OS Grid Conversion in Jersey and Channel Islands

[NickSutton]

Pretty simple, the OsGridRef.parse(ref) command does not return an OS Grid reference when utilised in the Channel Islands, despite them having an OS Grid reference: https://bwars.com/content/channel-islands-how-give-location-reference

[chrisveness]

That page confirms "the islands themselves are not covered by the UK national grid", and "all Channel Island grid refs are UTM references" (strictly, MGRS references for UTM coordinates).

utm.js (https://github.com/chrisveness/geodesy/blob/master/utm.js) provides parsing of UTM references and conversions between UTM and lat/long – see also https://www.movable-type.co.uk/scripts/latlong-utm-mgrs.html.