mastodon/app/javascript/mastodon/uuid.ts

export default function uuid(a?: string): string {
  return a ? ((a as any as number) ^ Math.random() * 16 >> (a as any as number) / 4).toString(16) : ('' + 1e7 + -1e3 + -4e3 + -8e3 + -1e11).replace(/[018]/g, uuid);
}