stylelint-bundle-worker.js
function exponential(str, options, fn) {
  if (typeof options === 'function') {
    fn = options;
    options = null;
  }

  var opts = options || {};
  var esc = '__ESC_EXP__';
  var exp = 0;
  var res;

  var parts = str.split('{,}');
  if (opts.nodupes) {
    return fn(parts.join(''), opts);
  }

  exp = parts.length - 1;
  res = fn(parts.join(esc), opts);
  var len = res.length;
  var arr = [];
  var i = 0;

  while (len--) {
    var ele = res[i++];
    var idx = ele.indexOf(esc);

    if (idx === -1) {
      arr.push(ele);

    } else {
      ele = ele.split('__ESC_EXP__').join('');
      if (!!ele && opts.nodupes !== false) {
        arr.push(ele);

      } else {
        var num = Math.pow(2, exp);
        arr.push.apply(arr, repeat(ele, num));
      }
    }
  }
  return arr;
}
function exponential(str, options, fn) {
  if (typeof options === 'function') {
    fn = options;
    options = null;
  }

  var opts = options || {};
  var esc = '__ESC_EXP__';
  var exp = 0;
  var res;

  var parts = str.split('{,}');
  if (opts.nodupes) {
    return fn(parts.join(''), opts);
  }

  exp = parts.length - 1;
  res = fn(parts.join(esc), opts);
  var len = res.length;
  var arr = [];
  var i = 0;

  while (len--) {
    var ele = res[i++];
    var idx = ele.indexOf(esc);

    if (idx === -1) {
      arr.push(ele);

    } else {
      ele = ele.split('__ESC_EXP__').join('');
      if (!!ele && opts.nodupes !== false) {
        arr.push(ele);

      } else {
        var num = Math.pow(2, exp);
        arr.push.apply(arr, repeat(ele, num));
      }
    }
  }
  return arr;
}
Expand exponential ranges

`a{,}{,}` => ['a', 'a', 'a', 'a']