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how to define a specifc date notation in javascript using Intl.DateTimeFormat [duplicate]

This question already has answers here:
How do I format a date in JavaScript?
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Closed last month.
Its so surprising to see JavaScript not having a easy to use format for dates.
I'm trying do get this format (example in python)
>>> datetime.now().strftime("%Y%m%d")
'20221228'
I did find that Intl.DateTimeFormat can do some format the Date() objects. But from the docs I don't see how to make a custom format out of this.
There are canned formats en-US en-GB which it would be nice to define a format.
> var dateOptions = {year:'numeric', month:'numeric', day:'numeric'}
> console.log( Intl.DateTimeFormat('en-GB', dateOptions).format(Date.now()))
28/12/2022
> console.log( Intl.DateTimeFormat('en-US', dateOptions).format(Date.now()))
12/28/2022
It partially controls formatting but does anyone know how to actually control the output format with Intl.DateTimeFormat to output YYYYMMDD?

Based upon #HereticMonkey here is what I hacked to solve it with the core JavaScript. Cant imagine why Intl.DateTimeFormat is not capable of user defined formatting. This is basic needs.
function toYYYYMMDD(date){
let dateFields = {}
let options = {
year: 'numeric',
month: 'numeric',
day: 'numeric'
}
let formatDate = new Intl.DateTimeFormat('en-US', options )
formatDate.format(date)
let parts = formatDate.formatToParts()
for (var i = 0; i < parts.length; i++) {
dateFields[parts[i].type] = parts[i].value;
}
return dateFields.year + dateFields.month + dateFields.day
}
toYYYYMMDD(new Date())
'20221228'
EDIT this way is also lame because it cant convert time to localtime and its way too much code.
i finally went with luxon which is way easy.
luxon.DateTime.local(2022, 12, 28, 08, 00, 00).toFormat("yyyyMMdd")
"20221228"
luxon.DateTime.local(2022, 12, 28, 18, 00, 00).toFormat("[yyyyMMMdd] HH:mm")
"[2022Dec28] 18:00"
And time 24 or 12 hour
luxon.DateTime.local(2022, 12, 28, 18, 00, 00).toFormat("hh:mm a")
"06:00 PM"
luxon.DateTime.local(2022, 12, 28, 18, 00, 00).toFormat("HH:mm")
"18:00"

Format date in JS, and keep the date format for different locales

I have a setting for a date format that looks like:
const shortMonth12 = {
year: 'numeric', month: 'short', day: 'numeric', hour: '2-digit', minute: '2-digit', hour12: 'true' };
Which will give me the following date format:
console.log(date.toLocaleString('en-US', shortMonth12)) // "Mar 28, 2022, 01:55 PM"
Great, it works and we have the date format we want. We dont want to change it.
But we also want to also translate the month name. But problem is the format itself also changes when providing another locale. For example:
console.log(date.toLocaleString('sv-SE', shortMonth12)); // "28 mars 2022 01:55 em"
So, we want to use the locales to translate the months, but also keep the formatting the same. Is it possible the way the implementation looks like?

So, we want to use the locales to translate the months, but also keep the formatting the same.
No, since toLocaleString uses the provided locale to format the date, the outcome is depending on the locale.
If you use 2 different locale's that have different date formats, like en-US and sv-SE you'll get different formats, as intended.
en-US: Mar 28, 2022, 02:19 PM
sv-SE: 28 mars 2022 02:19 em
You can get the desired outcome by creating the string manual, this requires some more logic and goes against the idea behind toLocaleString.
Use the functions like toLocaleTimeString and getFullYear to create variables based on the locale, then create a string with the desired format, for example:
const customFormat = (date, locale) => {
let d = date.getDate(),
m = date.toLocaleString(locale, { month: 'long' }),
y = date.getFullYear(),
t = date.toLocaleTimeString(locale, { hour: '2-digit', minute: '2-digit', hour12: 'true' });
return `${d} ${m}, ${y}, ${t}`;
}
const d = new Date();
const d1 = customFormat(d, 'en-US');
const d2 = customFormat(d, 'sv-SE');
console.log(d1); // 28 March, 2022, 02:25 PM
console.log(d2); // 28 mars, 2022, 02:25 em

How do I remove the Date part from JavaScript date?

