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