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