Express time as CST in javascript - date-fns

Express time as CST in javascript - date-fns - javascript

I am using date-fns to format dates
If I pass a date that ends in Z, it knows that it is UTC, and I can format(date, "yyyy-MM-dd") and it will be in local computer time.
If the date I want to express in local computer time is originally CST, is there something to add at the end instead of the Z, that will be understood by the format function as a CST date?
Sorry if this is a bad question
Edit: is there a way to do zonedTimeToUtc(myDate, 'UTC-6') in date-fns? (instead of using a time zone name)

If you have a string that you always want parsed as CST (US central standard time) using date-fns, you can include date-fns-tz and set the timezone when parsing (I've assumed an ISO 8601 loose format without the timezone). Note that to avoid DST, you have to pick a location that is UTC-6 all year round, e.g. Canada/Saskatchewan.
// Setup
var {parse} = require('date-fns');
var {zonedTimeToUtc, utcToZonedTime, format } = require('date-fns-tz');
// Parse using location for offset
let loc = 'Canada/Saskatchewan';
let s = '2020-08-14 13:05:52';
let fIn = 'yyyy-MM-dd HH:mm:ss';
let utcDate = zonedTimeToUtc(s, loc);
// Show local equivalent
console.log(utcDate);
This leaves you somewhat at the mercy of the administrators of Saskatchewan, who might change the offset or introduce DST. An alternative is to append the exact offset you want to the timestamp and include it in the parse tokens:
// Parse using string for offset
let tz = '-06';
let utcDate2 = parse(s + ' ' + tz, fIn + ' X', new Date());
// Show local equivalent, should be same as above
console.log(utcDate2);
The advantage of the second method is that it doesn't require date-fns-tz and you aren't beholden to historic or future changes to Saskatchewan's offset (or that of any other IANA location).
Apparently there is a UTC module in development that will allow setting specific offsets like -6 rather than using IANA locations (can't find a link to that comment atm).
At this point the string has been parsed as GMT-6, but is still just a plain Date (i.e. just a time value with no idea of the timezone that was associated with the original string).
Once you have the date you can then show it as CST for output. To use an IANA location for the offset in call to format, you have to use format from date-fns-tz, not plain date-fns, otherwise it will just use the host system offset.
Note that the value in the format call is just setting the value to use for the offset string, it doesn't do anything to the actual date and time, that adjustment has already been applied by utcToZonedTime.
// Adjust to CST
let dCST = utcToZonedTime(utcDate2, loc);
// Format strings:
let fOut1 = 'yyyy-MM-dd HH:mm:ss XXX'; // -0600
let fOut2 = 'yyyy-MM-dd HH:mm:ss z'; // CST
// Format using location
console.log(format(dCST, fOut1, {timeZone: loc}));
console.log(format(dCST, fOut2, {timeZone: loc}));
I prefer the -0600 version as it avoids questions of whether DST is observed or not (and is really what the code is doing). Also, in the "z" version you might get the offset or the timezone name (probably depending on the host default language and location, which is a quirk of date-fns-tz using Intl.DateTimeFormat I think).
You can also manually add the timezone using a format string like:
let fOut = 'yyyy-MM-dd HH:mm:ss \'-0600\'';
which will produce an output like:
"2020-08-14 13:05:52 GMT-0600"
I don't think there is any way to set a specific offset like "-0600" for both parsing and formatting without including it in the call. I think moment.js and luxon allow it.
For completeness, here's some code you can run at npm.runkit.com since there's no CDN for the current date-fns version to allow the code to run here.
var {parse} = require('date-fns');
var {zonedTimeToUtc, utcToZonedTime, format } = require('date-fns-tz');
// Parse using location for offset
let loc = 'Canada/Saskatchewan';
let s = '2020-08-14 13:05:52';
let fIn = 'yyyy-MM-dd HH:mm:ss';
let utcDate = zonedTimeToUtc(s, loc);
// Show local equivalent
console.log(utcDate);
// Parse using string for offset
let tz = '-06';
let utcDate2 = parse(s + ' ' + tz, fIn + ' X', new Date());
// Show local equivalent, should be same as above
console.log(utcDate2);
// Format using location:
let fOut1 = 'yyyy-MM-dd HH:mm:ss XXX'; // -0600
let fOut2 = 'yyyy-MM-dd HH:mm:ss z'; // CST
let dCST = utcToZonedTime(utcDate2, loc);
console.log(format(dCST, fOut1, {timeZone: loc}));
console.log(format(dCST, fOut2, {timeZone: loc}));

Try using moment libraries to solve your time problems: moment.js, and its complement moment-timezone.js
To output the current time converted to CST timezone:
moment().tz('America/Chicago').format('hh:mm:ss z')
06:43:34 CST
moment().tz('America/Chicago').format('hh:mm:ss z Z')
06:43:35 CST -06:00
moment().tz('America/Chicago').format()
2020-08-13T15:52:09-06:00
Or maybe use a function as below:
const calcTime = (cityOffset) => {
var now = new Date();
// convert to msec and add local time zone offset and get UTC time in msec
var utc = now.getTime() + (now.getTimezoneOffset() * 60000);
// create new Date object for different city using supplied offset
var newTime = new Date(utc + (3600000 * cityOffset));
return newTime.toLocaleString();
}

Related

How to manipulate timezone in a date object generated in nodejs [duplicate]

I have date time in a particular timezone as a string and I want to convert this to the local time. But, I don't know how to set the timezone in the Date object.
For example, I have Feb 28 2013 7:00 PM ET, then I can
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
As far as I know, I can either set the UTC time or local time. But, how do I set time in another timezone?
I tried to use the add/subtract the offset from UTC but I don't know how to counter daylight savings. Am not sure if I am heading the right direction.
How can I go about converting time from a different timezone to local time in javascript?

