What Is a UUID?

// 1. Browser Native Web Crypto API (UUID v4)
const uuidV4 = crypto.randomUUID();
console.log("UUID v4:", uuidV4);
// "9b1deb4d-3b7d-4bad-9bdd-2b0d7b3dcb6d"
// Notice: 13th char is '4' (version), 17th char starts with [8,9,a,b] (variant)

// 2. Modern UUID v7 (Time-Ordered for Fast Database Indexing)
// Byte breakdown: [48-bit timestamp ms] + [version 7] + [random bits]
function generateUuidV7() {
  const timestamp = BigInt(Date.now());
  const randomBytes = crypto.getRandomValues(new Uint8Array(10));
  
  // High 48 bits: Unix timestamp in ms
  const timeHex = timestamp.toString(16).padStart(12, '0');
  
  // Format into canonical groups with version 7 and variant 2
  return `${timeHex.slice(0, 8)}-${timeHex.slice(8, 12)}-7${randomBytes[0].toString(16).slice(0,1)}${randomBytes[1].toString(16).padStart(2,'0')}-${((randomBytes[2] & 0x3f) | 0x80).toString(16).padStart(2,'0')}${randomBytes[3].toString(16).padStart(2,'0')}-${Array.from(randomBytes.slice(4)).map(b => b.toString(16).padStart(2,'0')).join('')}`;
}