I have a date 12/19/2016 8:54 in a variable. I want the value of only the time without the date. How do I do this?
Examples:
Input: 12/19/2016 8:54 Output: 8:54
Input: 2/2/2018 11:30 Output: 11:30
The only way I see this is string manipulation, which I believe is a bad idea.

you can use split method.
const time = '12/19/2016 8:54'.split(" ")[1];

If your date variable is an actual Date object then you can use Intl.DateTimeFormat to get it formatted any way you want. Here is how:
var d = new Date(2016, 11, 19, 8, 54);
console.log(d); // If you are not in UTC then this will show the Date with timezone adjustment applied
var hourAndMinute = { hour: "numeric", minute: "numeric" };
var formatter = new Intl.DateTimeFormat("en-GB", hourAndMinute);
var result = formatter.format(d); // This does the reverse timezone adjustment
console.log(result);

How to parse timestamp to JSON in NodeJS?

I wanna create a NodeJS application with an API which provides a current timestamp in JSON-format. This JSON should be called when the user calls the /api/current_time path.
The format could be look like this:
{
"date" : 24,
"month": 12,
"year" : 2020,
"hours" : 10,
"minutes" : 10,
"seconds" : 54
}
I would work with Date-Object. How can I parse these variables into a new JSON-File? The values should be refreshing when the user presses F5.
How can I realize this?
Thanks.

If I understood you correctly, you need to return a JSON when the /api/current_time path gets called. I suppose you mean JSON object instead of "JSON-File". If so, something as simple as:
const date = new Date();
const dateRepresentation = {
year: date.getUTCFullYear(),
month: date.getUTCMonth() + 1,
day: date.getUTCDate(),
hours: date.getUTCHours(),
minutes: date.getUTCMinutes(),
seconds: date.getUTCSeconds()
};
return JSON.stringify(dateRepresentation); // or simply - return dateRepresentation;
The returned date will be in UTC.

You Can also use moment.
I am reusing zhulien example with moment :
const currentDate = moment(); //get the current Timestamp.
return dateObject = {
seconds = currentDate.format('ss'),
minutes = currentDate.format('mm'),
hours = currentDate.format('hh'),
year = currentDate.format('YYYY'),
month = currentDate.format('MM'),
day = currentDate.format('DD')
};

Display date/time in user's locale format and time offset

I want the server to always serve dates in UTC in the HTML, and have JavaScript on the client site convert it to the user's local timezone.
Bonus if I can output in the user's locale date format.

Seems the most foolproof way to start with a UTC date is to create a new Date object and use the setUTC… methods to set it to the date/time you want.
Then the various toLocale…String methods will provide localized output.
Example:
// This would come from the server.
// Also, this whole block could probably be made into an mktime function.
// All very bare here for quick grasping.
d = new Date();
d.setUTCFullYear(2004);
d.setUTCMonth(1);
d.setUTCDate(29);
d.setUTCHours(2);
d.setUTCMinutes(45);
d.setUTCSeconds(26);
console.log(d); // -> Sat Feb 28 2004 23:45:26 GMT-0300 (BRT)
console.log(d.toLocaleString()); // -> Sat Feb 28 23:45:26 2004
console.log(d.toLocaleDateString()); // -> 02/28/2004
console.log(d.toLocaleTimeString()); // -> 23:45:26
Some references:
toLocaleString
toLocaleDateString
toLocaleTimeString
getTimezoneOffset

You can do it with moment.js (deprecated in 2021)
It's best to parse your date string from UTC as follows (create an ISO-8601 compatible string on the server to get consistent results across all browsers):
var m = moment("2013-02-08T09:30:26Z");
Now just use m in your application, moment.js defaults to the local timezone for display operations. There are many ways to format the date and time values or extract portions of it.
You can even format a moment object in the users locale like this:
m.format('LLL') // Returns "February 8 2013 8:30 AM" on en-us
To transform a moment.js object into a different timezone (i.e. neither the local one nor UTC), you'll need the moment.js timezone extension. That page has also some examples, it's pretty simple to use.
Note: Moment JS recommends more modern alternatives, so it is probably not a good choice for new projects.

You can use new Date().getTimezoneOffset()/60 for the timezone. There is also a toLocaleString() method for displaying a date using the user's locale.
Here's the whole list: Working with Dates

In JS there are no simple and cross platform ways to format local date time, outside of converting each property as mentioned above.
Here is a quick hack I use to get the local YYYY-MM-DD. Note that this is a hack, as the final date will not have the correct timezone anymore (so you have to ignore timezone). If I need anything else more, I use moment.js.
var d = new Date();
d = new Date(d.getTime() - d.getTimezoneOffset() * 60000)
var yyyymmdd = t.toISOString().slice(0, 10);
// 2017-05-09T08:24:26.581Z (but this is not UTC)
The d.getTimezoneOffset() returns the time zone offset in minutes, and the d.getTime() is in ms, hence the x 60,000.

