Find Common Characters LeetCode solution in JavaScript

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var commonChars = function (words) {
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  //record the first word characters  in an array called minFreq
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  //iterater over the rest of the input array
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  //record the characters for each word called freq
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  //update the corresponding minFreq element to the smaller one between each word and the first word
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  //after collect all the words' freq and update the minFreq, iterate over the minReq
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  //push the element to the result
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  let res = [],
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    minFreq = new Array(26).fill(0);
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  let firstWord = words[0];
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  for (let i = 0; i < firstWord.length; i++) {
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    let index = firstWord.charCodeAt(i) - 97;
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    minFreq[index]++;
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  }
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  for (let word of words) {
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    let freq = new Array(26).fill(0);
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    for (let i = 0; i < word.length; i++) {
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      let index = word.charCodeAt(i) - 97;
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      freq[index]++;
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    }
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    for (let i = 0; i < 26; i++) {
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      minFreq[i] = Math.min(minFreq[i], freq[i]);
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    }
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  }
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  for (let i = 0; i < 26; i++) {
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    for (let q = 0; q < minFreq[i]; q++) {
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      let letter = String.fromCharCode(i + 97);
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      res.push(letter);
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    }
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  }
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  return res;
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};