Reading the proposal page “ Time Zones and Resolving Ambiguity”[1], it only mentions that it uses the IANA time zone database[2] not when it updates it. However

Reading the proposal page “ Time Zones and Resolving Ambiguity”[1], it only mentions that it uses the IANA time zone database[2] not when it updates it. However I imagine the users computer has access to this database as well and probably handles it being updated. I’m not sure about this. It’s also entirely possible for the browser to download this database and maintain it too, separately from updates. I’m sure it depends on the implementation. [1] https://tc39.es/proposal-temporal/docs/timezone.html https://tc39.es/proposal-temporal/docs/timezone.html [2] https://en.wikipedia.org/wiki/Tz_database https://en.wikipedia.org/wiki/Tz_database