export default function maxIndex(values, valueof) {
  let max;
  let maxIndex = -1;
  let index = -1;
  if (valueof === undefined) {
    for (const value of values) {
      ++index;
      if (value != null
          && (max < value || (max === undefined && value >= value))) {
        max = value, maxIndex = index;
      }
    }
  } else {
    for (let value of values) {
      if ((value = valueof(value, ++index, values)) != null
          && (max < value || (max === undefined && value >= value))) {
        max = value, maxIndex = index;
      }
    }
  }
  return maxIndex;
}