Background
JavaScript's Date object tracks time in UTC internally, but typically accepts input and produces output in the local time of the computer it's running on. It has very few facilities for working with time in other time zones.
The internal representation of a Date object is a single number, representing the number of milliseconds that have elapsed since 1970-01-01 00:00:00 UTC, without regard to leap seconds.
There is no time zone or string format stored in the Date object itself.
When various functions of the Date object are used, the computer's local time zone is applied to the internal representation. If the function produces a string, then the computer's locale information may be taken into consideration to determine how to produce that string. The details vary per function, and some are implementation-specific.
The only operations the Date object can do with non-local time zones are:
It can parse a string containing a numeric UTC offset from any time zone. It uses this to adjust the value being parsed, and stores the UTC equivalent. The original local time and offset are not retained in the resulting Date object. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toISOString() //=> "2020-04-12T16:00:00.000Z"
d.valueOf() //=> 1586707200000 (this is what is actually stored in the object)
In environments that have implemented the ECMASCript Internationalization API (aka "Intl"), a Date object can produce a locale-specific string adjusted to a given time zone identifier. This is accomplished via the timeZone option to toLocaleString and its variations. Most implementations will support IANA time zone identifiers, such as 'America/New_York'. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toLocaleString('en-US', { timeZone: 'America/New_York' })
//=> "4/12/2020, 12:00:00 PM"
// (midnight in China on Apring 13th is noon in New York on April 12th)
Most modern environments support the full set of IANA time zone identifiers (see the compatibility table here). However, keep in mind that the only identifier required to be supported by Intl is 'UTC', thus you should check carefully if you need to support older browsers or atypical environments (for example, lightweight IoT devices).
Libraries
There are several libraries that can be used to work with time zones. Though they still cannot make the Date object behave any differently, they typically implement the standard IANA timezone database and provide functions for using it in JavaScript. Modern libraries use the time zone data supplied by the Intl API, but older libraries typically have overhead, especially if you are running in a web browser, as the database can get a bit large. Some of these libraries also allow you to selectively reduce the data set, either by which time zones are supported and/or by the range of dates you can work with.
Here are the libraries to consider:
Intl-based Libraries
New development should choose from one of these implementations, which rely on the Intl API for their time zone data:
Luxon (successor of Moment.js)
date-fns-tz (extension for date-fns)
Day.js (when using its Timezone plugin)
Non-Intl Libraries
These libraries are maintained, but carry the burden of packaging their own time zone data, which can be quite large.
js-joda/timezone (extension for js-joda)
moment-timezone* (extension for Moment.js)
date-fns-timezone (extension for older 1.x of date-fns)
BigEasy/TimeZone
tz.js
* While Moment and Moment-Timezone were previously recommended, the Moment team now prefers users chose Luxon for new development.
Discontinued Libraries
These libraries have been officially discontinued and should no longer be used.
WallTime-js
TimeZoneJS
Future Proposals
The TC39 Temporal Proposal aims to provide a new set of standard objects for working with dates and times in the JavaScript language itself. This will include support for a time zone aware object.
Common Errors
There are several approaches that are often tried, which are in error and should usually be avoided.
Re-Parsing
new Date(new Date().toLocaleString('en', {timeZone: 'America/New_York'}))
The above approach correctly uses the Intl API to create a string in a specific time zone, but then it incorrectly passes that string back into the Date constructor. In this case, parsing will be implementation-specific, and may fail entirely. If successful, it is likely that the resulting Date object now represents the wrong instant in time, as the computer's local time zone would be applied during parsing.
Epoch Shifting
var d = new Date();
d.setTime(d.getTime() + someOffset * 60000);
The above approach attempts to manipulate the Date object's time zone by shifting the Unix timestamp by some other time zone offset. However, since the Date object only tracks time in UTC, it actually just makes the Date object represent a different point in time.
The same approach is sometimes used directly on the constructor, and is also invalid.
Epoch Shifting is sometimes used internally in date libraries as a shortcut to avoid writing calendar arithmetic. When doing so, any access to non-UTC properties must be avoided. For example, once shifted, a call to getUTCHours would be acceptable, but a call to getHours would be invalid because it uses the local time zone.
It is called "epoch shifting", because when used correctly, the Unix Epoch (1970-01-01T00:00:00.000Z) is now no longer correlated to a timestamp of 0 but has shifted to a different timestamp by the amount of the offset.
If you're not authoring a date library, you should not be epoch shifting.
For more details about epoch shifting, watch this video clip from Greg Miller at CppCon 2015. The video is about time_t in C++, but the explanation and problems are identical. (For JavaScript folks, every time you hear Greg mention time_t, just think "Date object".)
Trying to make a "UTC Date"
var d = new Date();
var utcDate = new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds()));
In this example, both d and utcDate are identical. The work to construct utcDate was redundant, because d is already in terms of UTC. Examining the output of toISOString, getTime, or valueOf functions will show identical values for both variables.
A similar approach seen is:
var d = new Date();
var utcDate = new Date(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds());
This is approach passes UTC values into the Date constructor where local time values are expected. The resulting Date object now represents a completely different point in time. It is essentially the same result as epoch shifting described earlier, and thus should be avoided.
The correct way to get a UTC-based Date object is simply new Date(). If you need a string representation that is in UTC, then use new Date().toISOString().

