2

Is the IANA timezone data in nodejs embedded in the Node.js code or does it take the data from the OS?

It seems that it has its own version as process.versions returns the time zone version as stated here. If so do I need to install a new Node.js version to update the timezone data or is there another way?

hippietrail
  • 15,848
  • 18
  • 99
  • 158
ziv
  • 3,641
  • 3
  • 21
  • 26

1 Answers1

5

Node.js gets its timezone data from the ICU library, aka International Components for Unicode, which also provides API artefacts to obtain timezone data. Generally, neither Node.js nor the ICU library query external timezone files from the operating system. The ICU library uses its own set of data files including IANA timezone data which is gathered at build time. Note beyond, the tz property provided by process.versions refers to timezone data portion as part of the ICU library. I'll get back to this later.

Depending the Node.js distribution you use different build options may apply as described in the Node.js docs, section "Internationalization Support":

  • "small-icu": The ICU library is bound statically as well as a subset of the ICU data which is compiled into the executable. Apparently "small-icu" is the common build option used for Node.js distributions provided by Nodejs.org (for Linux, at least). However, it is possible to overlay the builtin data with a ICU data archive loaded from file (see docs, section "Providing Icu Data at Runtime"). Various NPM packages exist to download the archive, such as node-icu and full-icu).

  • "full-icu": Same as "small-icu" but with a full ICU dataset compiled into the executable (which results in a fairly large executable).

  • "system-icu": The ICU library is bound dynamically with the Node.js executable and needs to be installed as a prerequisite to the Node.js installation. As such the library can be updated independently from node.js installation.

  • "none": The ICU library is not bound at all. hence there is no timezone data available.

Generally, it should be noted ICU data archive is updated less frequently than the IANA timezone data. Therefore, you may have to deal with outdated timezone information in Node.js even if you always install the latest Node.js LTS release. This is indicated by the tz properties value 2018e which indicates a fairly old version of timezone data. The current IANA timezone data is dated from March 2019. For most applications this should be fine, but if you need highest accuracy you need to look for other options:

  • Getting a Node.js distribution built with "system-icu" (or most likely build your own) may be a choice, however, I am not sure you can really dynamically bind Node.js with a newer version of the library at runtime. There may be restriction to this.
  • Building your own custom ICU data archive may be another choice, but it appears to be fairly complex if you have never dealt with the ICU library before.
  • Another option is to use Node.js libraries like moment-timezone or TimezoneComplete which included their own compilations of timezone. The latter seems to be interesting as the subordinate tzdata package which contains the timezone dataset is updated frequently. However, a disadvantage of the library approach is, you're forced to use a specific API provided by the library rather than "standard" Javascript/Node.js APIs. This may be problematic in particular if you have a large codebase to maintain an the code bases on library which handle date/time objects.
Marcus
  • 1,097
  • 11
  • 21
  • Is there way to detect if the installed version is an icu build? – ziv Apr 03 '19 at 06:21
  • Check the output of `process.config`. It returns an object which contains variables which should also contain a property `icu_small`. In my case it is set to true. https://nodejs.org/api/process.html#process_process_version – Marcus Apr 03 '19 at 08:06
  • See also https://techoverflow.net/2018/09/19/fixing-nodejs-intl-datetimeformat-not-formatting-properly-for-locales/ – Marcus Apr 03 '19 at 08:45
  • @ziv - I have dome some more in-depth research on the matter and revised my answer accordingly. – Marcus Apr 08 '19 at 20:56