At first glance, this seems to be in the JodaTime/NodaTime/Js-Joda tradition of representing different "granularities" of date and time information with distinc

At first glance, this seems to be in the JodaTime/NodaTime/Js-Joda tradition of representing different "granularities" of date and time information with distinct types, e.g. with and without timezone information. I'm not sure if there's a formal relationship, since this seems to use different names. I personally like that approach, but I'm not sure how much sense that makes without static typing. (Maybe TypeScript is established enough that JavaScript APIs are now designed with TypeScript in mind?) From experience with js-joda, there's a definitely learning curve compared to moment's "one size fits all" type for all things date related. But I found that a lot of stupid mistakes of the kind "a person's age is wrong for an hour after midnight during daylight savings time" are prevented by default.