Running a simple new Date().toString(). On Node 11, You get something like
'Fri May 10 2019 10:44:44 GMT-0700 (Pacific Daylight Time)'
While on Node 8 you get
'Fri May 10 2019 10:44:44 GMT-0700 (PDT)'
Note the different in timezone abbreviation. Why is that? And how can you force toString() to always return the zone in the abbreviation?
Stolen answer from #ssube who was too lazy to log in and post.
the whole Intl object and default formats were introduced between those two versions, which may have become the new default for Date as well.
After some digging on my own, and reading some of the Intl spec:
The ECMAScript 2015 Internationalization API Specification identifies time zones using the Zone and Link names of the IANA Time Zone Database. Their canonical form is the corresponding Zone name in the casing used in the IANA Time Zone Database.
As to how to revert back to an abbreviated timezone, I am seeing that there are several github repos that suggest using regex, others using an abbreviation Map, or even Ben Nadel who uses some regex to process the short timezone or long timezone, as seen in his blog here
Looks like JavaScript leaves this up to the implementer. Based on the below GitHub Issue for ECMA262, there are known differences between the ways UNIX & Windows handle the timezone value.
Across multiple JS implementations, it seems that Date.prototype.toString writes the timezone (in parens) in a long, locale-dependent form on Windows, but in a short form (2-4 letters) from the tz database on Unix-based OSes. More details in the V8 bug tracker.
The spec is really light on details for Date.prototype.toString:
Return an implementation-dependent String value that represents tv as a date and time in the current time zone using a convenient, human-readable form.
Does anyone have a good memory of why this is the definition? Looks like it goes all the way back to ES1.
Fortunately, it seems that, at this point, implementations have converged on something that's almost always the same, with the exception of the timezone string.
For the timezone string, would it be a good idea to pick one of the two alternatives and standardize it across all platforms? Does anyone have evidence one way or the other whether either of the two is likely to be more web-compatible, or whether we need to preserve the variation?
Additionally, it looks like there is still active discussion in the V8 Issues for Date.prototype.toString() normalization.
Going through the NodeJS there doesn't seem to be an explicit mention of this in their change logs for v10+.
Update
After digging through V8 commits, it looks like there is a new Timezone Names Cache implemented for performance in V8 when using Date.prototype.toString(). Based on the below excerpt from the message for this commit, it seems like this change is why there is a difference between Node v8 & Node v11
To speed up Date.prototype.toString(), this patch adds a cache in the
DateCache for the string short name representing the time zone.
Because time zones in a particular location just have two short names
(for DST and standard time), and the DateCache already understands
whether a time is in DST or not, it is possible to keep the result of
OS::LocalTimezone around and select between the two based on whether
the time is DST or not.
In local microbenchmarks (calling Date.prototype.toString() in a
loop), I observed a 6-10% speedup with this patch. In the browser, the
speedup may be even greater as the system call needs to do some extra
work to break out of the sandbox. I don't think the microbenchmark is
extremely unrealistic; in any real program which calls
Date.prototype.toString() multiple times, the cache should hit almost
all of the time, as time zone changes are rare.
The proximate motivation for this patch was to enable ICU as a backend
for timezone information, which is drafted at
https://codereview.chromium.org/2724373002/ The ICU implementation of
OS::LocalTimezone is even slower than the system call one, but this
patch makes their performance indistinguishable on the microbenchmark.
In the tz database, many timezones actually do have a number of
different historical names. For example, America/Anchorage went
through a number of changes, from AST to AHST to YST to AKST. However,
both ICU and the Linux OS interfaces just report the modern timezone
name in tests for the appropriate timezone name, even for historical
times. I can see why this would be:
- For ICU, CLDR only has two short names in the data file: the one for dst and non-dst
- For Linux, the timezone names do seem to make it into the /etc/localtime file. However, glibc assumes there are only two
relevant names and selects between them, as you can see in its
implementation of localtime_r:
http://bazaar.launchpad.net/~vcs-imports/glibc/master/view/head:/time/tzset.c#L573
So, this cache should be valid until we switch to a more accurate
source of short timezone names.
Related
Getting different output for both browser if we select '(UTC +01:00) Brussels, Copenhagen, Madrid, Paris' in system.
var tz = jstz.determine();
var tzName = tz.name();
Output:
IE11: Europe/Berlin
Chrome: Europe/Paris
From the jsTimeZoneDetect docs:
Limitations
This script does not do geo-location, nor does it care very much about historical time zones. So if you are unhappy with the time zone "Europe/Berlin" when the user is in fact in "Europe/Stockholm" - this script is not for you. They are both identical in modern time.
Indeed, if we carefully examine and compare the history of time zone changes for Berlin and Paris, we find that they have been identical since 1980. Thus, unless your application is dealing with dates before 1980, it is inconsequential whether you detect Europe/Berlin or Europe/Paris.
