Proper way to parse a date as UTC using date-fns

Question

I have a log file with some timestamps

2020-12-03 08:30:00
2020-12-03 08:40:00
...

I know from the log provider's documentation that the timestamps are written in UTC (although not using ISO format)

Now I want to parse them with date-fns :

const toParse = "2020-12-03 08:40:00"
parse(toParse, 'yyyy-MM-dd HH:mm:ss', new Date()).toISOString()

And because the locale of my computer is in UTC+1 here is what I see:

> "2020-12-03T07:40:00Z"

expected:

> "2020-12-03T08:40:00Z".

Here is the hack I currently use to tell date-fns to parse as UTC :

const toParse = "2020-12-03 08:40:00"
parse(toParse + '+00', 'yyyy-MM-dd HH:mm:ss' + 'X', new Date()).toISOString()

And as expected,

> "2020-12-03T08:40:00Z".

Is there any proper way of doing this using date-fns? Looking for an equivalent to moment's moment.utc()

You may want to take a look at developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/… You know the offset to adjust the stored date to your time zone. Date-fns-tz has support for Intl.DateTimeFormat. — WildWilyWilly
– WildWilyWilly, Commented Dec 7, 2020 at 14:22
Either way you should indicate what timezone a datetime value has. You can sinplify your hack: parseIso(toParse+'Z').toISOString() — Anatoly
– Anatoly, Commented Dec 7, 2020 at 15:37
If "2020-12-03 08:40:00" is parsed as UTC +1, the Z time is 07:40:00Z, not 09:40. :-) — RobG
– RobG, Commented Dec 7, 2020 at 20:29

Bruno Francisco · Accepted Answer · 2021-12-14 20:17:53Z

14

I don't know about "proper", but you can use zonedTimeToUtc to treat a timestamp as having any offset or timezone you like, including UTC, e.g.

// Setup
var {parse} = require('date-fns');
var {zonedTimeToUtc} = require('date-fns-tz');

// Parse an ISO 8601 timestamp recognised by date-fns
let loc = 'UTC';
let s1   = '2020-12-03 08:30:00';
let utcDate =  zonedTimeToUtc(s1, loc);

// Show UTC ISO 8601 timestamp
console.log(utcDate.toISOString()); // "2020-12-03T08:30:00.000Z"

// Parse non–standard format yyyyMMdd
let s2 = '20210119';
let fIn = 'yyyyMMdd';
let d = zonedTimeToUtc(parse(s2, fIn, new Date()), loc);
console.log(d.toISOString()); // "2021-01-19T00:00:00.000Z"```

You can test it at npm.runkit.com/date-fns.

edited Dec 14, 2021 at 20:17

Bruno Francisco

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answered Dec 7, 2020 at 22:54

RobG

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3 Comments

Yann Pellegrini Over a year ago

Thanks that's what I was looking for! However your code does not make use of fIn (fortunately in this example it parses at UTC but the log could have a less friendly format). zonedTimeToUtc(parse(s, fIn, new Date()), loc); works.

RobG Over a year ago

@YannP—yes, if the format isn't one recognised by date-fns then you need to add parse. I find the requirement for a Date to always be passed to parse an inexplicable design decision.

Yann Pellegrini Over a year ago

Totally agree. I had to add a comment to my pull request to explain why it's "needed"...

escapisam · Accepted Answer · 2021-09-22 05:56:07Z

5

I think you are looking for parseJSON, which supports a number of formats (but does not let you specify the source format).

Converts a complete ISO date string in UTC time, the typical format for transmitting a date in JSON, to a JavaScript Date instance.

import { parseJSON } from 'date-fns';
const utcDate = parseJSON('2020-12-03 08:40:00');

// Thu Dec 03 2020 19:40:00 GMT+1100 (Australian Eastern Daylight Time)

answered Sep 22, 2021 at 5:56

escapisam

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3 Comments

strarsis Over a year ago

Yes, parseJSON from date-fns finally worked! I got date strings from SQLite that are in UTC, without explicit timezone. Parsing those date strings using date-fns parse or vanilla JS Date resulted in a modified Date, as a non-UTC timezone was assumed.

Sander van den Akker Over a year ago

This should be the accepted answer, no need for date-fns-tz...

phil Over a year ago

Yes, but you can't use parseJSON('2020-12-03') if you only have a date-only format.

Ken · Accepted Answer · 2021-02-01 21:39:55Z

3

Example of using parse and zonedTimeToUtc

 it('should parse polish date', async () => {
    expect.assertions(1)
    const dateWithoutTime = '29 gru 2003'

    const parsed = parse(dateWithoutTime, 'd LLL yyyy', new Date(), {
      locale: pl,
    })

    const dateUTC = zonedTimeToUtc(parsed, 'UTC')

    expect(dateUTC.toISOString()).toStrictEqual('2003-12-29T00:00:00.000Z')
  })

answered Feb 1, 2021 at 21:39

Ken

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Comments

Jaffadog · Accepted Answer · 2025-06-05 18:50:50Z

0

Use the UTC plugin for date-fns:

<script type="module">
  import {parse} from 'https://cdn.jsdelivr.net/npm/[email protected]/+esm'
  import {utc} from 'https://cdn.jsdelivr.net/npm/@date-fns/[email protected]/+esm'
 
  console.log(parse("2020-12-03 08:40:00", "yyyy-MM-dd HH:mm:ss", new Date(), {
    in: utc
  }));
</script>

answered Jun 5 at 18:50

Jaffadog

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