As Matt Johnson said
If you can limit your usage to modern web browsers, you can now do the
following without any special libraries:
new Date().toLocaleString("en-US", {timeZone: "America/New_York"})
This isn't a comprehensive solution, but it works for many scenarios
that require only output conversion (from UTC or local time to a
specific time zone, but not the other direction).
So although the browser can not read IANA timezones when creating a date, or has any methods to change the timezones on an existing Date object, there seems to be a hack around it:
function changeTimezone(date, ianatz) {
// suppose the date is 12:00 UTC
var invdate = new Date(date.toLocaleString('en-US', {
timeZone: ianatz
}));
// then invdate will be 07:00 in Toronto
// and the diff is 5 hours
var diff = date.getTime() - invdate.getTime();
// so 12:00 in Toronto is 17:00 UTC
return new Date(date.getTime() - diff); // needs to substract
}
// E.g.
var here = new Date();
var there = changeTimezone(here, "America/Toronto");
console.log(`Here: ${here.toString()}\nToronto: ${there.toString()}`);

This should solve your problem, please feel free to offer fixes. This method will account also for daylight saving time for the given date.
dateWithTimeZone = (timeZone, year, month, day, hour, minute, second) => {
let date = new Date(Date.UTC(year, month, day, hour, minute, second));
let utcDate = new Date(date.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(date.toLocaleString('en-US', { timeZone: timeZone }));
let offset = utcDate.getTime() - tzDate.getTime();
date.setTime( date.getTime() + offset );
return date;
};
How to use with timezone and local time:
dateWithTimeZone("America/Los_Angeles",2019,8,8,0,0,0)

You can specify a time zone offset on new Date(), for example:
new Date('Feb 28 2013 19:00:00 EST')
or
new Date('Feb 28 2013 19:00:00 GMT-0500')
Since Date store UTC time ( i.e. getTime returns in UTC ), javascript will them convert the time into UTC, and when you call things like toString javascript will convert the UTC time into browser's local timezone and return the string in local timezone, i.e. If I'm using UTC+8:
> new Date('Feb 28 2013 19:00:00 GMT-0500').toString()
< "Fri Mar 01 2013 08:00:00 GMT+0800 (CST)"
Also you can use normal getHours/Minute/Second method:
> new Date('Feb 28 2013 19:00:00 GMT-0500').getHours()
< 8
( This 8 means after the time is converted into my local time - UTC+8, the hours number is 8. )

I found the most supported way to do this, without worrying about a third party library, was by using getTimezoneOffset to calculate the appropriate timestamp, or update the time then use the normal methods to get the necessary date and time.
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
// ET timezone offset in hours.
var timezone = -5;
// Timezone offset in minutes + the desired offset in minutes, converted to ms.
// This offset should be the same for ALL date calculations, so you should only need to calculate it once.
var offset = (mydate.getTimezoneOffset() + (timezone * 60)) * 60 * 1000;
// Use the timestamp and offset as necessary to calculate min/sec etc, i.e. for countdowns.
var timestamp = mydate.getTime() + offset,
seconds = Math.floor(timestamp / 1000) % 60,
minutes = Math.floor(timestamp / 1000 / 60) % 60,
hours = Math.floor(timestamp / 1000 / 60 / 60);
// Or update the timestamp to reflect the timezone offset.
mydate.setTime(mydate.getTime() + offset);
// Then Output dates and times using the normal methods.
var date = mydate.getDate(),
hour = mydate.getHours();
EDIT
I was previously using UTC methods when performing the date transformations, which was incorrect. With adding the offset to the time, using the local get functions will return the desired results.

For Ionic users, I had hell with this because .toISOString() has to be used with the html template.
This will grab the current date, but of course can be added to previous answers for a selected date.
I got it fixed using this:
date = new Date();
public currentDate: any = new Date(this.date.getTime() - this.date.getTimezoneOffset()*60000).toISOString();
The *60000 is indicating the UTC -6 which is CST so whatever TimeZone is needed, the number and difference can be changed.

