Count Vowel Substrings of a String LeetCode solution in JavaScript

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/**
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 * @param {string} word
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 * @return {number}
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 */
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var isVowel = function (c) {
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  return c === "a" || c === "e" || c === "i" || c === "o" || c === "u";
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};
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var countVowelSubstrings = function (word) {
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  let vowelMap = new Map();
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  let total = 0;
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  let totalLen = word.length - 1;
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  for (let i = 0; i <= totalLen; i++) {
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    vowelMap.clear();
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    for (let j = i; j <= totalLen && isVowel(word[j]); j++) {
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      vowelMap.set(word[j], (vowelMap.get(word[j]) ?? 0) + 1);
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      if (vowelMap.size == 5) total++;
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    }
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  }
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  return total;
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};