UUIDバージョン別リファレンス（RFC 4122 / RFC 9562準拠）

import crypto from 'node:crypto';

// 1. UUID v4 (Native built-in)
const idV4 = crypto.randomUUID();
console.log('UUIDv4:', idV4);

// 2. UUID v7 (Unix millisecond timestamp + randomness)
function generateUUIDv7() {
  const bytes = new Uint8Array(16);
  crypto.getRandomValues(bytes);
  const now = Date.now();

  // Timestamp (48 bits)
  bytes[0] = (now / 0x10000000000) & 0xff;
  bytes[1] = (now / 0x100000000) & 0xff;
  bytes[2] = (now / 0x1000000) & 0xff;
  bytes[3] = (now / 0x10000) & 0xff;
  bytes[4] = (now / 0x100) & 0xff;
  bytes[5] = now & 0xff;

  // Version 7 (0b0111)
  bytes[6] = (bytes[6] & 0x0f) | 0x70;
  // Variant RFC 4122 (0b10)
  bytes[8] = (bytes[8] & 0x3f) | 0x80;

  return [...bytes].map((b, i) => 
    ([4, 6, 8, 10].includes(i) ? '-' : '') + b.toString(16).padStart(2, '0')
  ).join('');
}