As to which is more correct, the CLDR windowsZones.xml file (which is the canonical mapping between Windows and IANA time zones) contains the following:
<!-- (UTC+01:00) Brussels, Copenhagen, Madrid, Paris -->
<mapZone other="Romance Standard Time" territory="001" type="Europe/Paris"/>
Chrome uses the Intl API, which internally uses ICU, which contains the CLDR data. Thus, Chrome is providing the more correct answer. You should get the same answer in FireFox, Edge, and other modern web browsers.
Internet Explorer is older and doesn't contain the data needed to resolve this correctly. Thus, libraries like jsTimeZoneDetect (and also moment-timezone via moment.tz.guess()) first try to use the Intl approach, but when not available they make an educated guess by testing various known points in time for their UTC offset changes. Since it's just a guess, it's sometimes going to be imprecise.
If you are interested, there's a community-maintained compatibility chart that tracks which browsers support the "correct" time zone detection process. Expand the "DateTimeFormat" section and check the row labeled "resolvedOptions().timeZone defaults to the host environment"
I read in the MDN documentation that:
toLocaleTimeString() without arguments depends on the
implementation,the default locale, and the default time zone
What does this mean exactly?
And I tried the following code in both Chrome(Version 87.0.4280.88) and Safari browser(Version 14.0).
new Date().toLocaleTimeString()
in Chrome it gives output as
16:57:37
whereas in Safari it gives output as
4:57:37 PM
With regards to the above example can someone explain how the implementation is changing from one browser to another, and why is it so?
Edit:
All this was done using MAC, I tried changing preferred language under Setting -> "Language and Region" to English(US) it was English(India) before, as soon as I did that change and restarted chrome the result became.
4:57:37 PM
But for Safari without doing this change it was able to show in 12 hour format, what was the reason for that?
The specification for toLocaleTimeString states:
This function returns a String value. The contents of the String are implementation-defined, but are intended to represent the “time” portion of the Date in the current time zone in a convenient, human-readable form that corresponds to the conventions of the host environment's current locale.
with the definition of implementation-defined being:
An implementation-defined facility is one that defers its definition
to an external source without further qualification. This
specification does not make any recommendations for particular
behaviours, and conforming implementations are free to choose any
behaviour within the constraints put forth by this specification.
Therefore browsers are free to implement this feature as they see fit.
According to specifications, Node JS (ES5) should use current dts rules when working with Date objects. Current means "for now", not for a particular date. That's not perfect, but enough for me at this moment.
Currently that rules are wrong (due to law changes in Chile).
Simple probe:
console.log(new Date())
Mon Apr 08 2019 12:48:08 GMT-0300 (Chile Summer Time) {}
shows "(Chile Summer Time)" at the end of the default toString for a date. Actually we are not in Summer Time (it ended two days ago) and current offset should be -4 and not -3.
I tried upgrading Node to lates stable release and didn't work. I Don't want to change a lot of code (in production) to use moment.js or equivalent.
Is there any way to update DST rules in an existing Node JS installation?
Thanks in advance
-- Edit --
TZ environment variable is empty.
Tested on Mac OSX (Mojave 10.14.4) and Red Hat (4.8.5-36)
moment.js recognizes zone correctly ("America/Santiago" whith moment.tz.guess())
The change for Chile you mentioned was part of IANA TZ data version 2018f, released in October 2018.
Node exposes the tz version via process.versions.tz. The current shipping 10.15.3 LTS version returns 2018e, which explains why you aren't seeing the update. I assume this will be updated at some future date.
Node gets its IANA data via ICU. There are instructions for different ways to compile Node's ICU support (system-icu, small-icu, full-icu) documented here, which apply if you are building Node yourself from source code. Alas, I cannot find any mechanism for updating Node's ICU data directly, without building Node yourself.
ICU has documentation on how to update time zone data without updating all of ICU. however, I cannot see anywhere that Node is taking advantage of this capability.
Thus, when it comes to updating Node's time zone data - Either it cannot currently be done, or it is poorly documented. Sorry, I don't have a better answer for you than that.
You did say you were using moment-timezone already, which ships its time zone data independently. If you use only moment functions (rather than the Date object), then you should get the correct result.
I am using JavaScript Intl API to detect the user's timezone in the browser:
Intl.DateTimeFormat().resolvedOptions().timeZone
While this API looks stable, I don't know what to do with the next. On my Windows 10 machine, the timezone is set to US Eastern Standard Time:
C:\> tzutil /g
US Eastern Standard Time
In Firefox and Edge the above JavaScript code results with "America/Indiana/Indianapolis", while Chrome returns just "America/Indianapolis".
Why this yields different results in different browsers? Is it a Chrome bug or should I transform the time zones somehow before processing them on the server?
On Ubuntu (which is my server's OS), if I list available time zones with timedatectl list-timezones, there is "America/Indiana/Indianapolis", but there is no "America/Indianapolis". Because of this issue I cannot accept Chrome's "America/Indianapolis" from the client, as I grab the "available time zones list" from the output of timedatectl list-timezones. Which behavior should I apply here?
Any help is appreciated. Thank you!
