catstodon/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);
}