I ran into a similar problem with unit tests (specifically in jest when the unit tests run locally to create the snapshots and then the CI server runs in (potentially) a different timezone causing the snapshot comparison to fail). I mocked our Date and some of the supporting methods like so:
describe('...', () => {
let originalDate;
beforeEach(() => {
originalDate = Date;
Date = jest.fn(
(d) => {
let newD;
if (d) {
newD = (new originalDate(d));
} else {
newD = (new originalDate('2017-05-29T10:00:00z'));
}
newD.toLocaleString = () => {
return (new originalDate(newD.valueOf())).toLocaleString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleDateString = () => {
return (new originalDate(newD.valueOf())).toLocaleDateString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleTimeString = () => {
return (new originalDate(newD.valueOf())).toLocaleTimeString("en-US", {timeZone: "America/New_York"});
};
return newD;
}
);
Date.now = () => { return (Date()); };
});
afterEach(() => {
Date = originalDate;
});
});

I had the same problem but we can use the time zone we want
we use .toLocaleDateString()
eg:
var day=new Date();
const options= {day:'numeric', month:'long', year:"numeric", timeZone:"Asia/Kolkata"};
const today=day.toLocaleDateString("en-IN", options);
console.log(today);

I ran into this issue running a GCP Cloud Function. Of course it works on a local machine, but running in the cloud makes the OS default (local) for new Date() irrelevant. In my case, an api call from the cloud required Eastern Standard Time, in ISO format (without the "Z") with offset as "-0500" or "-0400" depending on DST, for example:
2021-12-01T00:00:00.000-0500
Again, this is not a browser formatting issue, so I am forced into this format for the api call to work correctly.
Using #chickens code as a start, this is what worked:
var date = new Date();
var now_utc = Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(),
date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
var dt = new Date(now_utc);
let utcDate = new Date(dt.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(dt.toLocaleString('en-US', { timeZone: "America/New_York" }));
let offset1 = utcDate.getTime() - tzDate.getTime();
let offset2 = offset1/60000;
let o1 = Math.abs(offset2);
console.log(offset2)
var offsetValue1 = (offset2 < 0 ? "+" : "-") + ("00" + Math.floor(o1 / 60)).slice(-2) + ("00" + (o1 % 60)).slice(-2);
console.log(offsetValue1)
dt.setTime(dt.getTime() - offset1);
console.log(dt.toISOString());
console.log(dt.toISOString().slice(0,-1)+offsetValue1);

Try using ctoc from npm.
https://www.npmjs.com/package/ctoc_timezone
It has got simple functionality to change timezones (most timezones around 400) and all custom formats u want it to display.

Building on the answers above, I am using this native one liner to convert the long timezone string to the three letter string:
var longTz = 'America/Los_Angeles';
var shortTz = new Date().
toLocaleString("en", {timeZoneName: "short", timeZone: longTz}).
split(' ').
pop();
This will give PDT or PST depending on the date provided. In my particular use case, developing on Salesforce (Aura/Lightning), we are able to get the user timezone in the long format from the backend.

Thanks to #commonpike answer, I wrote a function which takes an ISO String date such as 2020-10-10T08:00:00.000 as input and send an object which contains 2 main properties.
The first one is fromUtc is a Date corresponding to the timeZone entered as parameter.
The second one is toUtc which lets you to format a Date stemming from fromUtc.
const timeZoneTransformer = (stringDate, timeZone = "Europe/Paris") => {
const now = new Date();
const serverDate = new Date(stringDate);
const utcDate = new Date(
Date.UTC(
serverDate.getFullYear(),
serverDate.getMonth(),
serverDate.getDate(),
serverDate.getHours(),
serverDate.getMinutes(),
serverDate.getSeconds()
)
);
const invdate = new Date(
serverDate.toLocaleString("en-US", {
timeZone,
})
);
const diff = now.getTime() - invdate.getTime();
const adjustedDate = new Date(now.getTime() - diff);
return {
toUtc: utcDate,
fromUtc: adjustedDate,
};
};
const fromUtc = timeZoneTransformer("2020-10-10T08:00:00.000").fromUtc;
console.log(fromUtc);
const toUtc = timeZoneTransformer(fromUtc).toUtc;
console.log(toUtc);

Try: date-from-timezone, it resolves expected date with help of natively available Intl.DateTimeFormat.
I used that method in one of my projects for few years already, but it's now I decided to publish it as small OS project :)

Try something like this,
public static getTimezoneOffset(timeZone: string, date = new Date()): number {
const localDate = date.toLocaleString('fr', { timeZone, timeZoneName: 'long' });
const tz = localDate.split(' ');
const TZ = localDate.replace(tz[0], '').replace(tz[1], '').replace(' ', '');
const dateString = date.toString();
const offset = (Date.parse(`${dateString} UTC`) - Date.parse(`${dateString}${TZ}`)) / (3600 * 1000);
return offset;
}

I'm not sure why all these answers are so complicated. Just use YYYY-MM-DD ZZZ when creating a date-only date in the local / desired time zone.
Create a local date:
var myDate = new Date('2022-11-29 CST')
The date will be stored in storage as UTC, great.
Get the date out of storage and display it as local:
myDate.toLocaleDateString()
11/29/2022

I know its 3 years too late, but maybe it can help someone else because I haven't found anything like that except for the moment-timezone library, which is not exactly the same as what he's asking for here.
I've done something similar for german timezone,
this is a little complex because of daylight saving time and leap years where you have 366 days.
it might need a little work with the "isDaylightSavingTimeInGermany" function while different timezones change on different times the daylight saving time.
anyway, check out this page:
https://github.com/zerkotin/german-timezone-converter/wiki
the main methods are:
convertLocalDateToGermanTimezone
convertGermanDateToLocalTimezone
I've put an effort into documenting it, so it won't be so confusing.

