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date-fns/format always takes local timezone

From below code:
const dateString = '1994-09-15T12:00:00-03:00';
const parsedDate = parseISO(dateString)
const dateFormat = 'MM-dd-yyyy HH:mm:ss xxx'
console.log(format(parsedDate, dateFormat, { }))
I expect:
09-15-1994 20:30:00 -03:00 But i get 09-15-1994 20:30:00 +05:30 as my local timezone is +05:30
What am i missing here?

The parseDate() creates a date based on GMT, e.g. is adjusted by 3h based on your input '1994-09-15T12:00:00-03:00'.
The format() function with xxx formats local time without the Z, such as -08:00, +05:30, +00:00. If you want to format with GMT string, specify OOOO, which will give you something like GMT-08:00, GMT+05:30, or GMT+00:00, which again has the offset adjusted based on your browser's time zone.
See Time-Zones docs below if you want to format to a time zone other than your browser's one, such as GMT-03:00.
Docs:
ISO 8601: https://en.wikipedia.org/wiki/ISO_8601
parseDate(): https://date-fns.org/v2.29.2/docs/parseISO
format(): https://date-fns.org/v2.29.2/docs/format
Time-Zones: https://date-fns.org/v2.29.2/docs/Time-Zones

Creating a Date is adding automatically one hour to my input date

let's say I have this date as input :
var _dateA = 2018-11-15T11:13:26.687Z
If I'm doing, whatever,
var _dateB = new Date(_date)
or
var _dateB = moment(_date)
I get this as result ==>
_dateB = Thu Nov 15 2018 12:13:26 GMT+0100 (heure normale d’Europe centrale)
I understood that there's timezone trouble, but how can I get a Date object or Moment object, without having this one hour more?
Wanted result => Thu Nov 15 2018 11:13:26 GMT+0100
Current result => Thu Nov 15 2018 12:13:26 GMT+0100

You need to use Date.toUTCString() that converts date to string, using the UTC time zone
var _dateA = '2018-11-15T11:13:26.687Z';
var _dateB = new Date(_dateA);
console.log(_dateB.toUTCString());

When you "output" a Date object via console.log(), alert(), etc the toString() method is used by default, converting the date object to a local timezone string for display (which is why you are seeing your date in your local time).
Parsing date strings with the Date constructor is not recommended (although, I suspect that most browsers probably handle ISO 8601 dates, like the one in your question, fairly well) - see the dateString parameter note here. So, if you need to construct a date object as well as output a date string, then you could parse the ISO 8601 string with split() using a regex character set for multiple delimiters, then construct a UTC date object with new Date(Date.UTC(...)). You could also do this with moment.js but the below should illustrate what is happening in a bit more detail.
For example:
const text = '2018-11-15T11:13:26.687Z'
const [y, m, d, hh, mm, ss, ms] = text.split(/[-T:.Z]/);
const date = new Date(Date.UTC(y, m - 1, d, hh, mm, ss, ms));
console.log(date.toLocaleString()); // date string in local timezone
console.log(date.toUTCString()); // UTC date string
console.log(JSON.stringify(date)); // ISO 8601 date string in most browsers

How to convert date time from ISO Format to UTC time zone?

I am using moment.js, and I want to convert from ISO Format date time to UTC time zone.
I can convert from local time to UTC+ISOformat, but I am not able to convert ISO format to UTC time zone.
Input:
2018-03-22T00:00:00Z
Expected output:
date should be in UTC time zone. If I calculate the it should be:
22018-03-21T18:30:00Z
First I want to convert into ISO, After that convert into UTC**.
Not able to Converted local date time to ISO then UTC
We can convert into string, But from ISO format can convert or not?
Fox example: I want to convert ISODATE(2018-03-22T00:00:00Z) into UTC time zone.
function toISO(dt) {
return moment(dt).format("YYYY-MM-DDTHH:mm:ss") + "Z";
}
var date = new Date();
var isoDate= toISO(date)
Direct we can convert
function toISOWithUtc(dt) {
return moment(dt).utc().format("YYYY-MM-DDTHH:mm:ss") + "Z";
}
var date = new Date();
toISO(date)

