I always thought the old Date is kind of elegant... increment anything with an overflow and it all wraps around correctly, like `d.setDate(d.getDate() + 100)` to advance a date 100 days. "March 208th" is interpreted like you'd expect, as are the hours and minutes and such.
Of course, complete lack of non-local non-GMT time zones is a huge downside.
i'm pretty sure all that stuff works w/ Temporal... Temporal is extremely well-designed, in my experience. the js date object, on the other hand, has insane pitfalls, and i say this as someone who thinks not understanding JS ASI is a "skill issue", among other happily-un-"ergonomic" worldviews...
`d.add({ days: 100 })` also wraps like you'd expect. `d.with({ day: 208 })` becomes the last day of the month instead but "March 208th" is kinda nonsense anyway so whatever. You could emulate it with `d.add({ days: 208 - d.day })`
Of course, complete lack of non-local non-GMT time zones is a huge downside.