There are several working answers here, but somehow a lot of them seemed to get you to the string, but not back to a date object you started with, so here's my simple non-function take on how to change timezone on JS date:
var TZ='Australia/Brisbane'; //Target timezone from server
var date = new Date(); //Init this to a time if you don't want current time
date=new Date(Date.parse(date.toLocaleString("en-US", {timeZone: TZ})));
//Just a clarification on what happens
// 1) First new Date() gives you a Date object at current time in the clients browser local timezone
// 2) .toLocaleString takes that time, and returns a string if time in the target timezone
// 3) Date.parse converts that new string to a Unix epoch number
// 4) new Date() converts the Unix epoch into a Date object in the new TimeZone.
// Now I can use my usual getHours and other Date functions as required.
Hope that helps others (if you get to this bottom answer!)

Simple with Node.JS support
Pass in the amount of hours your timezone is offset from UTC
function initDateInTimezone(offsetHours) {
const timezoneOffsetInMS = offsetHours * 60 * 60000;
let d = new Date().getTimezoneOffset() * 60000 + timezoneOffsetInMS;
const date = new Date(new Date().getTime() - d);
return date
}

//For Mumbai time difference is 5.5 hrs so
city_time_diff=5.5; //change according to your city
let time_now = Date.now();
time_now = time_now + (3600000 * city_time_diff); //Add our city time (in msec);
let new_date = new Date(time_now);
console.log("My city time is: ", new_date);

Was facing the same issue, used this one
Console.log(Date.parse("Jun 13, 2018 10:50:39 GMT+1"));
It will return milliseconds to which u can check have +100 timzone intialize British time
Hope it helps!!

How to set date in javascript with a different timezone than the system timezone? [duplicate]

I have date time in a particular timezone as a string and I want to convert this to the local time. But, I don't know how to set the timezone in the Date object.
For example, I have Feb 28 2013 7:00 PM ET, then I can
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
As far as I know, I can either set the UTC time or local time. But, how do I set time in another timezone?
I tried to use the add/subtract the offset from UTC but I don't know how to counter daylight savings. Am not sure if I am heading the right direction.
How can I go about converting time from a different timezone to local time in javascript?

Background
JavaScript's Date object tracks time in UTC internally, but typically accepts input and produces output in the local time of the computer it's running on. It has very few facilities for working with time in other time zones.
The internal representation of a Date object is a single number, representing the number of milliseconds that have elapsed since 1970-01-01 00:00:00 UTC, without regard to leap seconds.
There is no time zone or string format stored in the Date object itself.
When various functions of the Date object are used, the computer's local time zone is applied to the internal representation. If the function produces a string, then the computer's locale information may be taken into consideration to determine how to produce that string. The details vary per function, and some are implementation-specific.
The only operations the Date object can do with non-local time zones are:
It can parse a string containing a numeric UTC offset from any time zone. It uses this to adjust the value being parsed, and stores the UTC equivalent. The original local time and offset are not retained in the resulting Date object. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toISOString() //=> "2020-04-12T16:00:00.000Z"
d.valueOf() //=> 1586707200000 (this is what is actually stored in the object)
In environments that have implemented the ECMASCript Internationalization API (aka "Intl"), a Date object can produce a locale-specific string adjusted to a given time zone identifier. This is accomplished via the timeZone option to toLocaleString and its variations. Most implementations will support IANA time zone identifiers, such as 'America/New_York'. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toLocaleString('en-US', { timeZone: 'America/New_York' })
//=> "4/12/2020, 12:00:00 PM"
// (midnight in China on Apring 13th is noon in New York on April 12th)
Most modern environments support the full set of IANA time zone identifiers (see the compatibility table here). However, keep in mind that the only identifier required to be supported by Intl is 'UTC', thus you should check carefully if you need to support older browsers or atypical environments (for example, lightweight IoT devices).
Libraries
There are several libraries that can be used to work with time zones. Though they still cannot make the Date object behave any differently, they typically implement the standard IANA timezone database and provide functions for using it in JavaScript. Modern libraries use the time zone data supplied by the Intl API, but older libraries typically have overhead, especially if you are running in a web browser, as the database can get a bit large. Some of these libraries also allow you to selectively reduce the data set, either by which time zones are supported and/or by the range of dates you can work with.
Here are the libraries to consider:
Intl-based Libraries
New development should choose from one of these implementations, which rely on the Intl API for their time zone data:
Luxon (successor of Moment.js)
date-fns-tz (extension for date-fns)
Day.js (when using its Timezone plugin)
Non-Intl Libraries
These libraries are maintained, but carry the burden of packaging their own time zone data, which can be quite large.
js-joda/timezone (extension for js-joda)
moment-timezone* (extension for Moment.js)
date-fns-timezone (extension for older 1.x of date-fns)
BigEasy/TimeZone
tz.js
* While Moment and Moment-Timezone were previously recommended, the Moment team now prefers users chose Luxon for new development.
Discontinued Libraries
These libraries have been officially discontinued and should no longer be used.
WallTime-js
TimeZoneJS
Future Proposals
The TC39 Temporal Proposal aims to provide a new set of standard objects for working with dates and times in the JavaScript language itself. This will include support for a time zone aware object.
Common Errors
There are several approaches that are often tried, which are in error and should usually be avoided.
Re-Parsing
new Date(new Date().toLocaleString('en', {timeZone: 'America/New_York'}))
The above approach correctly uses the Intl API to create a string in a specific time zone, but then it incorrectly passes that string back into the Date constructor. In this case, parsing will be implementation-specific, and may fail entirely. If successful, it is likely that the resulting Date object now represents the wrong instant in time, as the computer's local time zone would be applied during parsing.
Epoch Shifting
var d = new Date();
d.setTime(d.getTime() + someOffset * 60000);
The above approach attempts to manipulate the Date object's time zone by shifting the Unix timestamp by some other time zone offset. However, since the Date object only tracks time in UTC, it actually just makes the Date object represent a different point in time.
The same approach is sometimes used directly on the constructor, and is also invalid.
Epoch Shifting is sometimes used internally in date libraries as a shortcut to avoid writing calendar arithmetic. When doing so, any access to non-UTC properties must be avoided. For example, once shifted, a call to getUTCHours would be acceptable, but a call to getHours would be invalid because it uses the local time zone.
It is called "epoch shifting", because when used correctly, the Unix Epoch (1970-01-01T00:00:00.000Z) is now no longer correlated to a timestamp of 0 but has shifted to a different timestamp by the amount of the offset.
If you're not authoring a date library, you should not be epoch shifting.
For more details about epoch shifting, watch this video clip from Greg Miller at CppCon 2015. The video is about time_t in C++, but the explanation and problems are identical. (For JavaScript folks, every time you hear Greg mention time_t, just think "Date object".)
Trying to make a "UTC Date"
var d = new Date();
var utcDate = new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds()));
In this example, both d and utcDate are identical. The work to construct utcDate was redundant, because d is already in terms of UTC. Examining the output of toISOString, getTime, or valueOf functions will show identical values for both variables.
A similar approach seen is:
var d = new Date();
var utcDate = new Date(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds());
This is approach passes UTC values into the Date constructor where local time values are expected. The resulting Date object now represents a completely different point in time. It is essentially the same result as epoch shifting described earlier, and thus should be avoided.
The correct way to get a UTC-based Date object is simply new Date(). If you need a string representation that is in UTC, then use new Date().toISOString().

