Convert Instant/ZonedDateTime -> Date

[pauldraper]

Converting to Date currently requires:

new Date(instant.epochMilliseconds)

new Date(zonedDateTime.epochMilliseconds)

This is awkward, and requires remembering the unit for Dates. (seconds? millis? nanos?)

I suggest offering convenience functions:

Date.fromTemporalInstant(instant)
Date.fromTemporalZonedDateTime(zonedDateTime)

For adoption, it's important that converting to/from Dates is easy and rebost.

[ptomato]

Thanks for taking the time to give feedback!

There's more background on this decision in #515 and #751 if you'd like more reading material.

Direct conversion between legacy Date and ZonedDateTime is actually something that we intentionally omitted. The data model of Date does not include a time zone, although many developers incorrectly believe that it does because it has two methods for each unit such as getHour()/getUTCHour() that use the current system time zone and UTC, respectively. We felt that converting between ZonedDateTime and Date was likely to lead to confusion in that regard. Additionally, it would have introduced a new point where system information (the user's time zone setting) was accessed implicitly: something that TC39 would not accept.

Although I can't find it documented anywhere now, if my memory serves, we considered that new Date(instant.epochMilliseconds) was sufficiently convenient for a conversion whose usage would drop off after an initial period of adoption, and didn't need a separate method.

At this stage of the proposal, the scope is nailed down and we aren't going to add new methods. If you'd like, you can open an issue at js-temporal/proposal-temporal-v2 and we can track whether we get a lot of requests for it.

[pauldraper]

Okay, I filed an issue for v2: js-temporal/proposal-temporal-v2#31

Though I'll go on record that I'm skeptical on adoption without having an easy(ier) Temporal <-> Date conversion.