code: function iterateOverDateUnits(fn, startIndex, endIndex) {
    endIndex = endIndex || 0;
    if (isUndefined(startIndex)) {
      startIndex = YEAR_INDEX;
    }
    for (var index = startIndex; index >= endIndex; index--) {
      if (fn(DateUnits[index], index) === false) {
        break;
      }
    }
  }
docs: Iteration helpers Years -> Milliseconds