As Matt Johnson said
If you can limit your usage to modern web browsers, you can now do the
following without any special libraries:
new Date().toLocaleString("en-US", {timeZone: "America/New_York"})
This isn't a comprehensive solution, but it works for many scenarios
that require only output conversion (from UTC or local time to a
specific time zone, but not the other direction).
So although the browser can not read IANA timezones when creating a date, or has any methods to change the timezones on an existing Date object, there seems to be a hack around it:
function changeTimezone(date, ianatz) {
// suppose the date is 12:00 UTC
var invdate = new Date(date.toLocaleString('en-US', {
timeZone: ianatz
}));
// then invdate will be 07:00 in Toronto
// and the diff is 5 hours
var diff = date.getTime() - invdate.getTime();
// so 12:00 in Toronto is 17:00 UTC
return new Date(date.getTime() - diff); // needs to substract
}
// E.g.
var here = new Date();
var there = changeTimezone(here, "America/Toronto");
console.log(`Here: ${here.toString()}\nToronto: ${there.toString()}`);

This should solve your problem, please feel free to offer fixes. This method will account also for daylight saving time for the given date.
dateWithTimeZone = (timeZone, year, month, day, hour, minute, second) => {
let date = new Date(Date.UTC(year, month, day, hour, minute, second));
let utcDate = new Date(date.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(date.toLocaleString('en-US', { timeZone: timeZone }));
let offset = utcDate.getTime() - tzDate.getTime();
date.setTime( date.getTime() + offset );
return date;
};
How to use with timezone and local time:
dateWithTimeZone("America/Los_Angeles",2019,8,8,0,0,0)

You can specify a time zone offset on new Date(), for example:
new Date('Feb 28 2013 19:00:00 EST')
or
new Date('Feb 28 2013 19:00:00 GMT-0500')
Since Date store UTC time ( i.e. getTime returns in UTC ), javascript will them convert the time into UTC, and when you call things like toString javascript will convert the UTC time into browser's local timezone and return the string in local timezone, i.e. If I'm using UTC+8:
> new Date('Feb 28 2013 19:00:00 GMT-0500').toString()
< "Fri Mar 01 2013 08:00:00 GMT+0800 (CST)"
Also you can use normal getHours/Minute/Second method:
> new Date('Feb 28 2013 19:00:00 GMT-0500').getHours()
< 8
( This 8 means after the time is converted into my local time - UTC+8, the hours number is 8. )

I found the most supported way to do this, without worrying about a third party library, was by using getTimezoneOffset to calculate the appropriate timestamp, or update the time then use the normal methods to get the necessary date and time.
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
// ET timezone offset in hours.
var timezone = -5;
// Timezone offset in minutes + the desired offset in minutes, converted to ms.
// This offset should be the same for ALL date calculations, so you should only need to calculate it once.
var offset = (mydate.getTimezoneOffset() + (timezone * 60)) * 60 * 1000;
// Use the timestamp and offset as necessary to calculate min/sec etc, i.e. for countdowns.
var timestamp = mydate.getTime() + offset,
seconds = Math.floor(timestamp / 1000) % 60,
minutes = Math.floor(timestamp / 1000 / 60) % 60,
hours = Math.floor(timestamp / 1000 / 60 / 60);
// Or update the timestamp to reflect the timezone offset.
mydate.setTime(mydate.getTime() + offset);
// Then Output dates and times using the normal methods.
var date = mydate.getDate(),
hour = mydate.getHours();
EDIT
I was previously using UTC methods when performing the date transformations, which was incorrect. With adding the offset to the time, using the local get functions will return the desired results.