Both 2018-03-22T00:00:00Z and 2018-03-21T18:30:00Z already are in UTC.
Note the Z in the end? This means that the date is in UTC. It's not a hardcoded letter that you can just append to the end - it has a specific meaning, it tells that the date/time is in UTC.
If you want to convert that UTC date to another timezone (I'm guessing that's what you want), you can use moment.tz:
// convert UTC 2018-03-22T00:00:00Z to Asia/Kolkata timezone
moment.tz('2018-03-22T00:00:00Z','Asia/Kolkata')
Just change the timezone name to the one you want to convert.
And calling format() will give you the converted date/time in ISO8601 format:
moment.tz('2018-03-22T00:00:00Z','Asia/Kolkata').format() // 2018-03-22T05:30:00+05:30
Note that the offset changed from Z to +05:30. This means that the date/time above is 5 hours and 30 minutes ahead UTC, which is the result of converting 2018-03-22T00:00:00Z to Kolkata's timezone.
Note: I think you're mistaking the concepts here.
UTC is a time standard. It defines things like the current date/time accross the world, it uses atomic clocks to make sure everybody on Earth are synchronized, and timezones are all based on offsets from UTC.
ISO8601 is a standard for exchanging date/time-related data. It defines formats (text representations of dates). A date/time can be in ISO format, regardless of being in UTC or not.
That's why "convert from UTC to ISO" (or vice-versa) makes no sense at all.

Any way to parse a time string using Moment.js but ignore timezone info?

Given the volume of Timezone questions, I would have thought to be able to find the answer to this issue, but haven't had any success.
Is there a way using moment.js to parse an ISO-8601 string but have it parsed in my local timzeone? Essentially I want to ignore the timezone information that is supplied in the ISO string.
For example, if I am in EDT timezone:
var x = moment( "2012-12-31T00:00:00+0000" );
will give me:
"2012-12-30T19:00:00-5000"
I'm looking to ignore the timezone info and just have it give me a moment equivalent of "2012-12-31T00:00:00-5000" local time (EDT).

I don't think you really want to ignore the offset. That would ultimately just be replacing the offset you provided with one from your local time zone - and that would result in a completely different moment in time.
Perhaps you are just looking for a way to have a moment retain the time zone it was given? If so, then use the moment.parseZone function. For example:
var m = moment.parseZone("2012-12-31T00:00:00+0000");
var s = m.format(); // "2012-12-31T00:00:00+00:00"
You could also achieve this with moment.utc. The difference is that moment.parseZone will retain whatever offset you give it, while moment.utc will adjust to UTC if you give it a non-zero offset.

I solved this by supplying a format as the second argument, and using Moment's method of escaping characters, and wrapped square brackets around the timezone.
moment("2016-01-01T05:00:00-05:00", "YYYY-MM-DDTHH:mm:ss[Z]").startOf("hour").format()
This will still create moment objects using your local time zone, but it won't do any sort of auto-timezone calculation. So the above example will give you 5am regardless of timezone supplied.

I know I'm late to the party, I had the same question and my searches didn't bring me any closer. I broke down and read the documentation and there is an option in moment for a String + Format:
String + Format docs
moment(String, String);
moment(String, String, String);
moment(String, String, Boolean);
moment(String, String, String, Boolean);
and more words, then this:
Unless you specify a time zone offset, parsing a string will create a date in the current time zone.
moment("2010-10-20 4:30", "YYYY-MM-DD HH:mm"); // parsed as 4:30 local time
moment("2010-10-20 4:30 +0000", "YYYY-MM-DD HH:mm Z"); // parsed as 4:30 UTC
The part that gave me pause was the example that was used to parse local time omitted the +0000, which lead me to think the input string needed to have that removed, but it doesn't.
example:
var time = "2012-12-31T00:00:00+0000";
var x = moment(time); // Sun Dec 30 2012 19:00:00 GMT-0500
var y = moment(time,'YYYY-MM-DD'); //Mon Dec 31 2012 00:00:00 GMT-0500

