timezones-ical-library
Version:
Easy direct access to the most recent official timezone information for iCalendar files via JavaScript/TypeScript
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[](https://www.npmjs.com/package/timezones-ical-library)
[](https://github.com/add2cal/timezones-ical-library/blob/main/LICENSE)
<br />
# Add to Calendar Time Zones iCal Library
Convert the [IANA (formerly Olson) time zone database files](http://www.iana.org/time-zones) into VTIMEZONE blocks, compatible with the iCalendar specification (RFC2445).
It is based on [vzic](https://github.com/libical/libical/tree/master/vzic), but only provides the VTIMEZONE part to easily put this into any other iCal generator (like the [add-to-calendar-button](https://github.com/add2cal/add-to-calendar-button)).
It is built to be used standalone, via API, or as JavaScript/TypeScript module, hosted as npm package.
<br /><br />
---
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## 📦 Installation / Setup
### 0. Update it
<details>
<summary>Learn more (not required)</summary>
**This step is only relevant if you want to build the package and data on your own and from source!**
_(Requires Node.js as well as Linux as operating system. You would also need to load/include it manually into your codebase.)_
Run ...
```
sudo sh scripts/update-tzdata.sh tzVersionNumber rebuildVzic
```
- with _tzVersionNumber_ being the version of the [IANA time zone database](https://www.iana.org/time-zones) you want to use (e.g. `sudo sh scripts/update-tzdata.sh 2026b`);
- and _rebuildVzic_ as an optional param to rebuild the vzic library from scratch (e.g. `sudo sh scripts/update-tzdata.sh 2026b true`).
</details>
<br />
### 1. Install it
```
npm install timezones-ical-library
```
<br />
### 2. Import it
For CommonJS:
```
require tzLib = require('timezones-ical-library');
```
With ES:
```
import { tzlib_get_ical_block, tzlib_get_offset, tzlib_get_timezones } from 'timezones-ical-library';
```
<br />
### 3. Use it
#### A. Get time zones
Use `tzlib_get_timezones()` to retrieve a list of all available time zone strings.
You can pass `true` to retrieve a JSON formatted string instead of an array.
For CommonJS, you would use `tzLib.tzlib_get_timezones()`.
#### B. Get the iCal time zone block
Use the `tzlib_get_ical_block(tzName)` function to return the proper iCal VTIMEZONE block for a given time zone string (tzName).
Again, pass `true` to retrieve a JSON formatted string instead of an array _(not recommended)_.
For CommonJS, you would use `tzLib.tzlib_get_ical_block(tzName)`.
You will receive an array, holding the VTIMEZONE block first, and the TZID line (additionally) second. The latter one is needed for any further time statement.
Include this into your iCal data to come up with a complete ics file.
A final constellation could look like this:
```diff
BEGIN:VCALENDAR
VERSION:2.0
PRODID:-// github.com/add2cal/add-to-calendar-button //EN
CALSCALE:GREGORIAN
+ BEGIN:VTIMEZONE
+ TZID:America/New_York
+ LAST-MODIFIED:20220824T133813Z
+ X-LIC-LOCATION:America/New_York
+ BEGIN:DAYLIGHT
+ TZNAME:EDT
+ TZOFFSETFROM:-0500
+ TZOFFSETTO:-0400
+ DTSTART:19700308T020000
+ RRULE:FREQ=YEARLY;BYMONTH=3;BYDAY=2SU
+ END:DAYLIGHT
+ BEGIN:STANDARD
+ ZNAME:EST
+ TZOFFSETFROM:-0400
+ TZOFFSETTO:-0500
+ DTSTART:19701101T020000
+ RRULE:FREQ=YEARLY;BYMONTH=11;BYDAY=1SU
+ END:STANDARD
+ END:VTIMEZONE
BEGIN:VEVENT
UID:2022-08-30T19:29:38.618Z@add-to-calendar-button
DTSTAMP:20230214T091500Z
DTSTART;TZID=America/New_York:20230214T091500
DTEND;TZID=America/New_York:20230218T223000
SUMMARY:A sample event
DESCRIPTION:Just some descriptive text...
LOCATION:World Wide Web
STATUS:CONFIRMED
LAST-MODIFIED:20220830T192938Z
SEQUENCE:0
END:VEVENT
END:VCALENDAR
```
#### C. Get a specific offset
Use `tzlib_get_offset(tzName, isoDate, isoTime)` to get specific offset (relative to UTC), based on a provided date and time.
For example, you can provide _tzName_ `'Europe/Berlin'`, _isoDate_ `'2023-05-23'`, and _isoTime_ `'15:45'` in order to retrieve the offset, which applies for this time zone at the 23rd of May in 2023 at exactly 15:45.
<br /><br />
---
<br />
## ⚙️ API
Instead of using this code or the npm package, you could also make use of the free and open API.
### GET a list of all zone names
```
https://tz.add-to-calendar-technology.com/api/zones.json
```
### GET the ics part of a respective zone
```
https://tz.add-to-calendar-technology.com/api/{{zoneName}}.ics
```
With `{{zoneName}}` being your time zone.
So, for New York, this would be [https://tz.add-to-calendar-technology.com/api/America/New_York.ics](https://tz.add-to-calendar-technology.com/api/America/New_York.ics).
**This is case sensitive!**
> [!WARNING]
> Mind that this does not deliver a fully valid ics file, since it only contains the VTIMEZONE part. You will need to combine this with your other event information.
<br /><br />
---
<br />
## 🙌 Contributing
Anyone is welcome to contribute, but mind the [guidelines](.github/CONTRIBUTING.md):
- [Bug reports](.github/CONTRIBUTING.md#bugs)
- [Feature requests](.github/CONTRIBUTING.md#features)
- [Pull requests](.github/CONTRIBUTING.md#pull-requests)
<br />
## 📃 Copyright and License
Copyright (c) [Jens Kuerschner](https://jekuer.com) (Calendarverse GmbH). Licensed under [Apache-2.0](LICENSE).
<br />
## ⚡ Changelog
<details>
<summary>History (without minor changes and fixes)</summary>
- v2.2 : database update (2026b)
- v2.1 : JS to TS migration
- v2.0 : Full refactoring reducing bundle size and easing future updates, using Astro for Demo page
- v1.11 : database update (2025c)
- v1.10 : upgrading to latest vzic improvements
- v1.9 : database update (2025b)
- v1.8 : database update (2024a)
- v1.7 : database update (2023c)
- v1.6 : database update (2022g)
- v1.5 : new dist structure
- v1.4 : further minification via data mapping
- v1.3 : bundle size optimization and API
- v1.2 : providing tzblock as array with separate tzid
- v1.1 : get-offset function
- v1.0 : initial release
</details>
<br />
## 💜 Kudos go to
- The ["Time Zone King"](https://samueli.ucla.edu/time-zone-king-how-one-ucla-computer-scientist-keeps-digital-clocks-ticking/) [Paul Eggert](https://github.com/eggert) for optimizing time zones for the web, ...
- as well as all the contributors at [the official tz repository](https://github.com/eggert/tz).
- The awesome authors of zic, vzic, and [libical](https://github.com/libical/libical/graphs/contributors); mainly Damon Chaplin, [Allen Winter](https://github.com/winterz), and [Ken Murchison](https://github.com/ksmurchison).