For Ionic users, I had hell with this because .toISOString() has to be used with the html template.
This will grab the current date, but of course can be added to previous answers for a selected date.
I got it fixed using this:
date = new Date();
public currentDate: any = new Date(this.date.getTime() - this.date.getTimezoneOffset()*60000).toISOString();
The *60000 is indicating the UTC -6 which is CST so whatever TimeZone is needed, the number and difference can be changed.

I ran into a similar problem with unit tests (specifically in jest when the unit tests run locally to create the snapshots and then the CI server runs in (potentially) a different timezone causing the snapshot comparison to fail). I mocked our Date and some of the supporting methods like so:
describe('...', () => {
let originalDate;
beforeEach(() => {
originalDate = Date;
Date = jest.fn(
(d) => {
let newD;
if (d) {
newD = (new originalDate(d));
} else {
newD = (new originalDate('2017-05-29T10:00:00z'));
}
newD.toLocaleString = () => {
return (new originalDate(newD.valueOf())).toLocaleString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleDateString = () => {
return (new originalDate(newD.valueOf())).toLocaleDateString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleTimeString = () => {
return (new originalDate(newD.valueOf())).toLocaleTimeString("en-US", {timeZone: "America/New_York"});
};
return newD;
}
);
Date.now = () => { return (Date()); };
});
afterEach(() => {
Date = originalDate;
});
});

I had the same problem but we can use the time zone we want
we use .toLocaleDateString()
eg:
var day=new Date();
const options= {day:'numeric', month:'long', year:"numeric", timeZone:"Asia/Kolkata"};
const today=day.toLocaleDateString("en-IN", options);
console.log(today);

I ran into this issue running a GCP Cloud Function. Of course it works on a local machine, but running in the cloud makes the OS default (local) for new Date() irrelevant. In my case, an api call from the cloud required Eastern Standard Time, in ISO format (without the "Z") with offset as "-0500" or "-0400" depending on DST, for example:
2021-12-01T00:00:00.000-0500
Again, this is not a browser formatting issue, so I am forced into this format for the api call to work correctly.
Using #chickens code as a start, this is what worked:
var date = new Date();
var now_utc = Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(),
date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
var dt = new Date(now_utc);
let utcDate = new Date(dt.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(dt.toLocaleString('en-US', { timeZone: "America/New_York" }));
let offset1 = utcDate.getTime() - tzDate.getTime();
let offset2 = offset1/60000;
let o1 = Math.abs(offset2);
console.log(offset2)
var offsetValue1 = (offset2 < 0 ? "+" : "-") + ("00" + Math.floor(o1 / 60)).slice(-2) + ("00" + (o1 % 60)).slice(-2);
console.log(offsetValue1)
dt.setTime(dt.getTime() - offset1);
console.log(dt.toISOString());
console.log(dt.toISOString().slice(0,-1)+offsetValue1);

Try using ctoc from npm.
https://www.npmjs.com/package/ctoc_timezone
It has got simple functionality to change timezones (most timezones around 400) and all custom formats u want it to display.

Building on the answers above, I am using this native one liner to convert the long timezone string to the three letter string:
var longTz = 'America/Los_Angeles';
var shortTz = new Date().
toLocaleString("en", {timeZoneName: "short", timeZone: longTz}).
split(' ').
pop();
This will give PDT or PST depending on the date provided. In my particular use case, developing on Salesforce (Aura/Lightning), we are able to get the user timezone in the long format from the backend.

Thanks to #commonpike answer, I wrote a function which takes an ISO String date such as 2020-10-10T08:00:00.000 as input and send an object which contains 2 main properties.
The first one is fromUtc is a Date corresponding to the timeZone entered as parameter.
The second one is toUtc which lets you to format a Date stemming from fromUtc.
const timeZoneTransformer = (stringDate, timeZone = "Europe/Paris") => {
const now = new Date();
const serverDate = new Date(stringDate);
const utcDate = new Date(
Date.UTC(
serverDate.getFullYear(),
serverDate.getMonth(),
serverDate.getDate(),
serverDate.getHours(),
serverDate.getMinutes(),
serverDate.getSeconds()
)
);
const invdate = new Date(
serverDate.toLocaleString("en-US", {
timeZone,
})
);
const diff = now.getTime() - invdate.getTime();
const adjustedDate = new Date(now.getTime() - diff);
return {
toUtc: utcDate,
fromUtc: adjustedDate,
};
};
const fromUtc = timeZoneTransformer("2020-10-10T08:00:00.000").fromUtc;
console.log(fromUtc);
const toUtc = timeZoneTransformer(fromUtc).toUtc;
console.log(toUtc);

Try: date-from-timezone, it resolves expected date with help of natively available Intl.DateTimeFormat.
I used that method in one of my projects for few years already, but it's now I decided to publish it as small OS project :)

