Increasing Decreasing String LeetCode solution in JavaScript

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/**
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 * @param {string} s
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 * @return {string}
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 */
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var sortString = function (s) {
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  const counts = [...s].reduce(
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    (acc, cur) => ((acc[cur.charCodeAt() - 97] += 1), acc),
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    new Array(26).fill(0)
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  );
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  const result = [];
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  const pick = (code) => {
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    if (counts[code]) {
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      result.push(String.fromCharCode(code + 97));
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      counts[code] -= 1;
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    }
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  };
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  while (result.length < s.length) {
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    for (let i = 0; i < counts.length; i++) pick(i);
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    for (let i = 0; i < counts.length; i++) pick(counts.length - 1 - i);
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  }
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  return result.join("");
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};