UUID Generator — TypeScript source

// RFC 4122 v4 UUID, crypto-grade. Falls back to getRandomValues if
// crypto.randomUUID is absent. Pure (no DOM) - the unit-test surface for the
// UUID Generator tool.

export function uuidv4(): string {
  const c = typeof crypto !== 'undefined' ? crypto : undefined;
  if (c && typeof c.randomUUID === 'function') return c.randomUUID();
  const b = new Uint8Array(16);
  (c ?? (globalThis as unknown as { msCrypto: Crypto }).msCrypto).getRandomValues(b);
  b[6] = (b[6] & 0x0f) | 0x40;
  b[8] = (b[8] & 0x3f) | 0x80;
  const h = [...b].map((x) => x.toString(16).padStart(2, '0'));
  return `${h.slice(0, 4).join('')}-${h.slice(4, 6).join('')}-${h.slice(6, 8).join('')}-${h.slice(8, 10).join('')}-${h.slice(10, 16).join('')}`;
}