Получить перестановки строки

function permutations(str) {
  const chars = [...str];
  const res = [];

  function dfs(start) {
    if (start === chars.length) {
      res.push(chars.join(''));
      return;
    }
    const seen = new Set();
    for (let i = start; i < chars.length; i++) {
      if (seen.has(chars[i])) continue; // skip dupes
      seen.add(chars[i]);
      [chars[start], chars[i]] = [chars[i], chars[start]];
      dfs(start + 1);
      [chars[start], chars[i]] = [chars[i], chars[start]];
    }
  }

  dfs(0);
  return res;
}

permutations('abc'); // abc, acb, bac, bca, cab, cba