Since our application deals with lots of time series data and presents it in multiple ways, we have to perform lots of date operations and use multiple date formats. In some cases date conversions and validation can even become a bottleneck.
There is a centralized system to speed up date conversions and other operations in src/helpers/date-cache.ts. It provides UnifiedDay and UnifiedIsoWeek objects which can be managed through globalDateCache. This system is used in most code, although not 100% consistently. You should definitely try to use it in new code.
A UnifiedDay object represents a single day and contains multiple representations of it (e.g. as Dayjs). UnifiedIsoWeek is the equivalent for weeks, which are used quite a lot in CoV-Spectrum. Days and weeks are linked to each other through isoWeek and firstDay fields for fast lookups.
You can get a UnifiedDay or UnifiedIsoWeek by calling globalDateCache.getDay or globalDateCache.getIsoWeek. This is cheap from the second call for the same date, which really helps for our use case.
UnifiedDay objects will be reference equal (===) if they represent the same day. The same holds for UnifiedIsoWeek. This allows using these objects as keys for Map or Set instead of using specially formatted strings. Note that you must use globalDateCache for this to work - do not call new DateCache() yourself, except in tests.