2021 - you can use the browser native Intl.DateTimeFormat
const utcDate = new Date(Date.UTC(2020, 11, 20, 3, 23, 16, 738));
console.log(new Intl.DateTimeFormat().format(utcDate));
// expected output: "21/04/2021", my locale is Switzerland
Below is straight from the documentation:
const date = new Date(Date.UTC(2020, 11, 20, 3, 23, 16, 738));
// Results below assume UTC timezone - your results may vary
// Specify default date formatting for language (locale)
console.log(new Intl.DateTimeFormat('en-US').format(date));
// expected output: "12/20/2020"
// Specify default date formatting for language with a fallback language (in this case Indonesian)
console.log(new Intl.DateTimeFormat(['ban', 'id']).format(date));
// expected output: "20/12/2020"
// Specify date and time format using "style" options (i.e. full, long, medium, short)
console.log(new Intl.DateTimeFormat('en-GB', { dateStyle: 'full', timeStyle: 'long' }).format(date));
// Expected output "Sunday, 20 December 2020 at 14:23:16 GMT+11"

Once you have your date object constructed, here's a snippet for the conversion:
The function takes a UTC formatted Date object and format string.
You will need a Date.strftime prototype.
function UTCToLocalTimeString(d, format) {
if (timeOffsetInHours == null) {
timeOffsetInHours = (new Date().getTimezoneOffset()/60) * (-1);
}
d.setHours(d.getHours() + timeOffsetInHours);
return d.strftime(format);
}

// new Date(year, monthIndex [, day [, hours [, minutes [, seconds [, milliseconds]]]]])
var serverDate = new Date(2018, 5, 30, 19, 13, 15); // just any date that comes from server
var serverDateStr = serverDate.toLocaleString("en-US", {
year: 'numeric',
month: 'numeric',
day: 'numeric',
hour: 'numeric',
minute: 'numeric',
second: 'numeric'
})
var userDate = new Date(serverDateStr + " UTC");
var locale = window.navigator.userLanguage || window.navigator.language;
var clientDateStr = userDate.toLocaleString(locale, {
year: 'numeric',
month: 'numeric',
day: 'numeric'
});
var clientDateTimeStr = userDate.toLocaleString(locale, {
year: 'numeric',
month: 'numeric',
day: 'numeric',
hour: 'numeric',
minute: 'numeric',
second: 'numeric'
});
console.log("Server UTC date: " + serverDateStr);
console.log("User's local date: " + clientDateStr);
console.log("User's local date&time: " + clientDateTimeStr);

Here's what I've used in past projects:
var myDate = new Date();
var tzo = (myDate.getTimezoneOffset()/60)*(-1);
//get server date value here, the parseInvariant is from MS Ajax, you would need to do something similar on your own
myDate = new Date.parseInvariant('<%=DataCurrentDate%>', 'yyyyMMdd hh:mm:ss');
myDate.setHours(myDate.getHours() + tzo);
//here you would have to get a handle to your span / div to set. again, I'm using MS Ajax's $get
var dateSpn = $get('dataDate');
dateSpn.innerHTML = myDate.localeFormat('F');

The .getTimezoneOffset() method reports the time-zone offset in minutes, counting "westwards" from the GMT/UTC timezone, resulting in an offset value that is negative to what one is commonly accustomed to. (Example, New York time would be reported to be +240 minutes or +4 hours)
To the get a normal time-zone offset in hours, you need to use:
var timeOffsetInHours = -(new Date()).getTimezoneOffset()/60
Important detail:
Note that daylight savings time is factored into the result - so what this method gives you is really the time offset - not the actual geographic time-zone offset.

With date from PHP code I used something like this..
function getLocalDate(php_date) {
var dt = new Date(php_date);
var minutes = dt.getTimezoneOffset();
dt = new Date(dt.getTime() + minutes*60000);
return dt;
}
We can call it like this
var localdateObj = getLocalDate('2015-09-25T02:57:46');

