function isEqual(a, b) {
  return (
    a.Subtype === b.Subtype &&
    a.Params.CheckSum.toString() === b.Params.CheckSum.toString() &&
    a.Params.Size === b.Params.Size &&
    a.Params.CreationDate.getTime() === b.Params.CreationDate.getTime() &&
    ((a.Params.ModDate === undefined && b.Params.ModDate === undefined) ||
      a.Params.ModDate.getTime() === b.Params.ModDate.getTime())
  );
}
check two embedded file metadata objects for equality