[LegionMammal978]

I do find it annoying how the Temporal API, just like nearly all other datetime APIs, has 0 support for querying leap-second information in any shape or form. Suggested workarounds like temporal-tai all require plugging in a leap-second file and keeping it updated, which is especially painful for client-side JS, where you can't just download a leap-second file from someone else's site thanks to the SOP. Meanwhile, browsers update on a cadence more than sufficient to keep an up-to-date copy, but the datetime APIs refuse to expose leap-second info because they're too committed to "only UTC is in-scope for this project".

(The context is that I want to write some JS tools for astronomical calculations, but UTC conversions need leap-second info, so this trend makes it impossible to write something that Just Works™.)

[schiffern]

  >only UTC is in-scope for this project

  >tools for astronomical calculations

Pity, since UTC is objectively the wrong time for astronomical calculations. Among other problems, UTC runs slightly slower or faster depending on how far the Earth is from the Sun. UTC does not run uniformly (outside of Earth-at-sealevel), instead the length of 1 second will slightly grow or shrink depending on the current configuration of the Solar system.

As you allude to, the correct time scale for this purpose would be TBD (aka Barycentric Dynamical Time), which applies relativistic corrections to act like the atomic clock is fixed at the barycentre of the Solar system. This is the only clock that actually runs "smoothly" for the purposes of astronomical calculations.

https://stjarnhimlen.se/comp/time.html

https://www2.mps.mpg.de/homes/fraenz/systems/systems2art/nod...

[zokier]

> Among other problems, UTC runs slightly slower or faster depending on how far the Earth is from the Sun. UTC does not run uniformly (apart from Earth-at-sealevel), instead the length of 1 second will slightly grow or shrink depending on the current configuration of the Solar system.

That is completely wrong. UTC seconds are exactly SI seconds, which are all the same uniform length (defined by quorum of atomic clocks).

[nightpool]

> where you can't just download a leap-second file from someone else's site thanks to the SOP

WDYM by this? Why does the SOP prevent a website from hosting a leap seconds file? All they need to do is set Access-Control-Allow-Origin to allow websites to access it. Or provide it as a JS file—in which case no headers are necessary at all. All the SOP prevents is you hotlinking someone else's leap-seconds file and using their bandwidth without their opt-in.

> Meanwhile, browsers update on a cadence more than sufficient to keep an up-to-date copy

Is this true? I don't know any browser right now that ships with a copy of a leapseconds data file. Adding such a data file and keeping it up to date would probably be a pretty non-trivial task for new browser developers—just for something the browser will never end up using itself. It's not like the ICU/CLDR files where browsers are going to need them anyway for rendering their own user-interface components.

[LegionMammal978]

> All they need to do is set Access-Control-Allow-Origin to allow websites to access it. All the SOP prevents is you hotlinking someone else's leap-seconds file and using their bandwidth without their opt-in.

They can, but the major providers (read: the ones I would trust to update it) don't. The IERS doesn't [0], the USNO doesn't [1], IANA doesn't [2], and NIST uses FTP [3]. Keep in mind that these files are constantly being downloaded by various clients for NTP and whatnot, it's not like these providers want to restrict public access, they just don't bother to set the header that would allow JS requests.

> Is this true? I don't know any browser right now that ships with a copy of a leapseconds data file.

From ECMA-262:

> It is required for time zone aware implementations (and recommended for all others) to use the time zone information of the IANA Time Zone Database https://www.iana.org/time-zones/.

Any browser that ships with a copy of tzdb, or knows where to find a copy from the OS, should have access to its leapseconds file. Unless you mean that all of them go solely through ICU and its data files? Which I suppose could be an obstacle unless ICU were to start exposing them.

[0] https://hpiers.obspm.fr/iers/bul/bulc/ntp/leap-seconds.list

[1] https://maia.usno.navy.mil/ser7/tai-utc.dat

[2] https://data.iana.org/time-zones/tzdb/leap-seconds.list

[3] ftp://ftp.boulder.nist.gov/pub/time/leap-seconds.list

[burntsushi]

> but the datetime APIs refuse to expose leap-second info because they're too committed to "only UTC is in-scope for this project".

This doesn't make sense on at least two different levels.

First, pedantically, the definition of UTC as a time scale is that it includes leap seconds. So if you're committed to UTC, then you're supporting leap seconds.

Second, and to more broadly address your point, you should say, "they're too committed to 'only the POSIX time scale is in-scope for this project.'" That more accurately captures the status quo and also intimates the problem: aside from specialty applications, basically everything is built on POSIX time, which specifically ignores the existence of leap seconds.

[LegionMammal978]

Sure, but my gripe isn't even that we ought to change the "POSIX time by default" status quo (the ship has long sailed that everyone counts durations by 'calendar seconds'), it's that the underlying libraries don't even provide enough information for "specialty applications" to reliably correct for it, short of perpetually updating it themselves.

[paulddraper]

> I do find it annoying how the Temporal API, just like nearly all other datetime APIs, has 0 support for querying leap-second information in any shape or form.

That’s because human time keeping doesn’t use leap seconds.

[mr_toad]

Can’t you just mirror the data? You could even embed it in the javascript file itself.

[hgs3]

> like nearly all other datetime APIs, has 0 support for querying leap-second information

That's probably because you only need leap second accuracy in niche use cases, like astronomy or GPS. In JavaScript specifically, that kind of accuracy isn't needed for 99% of client-side use cases. Most date-time libraries work with POSIX time which assumes 86,400 seconds each day.

[GoblinSlayer]

Just put it in an npm package.