You can ignore the browser's timezone completely by creating a new moment using moment.utc() instead of moment().
For example, if you are trying to work purely with a UTC date/time of the browser's current time but want to discard its timezone data, you can recreate the browser's current time into a UTC format using the following:
let nowWithTimezone = moment();
let nowInUtc = moment.utc(nowWithTimezone.format('MM/DD/YYYY HH:mm'), 'MM/DD/YYYY HH:mm');
Further documentation on moment.utc(): https://momentjs.com/docs/#/parsing/utc/

If you know for sure your input string is in the ISO-8601 format, you could just strip off the last 5 digits and use that in the Moment constructor.
var input = "2012-12-31T00:00:00+0000"
input = input.substring(0, input.length-5)
moment(input).toString()
> "Mon Dec 31 2012 00:00:00 GMT-0600"

There are valid reasons to do what the OP is asking for. The easiest way to do this with Moment is using its parseZone(date) method. No futzing around with string manipulation or multiple calls. It effectively parses the date string as though it were in the browser's local time zone.

This is difficult task to do with MomentJS, it will basically depend as well on your current timezone.
Documentation as well is vague for this specific task, the way I solved the issue on my side was by adding hours to the date before converting it to JSON format.
var dt = moment("Sun Sep 13 2015 00:00:00 GMT-0400", "ddd MMM DD YYYY HH:mm:ss GMT-0400", false);
var date = dt.add(2, 'hour').toJSON();
console.log(date); //2015-09-13T00:00:00.000Z

Momentjs default logic will format the given time with local timezone. To format original date, I wrote a function:
https://github.com/moment/moment/issues/2788#issuecomment-321950638

Use moment.parseZone to convert without taking into account the timezone.
const moment = require('moment')
const dateStr = '2020-07-21T10:00:00-09'
const date = moment.parseZone(dateStr)
console.log(date.format('MM-DD-YY HH:mm A')) // 07-21-20 10:00 AM
Try here link to docs

The best way is to use:
dt = moment("Wed Sep 16 2015 18:31:00 GMT-0400", "ddd MMM DD YYYY HH:mm:ss GMT-0400",true);
And to display convert again to desired timezone:
dt.utcOffset("-04:00").toString()
output > Wed Sep 16 2015 18:31:00 GMT-0400

How to assume local time zone when parsing ISO 8601 date string?

I have a ISO date string as below
var startTimeISOString = "2013-03-10T02:00:00Z";
when I convert it to date object in javascript using below code, it returns
var startTimeDate = new Date(startTimeISOString);
output is
Date {Sun Mar 10 2013 07:30:00 GMT+0530 (India Standard Time)}
It sure converts the ISOString to date but it converts to local time since new Date() is client dependent. How to just convert iso date time string to date and time but not to local date-time..?
Thanks

According to MDN:
Differences in assumed time zone
Given a date string of "March 7, 2014", parse() assumes a local time
zone, but given an ISO format such as "2014-03-07" it will assume a
time zone of UTC. Therefore Date objects produced using those strings
will represent different moments in time unless the system is set with
a local time zone of UTC. This means that two date strings that appear
equivalent may result in two different values depending on the format
of the string that is being converted (this behavior is changed in
ECMAScript ed 6 so that both will be treated as local).
I have done like this and am now getting the exact time which is inside the ISO date string instead of the local time
var startTimeISOString = "2013-03-10T02:00:00Z";
var startTime = new Date(startTimeISOString );
startTime = new Date( startTime.getTime() + ( startTime.getTimezoneOffset() * 60000 ) );
This will give the same date time inside iso date string , the output here is
o/p
Date {Sun Mar 10 2013 02:00:00 GMT+0530 (India Standard Time)}