Chrome, like many others, gets its time zone information through ICU, which in turn sources from CLDR, which in part sources from IANA.
There is a subtle difference between IANA and CLDR with regard to canonicalization.
IANA treats the preferred form of the time zone identifier as canonical. If the preferred form changes, they make the new one primary (a Zone entry) and move the old one to an alias (a Link entry).
CLDR treates the first form of the time zone identifier as canonical. That is, the first time it appeared in CLDR, it is locked in forever. If a new form ever appears, it is added as an alias in the /common/bcp47/timezone.xml file.
Taking your case of Indianapolis:
IANA Zone entry (reference here)
Zone America/Indiana/Indianapolis ...
IANA Link entry (reference here)
Link America/Indiana/Indianapolis America/Indianapolis
In CLDR, the primary zone is listed first in the "aliases" attribute, followed by other aliases. (reference here)
<type name="usind" description="Indianapolis, United States" alias="America/Indianapolis America/Fort_Wayne America/Indiana/Indianapolis US/East-Indiana"/>
The same thing can be found with Asia/Calcutta vs. Asia/Kolkata and several other examples.
Additionally, be aware that the Windows time zone mappings also source from CLDR, in the /common/supplemental/windowsZones.xml file. You'll notice there that US Eastern Standard Time is mapped to America/Indianapolis. So the difference between browsers depends very much on which canonicalization rules are followed.
In the end, it doesn't really matter which alias is used. They point at the same data.
Also worth pointing out, that particular Windows zone should only be selected if you care about historical time changes in Indiana. If you are just in the US Eastern time zone, you should set your system to "Eastern Standard Time", rather than "US Eastern Standard Time". (Yes, those IDs are confusing...)
zone.tab is incomplete. Some time zones are represented as symbolic links:
$ find /usr/share/zoneinfo/America -name Indianapolis -exec file {} \;
/usr/share/zoneinfo/America/Indiana/Indianapolis: symbolic link to ../Indianapolis
/usr/share/zoneinfo/America/Indianapolis: timezone data, version 2, 7 gmt time flags, 7 std time flags, no leap seconds, 99 transition times, 7 abbreviation chars
I'm not sure how/why each browser returns a different result (probably they read from different sources and/or it can be due to how each implements Intl.DateTimeFormat). But it doesn't matter, because both are the same timezone.
If you check this list, you'll see that America/Indianapolis links to America/Indiana/Indianapolis. Those names in the format Region/City are maintained by IANA and it's probably one of the best sources we have about timezone information.
IANA also keeps a backward file that maps those 2 names, with America/Indiana/Indianapolis being the most recent one.
So one alternative is to get a copy of the backward file and use it to map whatever name you receive to the respective new name, and also validate against your server's timezone list.
I have set a deadline in UTC, as shown below, and I'm wondering what exactly the toLocaleString() method will do to it on user's local machines. For instance, will it account for daylight savings if they are in a timezone that recognizes it? Or will I need to insert additional code that checks where the user is, and then fixes the displayed time?
http://javascript.about.com/library/bldst.htm
var deadline = new Date('5/1/2013 ' + "16:15" + ' UTC');
alert(deadline.toLocaleString());
In general, the answer is yes. JavaScript will represent the UTC value at the appropriate local time based on the time zone settings of the computer it is running on. This includes adjustment for DST. However, as others have pointed out, the details are implementation specific.
If you want a consistent output, I would use a library to format your dates instead of relying on the default implementation. The best library (IMHO) for this is moment.js. The live examples on their main page will give you an idea of what it can do.
UPDATE
If you are passing UTC values that you want converted to the correct local time, and that time falls into a period where the time zone rules are different than the current one - then the results will be invalid. This is crazy, but true - and by design in the ECMA spec. Read - JavaScript Time Zone is wrong for past Daylight Saving Time transition rules
We don't know what exactly the toLocaleString method does (§15.9.5.5):
This function returns a String value. The contents of the String are
implementation-dependent, but are intended to represent the Date in
the current time zone in a convenient, human-readable form that
corresponds to the conventions of the host environment’s current
locale.
But yes, most implementations will consider DST if it is active in the current local timezone. For your example I'm getting "Mittwoch, 1. Mai 2013 18:15:00" - CEST.
Will I need to insert additional code that checks where the user is, and then fixes the displayed time?
I think you can trust toLocaleString - the browser should respect the user's settings. If you want to do it manually, check out timezone.js.
As you use "UTC" the date itself will be UTC format, but the toLocaleString() takes client's locale into account, which means it'll return the date in string updated with all and every changes typical to client's regional and locale settings (DST, date/time format, etc).As JS documentation describes this: "The toLocaleString() method converts a Date object to a string, using locale settings.".If you want to avoid this, use the toUTCString() method instead.I'd also recommend reading the accepted solution for the question Javascript dates: what is the best way to deal with Daylight Savings Time? to avoid (at least, to try to avoid :) future issues related to JS, browsers and locales.Hope this helps!