AJ ONeal a195b6c5d5 | ||
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.gitignore | ||
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LICENSE | ||
README.md | ||
examples.js | ||
index.html | ||
package.json | ||
test.js | ||
tolocalisostring.js | ||
xtz-preview.png | ||
xtz.js | ||
xtz.min.js |
README.md
xtz.js
A fast, lightweight, zero-dependency library to translate between Time Zones and UTC with native Intl.DateTimeFormat
in ~100 LoC. For Node.js & Browsers.
XTZ is a poor man's Temporal
polyfill, but just for time zones.
Demo: https://therootcompany.github.io/tz.js/
// What's the current time, in ISO format?
TZ.toLocalISOString(new Date()); // "2021-11-07T03:15:59.000-0500"
TZ.timeZone(); // "America/New_York"
// What will the ISO datetime string be
// when it's 3:15am in New York?
//
// (Relative New York time to Absolute UTC Time)
TZ.toOffsetISOString("2021-11-07 03:15:59.000", "America/New_York");
// "2021-11-07T03:15:59.000-0500"
// What time will it be in New York
// when it's 7:15am UTC?
//
// (Absolute UTC time to Relative New York time)
TZ.toTimeZoneISOString("2021-03-14T07:15:59.000Z", "America/New_York");
// "2021-03-14T03:15:59.000-0400"
Features
- Translate a UTC time to a Time Zone
- Translate a Zoned time to UTC
- Handles Daylight Savings, Weird Time Zones, etc...
- Well-tested
npm run test
- Well-tested
- Lightweight (No deps)
- 5kb Source + Comments
- 2.5kb Minified
- <1kb
gzip
d
Compatible with Browsers, and Node.js.
Browsers
<script src="https://unpkg.com/xtz@latest/xtz.min.js"></script>
var TZ = window.XTZ;
Node.js & Webpack
npm install --save xtz
var TZ = require("xtz");
Demo
See https://therootcompany.github.io/tz.js/.
How was this built?
I live-streamed the creation of this entire project.
If you'd like to learn how I did it and what challenges I encountered, you can watch here: https://www.youtube.com/playlist?list=PLxki0D-ilnqa6horOJ2G18WMZlJeQFlAt
(though there have been a few minor updates and bug fixes off-camera)
API
toLocalISOString(dateOrNull)
toTimeZone(utcDate, timeZone)
toTimeZoneISOString(isoString, timeZone)
fromTimeZone(dtString, timeZone)
toOffsetISOString(dtString, timeZone)
toTimeZone(utcDate, timeZone)
Convert UTC into a Target Time Zone
Use ISO timestamps representing the absolute UTC time (with or without offset):
"2021-11-07T08:15:59.000Z"
var utcDate = TZ.toTimeZone("2021-03-14T07:15:59.000Z", "America/New_York");
// {
// year: 2021, month: 2, day: 14,
// hour: 3, minute: 15, second: 59, millisecond: 0,
// offset: -240, timeZoneName: "Eastern Daylight Time"
// }
utcDate.toISOString();
// "2021-03-14T03:15:59.000-0400"
// (same as "2021-11-07T07:15:59.000Z")
Convert directly to an ISO String:
TZ.toTimeZoneISOString("2021-11-07T08:15:59.000Z", "America/New_York");
// "2021-11-07T03:15:59.000-0500"
Or use our bespoke (custom) date object:
var tzDate = TZ.toTimeZone("2021-11-07T08:15:59.000Z", "America/New_York");
You can also use a date object with an absolute UTC time:
var tzDate = TZ.toTimeZone(
new Date("2021-11-07T08:15:59.000Z"),
"America/New_York"
);
console.log(tzDate.toISOString());
// "2021-11-07T03:15:59.000-0500"
Our ISO Strings + Offsets work with JavaScript's native Date object!!
new Date("2021-11-07T03:15:59.000-0500").toISOString());
// "2021-11-07T08:15:59.000Z"
fromTimeZone(dtString, timeZone)
Convert a Target Time Zone into UTC
Use ISO-like timestamps representing the local time in the target time zone:
"2021-11-0 03:15:59.000"
var tzDate = TZ.fromTimeZone("2021-11-07 03:15:59.000", "America/New_York");
// {
// year: 2021, month: 10, day: 7,
// hour: 3, minute: 15, second: 59, millisecond: 0,
// offset: -300, timeZoneName: "Eastern Standard Time"
// }
tzDate.toISOString();
// "2021-11-07T03:15:59.000-0500"
// (same as "2021-11-07T08:15:59.000Z")
Convert directly to an offset ISO String:
TZ.toOffsetISOString("2021-11-07 03:15:59.000", "America/New_York");
// "2021-11-07T03:15:59.000-0500"
Or our bespoke date object:
var utcDate = TZ.fromTimeZone("2021-11-07 03:15:59.000", "America/New_York");
Use a Date as a source time
You can also use a date object as the source time, but the date's UTC time will be treated as relative to time zone rather than absolute (this is a workaround for JavaScript's lack of bi-directional timezone support).
var utcDate = TZ.fromTimeZone(
new Date("2021-11-07T03:15:59.000Z"),
"America/New_York"
);
utcDate.toISOString();
// "2021-11-07T03:15:59.000-0500"
Daylight Savings / Edge Cases
In 2021 Daylight Savings (in the US)
- begins at 2am on March 14th (skips to 3am)
- ends at 2am on November 7th (resets to 1am)
Q: What happens in March when 2am is skipped?
- A: Although 2am is not a valid time, rather than throwing an error this library will resolve to 1am instead, which
is an hour early in real ("tick-tock" or "monotonic") time.
var utcDate = TZ.fromTimeZone("2021-03-14 02:15:59.000", "America/New_York"); utcDate.toISOString(); // "2021-03-14T02:15:59.000-0400" // (same as "2021-03-14T01:15:59.000-0500")
Q: What happens in November when 1am happens twice?
- A: Although both 1ams are distinguishable with ISO offset times, only the first can be resolved from a local time
with this library.
var utcDate = TZ.fromTimeZone("2021-11-07 01:15:59.000", "America/New_York"); utcDate.toISOString(); // "2021-11-07T01:15:59.000-0400", same as "2021-11-07T05:15:59.000Z" // (an hour before the 2nd 1am at "2021-11-07T01:15:59.000-0500")
List of Time Zones
See the Full List of Time Zones on Wikipedia.
Common Zones for Testing:
America/New_York -0500
America/Denver -0700
America/Phoenix -0700 (No DST)
America/Los_Angeles -0800
UTC Z
Australia/Adelaide +0930 (30-min, has DST)
Asia/Kathmandu +0545 (No DST, 45-min)
Asia/Kolkata +0530 (No DST, 30-min)