How to decode a UUID's version, variant, and timestamp using plain JavaScript

A UUID is a 128-bit identifier written as 32 hex digits, and its version and variant can be determined by reading just two specific character positions in the string. Three UUID versions — v1, v6, and v7 — embed a timestamp, though each uses a different epoch and time unit, making extraction slightly complex. A developer built a dependency-free JavaScript decoder to inspect UUIDs received from external systems that lack documentation. The decoder normalizes various input formats, applies bitmasking in the correct order to identify the variant, and uses BigInt arithmetic only where the timestamp exceeds JavaScript's safe integer range. The post focuses less on the feature itself and more on the verification process used to confirm the decoder's correctness.