To sum up the conversation from tracevipin's post:
All Date objects are based on a time value that is milliseconds since 1970-01-01T00:00:00Z so they are UTC at their core. This is different to UNIX, which uses a value that is represents seconds since the same epoch.
The Date.prototype.toString method returns an implementation dependent string that represents the time based on the system settings and timezone offset of the client (aka local time).
If a UTC ISO8601 time string is required, the Date.prototype.toISOString method can be used. It's quite easy to write a "shim" for this methods if required.
Lastly, do not trust Date.parse to parse a string. Support for an ISO8601 format UTC string is specified in ES5, however it's not consistently implemented across browsers in use. It is much better to parse the string manually (it's not hard, there are examples on SO of how to do it) if wide browser support is required (e.g. typical web application).
Simple ISO8601 UTC time stamp parser:
function dateObjectFromUTC(s) {
s = s.split(/\D/);
return new Date(Date.UTC(+s[0], --s[1], +s[2], +s[3], +s[4], +s[5], 0));
}
and here's a shim for toISOString:
if (typeof Date.prototype.toISOString != 'function') {
Date.prototype.toISOString = (function() {
function z(n){return (n<10? '0' : '') + n;}
function p(n){
n = n < 10? z(n) : n;
return n < 100? z(n) : n;
}
return function() {
return this.getUTCFullYear() + '-' +
z(this.getUTCMonth() + 1) + '-' +
z(this.getUTCDate()) + 'T' +
z(this.getUTCHours()) + ':' +
z(this.getUTCMinutes()) + ':' +
z(this.getUTCSeconds()) + '.' +
p(this.getUTCMilliseconds()) + 'Z';
}
}());
}

This happens because date is printed using toString method which by default returns the date and time in local timezone. The method toUTCString will give you the string you need.
Date actually keeps the date as unix time in milliseconds and provides methods to manipulate it.

In vanilla javascript there isn't a way to create a date that assumes the local time of the ISO formatted string you give it. Here's what happens when you pass an ISO 8601 formatted string to javascript. I'm going to use a non UTC time as it illustrates the problem better than using an ISO formatted string:
var startTime = new Date("2013-03-10T02:00:00+06:00"). Note this could also be 2013-03-10T02:00:00Z or any other ISO-formatted string.
read the time, apply the offset and calculate milliseconds since 1970-01-01T00:00:00Z
You now have only milliseconds - you have lost all timezone info. In this case 1362859200000
All functions, apart from the ones that give you a UTC representation of that number, will use the timezone of the computer running the code to interpret that number as a time.
To do what the original poster wants, you need to.
parse the ISO string, interpret the offset ('Z' or '+06:00') as the timezone offset
store the timezone offset
calculate and store the ms since epoch, using the offset timezone offset
hold that offset
whenever attempting to make a calculation or print the date, apply the timezone offset.
This isn't trivial, and requires a complete interpretation of the 8601 spec. Way too much code to put here.
This is exactly what moment.js is designed to do. I strongly recommend using it. Using moment.js:
moment("2013-03-10T02:00:00Z").format()
"2013-03-10T02:00:00Z"
this will result in printing the ISO time of the original string, preserving the offset.

you can try moment js library https://momentjs.com
For my case, I had 2022-10-17T01:00:00 on my database. SO I need to format it to the 01:00:00 AM.
So here was my solution.
var date = "2022-10-17T01:00:00"
var timeFormat = moment(date ).format('HH:mm A');
output: 01:00:00 AM

it will return ISOdate
var getDate = () => {
var dt = new Date();
var off = dt.getTimezoneOffset() * 60000
var newdt = new Date(dt - off).toISOString()
return newdt.slice(0, 19)
}
Output