I mix the answers so far and add to it, because I had to read all of them and investigate additionally for a while to display a date time string from db in a user's local timezone format.
The datetime string comes from a python/django db in the format: 2016-12-05T15:12:24.215Z
Reliable detection of the browser language in JavaScript doesn't seem to work in all browsers (see JavaScript for detecting browser language preference), so I get the browser language from the server.
Python/Django: send request browser language as context parameter:
language = request.META.get('HTTP_ACCEPT_LANGUAGE')
return render(request, 'cssexy/index.html', { "language": language })
HTML: write it in a hidden input:
<input type="hidden" id="browserlanguage" value={{ language }}/>
JavaScript: get value of hidden input e.g. en-GB,en-US;q=0.8,en;q=0.6/ and then take the first language in the list only via replace and regular expression
const browserlanguage = document.getElementById("browserlanguage").value;
var defaultlang = browserlanguage.replace(/(\w{2}\-\w{2}),.*/, "$1");
JavaScript: convert to datetime and format it:
var options = { hour: "2-digit", minute: "2-digit" };
var dt = (new Date(str)).toLocaleDateString(defaultlang, options);
See: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleDateString
The result is (browser language is en-gb): 05/12/2016, 14:58

The best solution I've come across is to create [time display="llll" datetime="UTC TIME" /] Tags, and use javascript (jquery) to parse and display it relative to the user's time.
http://momentjs.com/ Moment.js
will display the time nicely.

You could use the following, which reports the timezone offset from GMT in minutes:
new Date().getTimezoneOffset();
Note :
- this function return a negative number.

getTimeZoneOffset() and toLocaleString are good for basic date work, but if you need real timezone support, look at mde's TimeZone.js.
There's a few more options discussed in the answer to this question

To convert date to local date use toLocaleDateString() method.
var date = (new Date(str)).toLocaleDateString(defaultlang, options);
To convert time to local time use toLocaleTimeString() method.
var time = (new Date(str)).toLocaleTimeString(defaultlang, options);

A very old question but perhaps this helps someone stumbling into this.
Below code formats an ISO8601 date string in a human-friendly format corresponding the user's time-zone and locale. Adapt as needed. For example: for your app, are the hours, minutes, seconds even significant to display to the user for dates more than 1 days, 1 week, 1 month, 1 year or whatever old?
Also depending on your application's implementation, don't forget to re-render periodically.
(In my code below at least every 24hours).
export const humanFriendlyDateStr = (iso8601) => {
// Examples (using Node.js):
// Get an ISO8601 date string using Date()
// > new Date()
// 2022-04-08T22:05:18.595Z
// If it was earlier today, just show the time:
// > humanFriendlyDateStr('2022-04-08T22:05:18.595Z')
// '3:05 PM'
// If it was during the past week, add the day:
// > humanFriendlyDateStr('2022-04-07T22:05:18.595Z')
// 'Thu 3:05 PM'
// If it was more than a week ago, add the date
// > humanFriendlyDateStr('2022-03-07T22:05:18.595Z')
// '3/7, 2:05 PM'
// If it was more than a year ago add the year
// > humanFriendlyDateStr('2021-03-07T22:05:18.595Z')
// '3/7/2021, 2:05 PM'
// If it's sometime in the future return the full date+time:
// > humanFriendlyDateStr('2023-03-07T22:05:18.595Z')
// '3/7/2023, 2:05 PM'
const datetime = new Date(Date.parse(iso8601))
const now = new Date()
const ageInDays = (now - datetime) / 86400000
let str
// more than 1 year old?
if (ageInDays > 365) {
str = datetime.toLocaleDateString([], {
year: 'numeric',
month: 'numeric',
day: 'numeric',
hour: 'numeric',
minute: 'numeric',
})
// more than 1 week old?
} else if (ageInDays > 7) {
str = datetime.toLocaleDateString([], {
month: 'numeric',
day: 'numeric',
hour: 'numeric',
minute: 'numeric',
})
// more than 1 day old?
} else if (ageInDays > 1) {
str = datetime.toLocaleDateString([], {
weekday: 'short',
hour: 'numeric',
minute: 'numeric',
})
// some time today?
} else if (ageInDays > 0) {
str = datetime.toLocaleTimeString([], {
timeStyle: 'short',
})
// in the future?
} else {
str = datetime.toLocaleDateString([], {
year: 'numeric',
month: 'numeric',
day: 'numeric',
hour: 'numeric',
minute: 'numeric',
})
}
return str
}
Inspired from: https://alexwlchan.net/2020/05/human-friendly-dates-in-javascript/
Tested using Node.js

Don't know how to do locale, but javascript is a client side technology.
usersLocalTime = new Date();
will have the client's time and date in it (as reported by their browser, and by extension the computer they are sitting at). It should be trivial to include the server's time in the response and do some simple math to guess-timate offset.