zeroPad = (n, size) => {
  const nStr = `${n}`;
  const fillLen = size - nStr.length;
  if (fillLen === 0) return nStr;
  assert(fillLen > 0 && fillLen < zeroes.length);
  return `${zeroes[fillLen]}${nStr}`;
}
@param {unknown} n
@param {number} size
@returns {string}