UUIDv7 in Javascript

uuid7.js

/**
 * Generate a UUIDv7 as a string (see also: https://datatracker.ietf.org/doc/draft-peabody-dispatch-new-uuid-format/)
 *
 * This function was translated to javascript from the python implementation here: https://github.com/oittaa/uuid6-python
 *
 * The UUIDv7 format is designed to encode a Unix timestamp with
 * arbitrary sub-second precision. The key property provided by UUIDv7
 * is that timestamp values generated by one system and parsed by
 * another are guaranteed to have sub-second precision of either the
 * generator or the parser, whichever is less. Additionally, the system
 * parsing the UUIDv7 value does not need to know which precision was
 * used during encoding in order to function correctly.
 *
 * @license MIT
 *
 * @returns {string}
 */
export function uuid7() {
  const version = 7n;
  // get date.now in nanoseconds as bigint
  const nanoseconds = BigInt(Date.now()) * BigInt(1000000);
  const divmod = (dividend, divisor) => {
    return [dividend / divisor, dividend % divisor];
  }
  const [timestamp_ms, timestamp_ns] = divmod(nanoseconds, 1000000n);
  let subsec = timestamp_ns * (2n ** 20n) / 1000000n;
  let subsec_a = subsec >> 8n;
  let subsec_b = subsec & 0xFFn;
  let uuid_int = (timestamp_ms & 0xFFFFFFFFFFFFn) << 80n;
  uuid_int |= subsec_a << 64n;
  uuid_int |= subsec_b << 54n;
  uuid_int |= BigInt(Math.floor(Math.random() * Math.pow(2, 54)));
  // Set the variant to RFC 4122.
  uuid_int &= ~(0xC000n << 48n)
  uuid_int |= 0x8000n << 48n
  // Set the version number.
  uuid_int &= ~(0xF000n << 64n)
  uuid_int |= version << 76n
  // convert uuid_int to a hex string
  let hex = uuid_int.toString(16)
  hex = hex.padStart(32,'0');
  return `${hex.slice(0,8)}-${hex.slice(8,12)}-${hex.slice(12,16)}-${hex.slice(16,20)}-${hex.slice(20)}`;
}