostEquivalent = function (word1, word2) {
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  const hm = new Map();
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  const addToHm = (ch, add) => {
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    if (hm.has(ch)) hm.set(ch, hm.get(ch) + (add ? +1 : -1));
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    else hm.set(ch, add ? +1 : -1);
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  };
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  for (let i = 0; i < word1.length; i++) {
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    addToHm(word1[i], true);
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    addToHm(word2[i], false);
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  }
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  for (const val of hm.values()) if (Math.abs(val) > 3) return false;
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  return true;
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};