Try something like this,
public static getTimezoneOffset(timeZone: string, date = new Date()): number {
const localDate = date.toLocaleString('fr', { timeZone, timeZoneName: 'long' });
const tz = localDate.split(' ');
const TZ = localDate.replace(tz[0], '').replace(tz[1], '').replace(' ', '');
const dateString = date.toString();
const offset = (Date.parse(`${dateString} UTC`) - Date.parse(`${dateString}${TZ}`)) / (3600 * 1000);
return offset;
}

I'm not sure why all these answers are so complicated. Just use YYYY-MM-DD ZZZ when creating a date-only date in the local / desired time zone.
Create a local date:
var myDate = new Date('2022-11-29 CST')
The date will be stored in storage as UTC, great.
Get the date out of storage and display it as local:
myDate.toLocaleDateString()
11/29/2022

I know its 3 years too late, but maybe it can help someone else because I haven't found anything like that except for the moment-timezone library, which is not exactly the same as what he's asking for here.
I've done something similar for german timezone,
this is a little complex because of daylight saving time and leap years where you have 366 days.
it might need a little work with the "isDaylightSavingTimeInGermany" function while different timezones change on different times the daylight saving time.
anyway, check out this page:
https://github.com/zerkotin/german-timezone-converter/wiki
the main methods are:
convertLocalDateToGermanTimezone
convertGermanDateToLocalTimezone
I've put an effort into documenting it, so it won't be so confusing.

There are several working answers here, but somehow a lot of them seemed to get you to the string, but not back to a date object you started with, so here's my simple non-function take on how to change timezone on JS date:
var TZ='Australia/Brisbane'; //Target timezone from server
var date = new Date(); //Init this to a time if you don't want current time
date=new Date(Date.parse(date.toLocaleString("en-US", {timeZone: TZ})));
//Just a clarification on what happens
// 1) First new Date() gives you a Date object at current time in the clients browser local timezone
// 2) .toLocaleString takes that time, and returns a string if time in the target timezone
// 3) Date.parse converts that new string to a Unix epoch number
// 4) new Date() converts the Unix epoch into a Date object in the new TimeZone.
// Now I can use my usual getHours and other Date functions as required.
Hope that helps others (if you get to this bottom answer!)

Simple with Node.JS support
Pass in the amount of hours your timezone is offset from UTC
function initDateInTimezone(offsetHours) {
const timezoneOffsetInMS = offsetHours * 60 * 60000;
let d = new Date().getTimezoneOffset() * 60000 + timezoneOffsetInMS;
const date = new Date(new Date().getTime() - d);
return date
}

//For Mumbai time difference is 5.5 hrs so
city_time_diff=5.5; //change according to your city
let time_now = Date.now();
time_now = time_now + (3600000 * city_time_diff); //Add our city time (in msec);
let new_date = new Date(time_now);
console.log("My city time is: ", new_date);

Was facing the same issue, used this one
Console.log(Date.parse("Jun 13, 2018 10:50:39 GMT+1"));
It will return milliseconds to which u can check have +100 timzone intialize British time
Hope it helps!!

How to change timezone without changing date value

My scenario is this:
I have a datepicker that accepts input from the user and it assumes the date/time picked is local time. I can't seem to change this behavior. The user should actually be picking the date/time in Europe/London time as they are booking a service in London at that time.
Lets say they are booking a flight from London at 5AM.
So I have this date the user picked (from New Zealand):
2019-08-01T05:00:00+12:00 (NZ time)
I need to change this to:
2019-08-01T05:00:00+01:00 (Europe/London time)
After that I am sending to server and storing as UTC.
I am using momentjs if that helps.
Edit:
Latest attempt:
I just need to figure out how to get the timezone offset from the exact time the user entered so I have daylight savings covered.
e.g. below I am getting the UK offset for the day before so may have DST issues
const moment = require('moment-timezone');
const nzd = '2019-08-01T05:00:00+12:00'; // This is the date my user entered via the datepicker
const ukTempString = moment(new Date(nzd.slice(0, -6))).tz('Europe/London').format('YYYY-MM-DDTHH:mm:ssZ'); // 2019-07-31T18:00:00+01:00
const ukOffset = ukTempString.substr(ukTempString.length - 6); // +01:00
const ukString = nzd.slice(0, -6) + ukOffset; // 2019-08-01T05:00:00+01:00
const ukDate = new Date(ukString); // I can then this to the backend
Edit:
Current solution:
No DST in UK example:
let nzd = moment('2019-10-27T05:00:00+13:00'); // This is the date my user entered via the datepicker
let nzString = nzd.format('YYYY-MM-DDTHH:mm:ssZ');
let ukd = moment().tz('Europe/London');
ukd.set(nzd.toObject());
console.log(ukd.format('YYYY-MM-DDTHH:mm:ssZ')); // 2019-10-27T05:00:00+00:00
let ukDate = new Date(ukd.format('YYYY-MM-DDTHH:mm:ssZ')); // I can then this to the backend
console.log(ukDate.toUTCString()); // Sun, 27 Oct 2019 05:00:00 GMT
Has DST in UK example (same code):
nzd = moment('2019-10-27T00:30:00+13:00'); // This is the date my user entered via the datepicker
nzString = nzd.format('YYYY-MM-DDTHH:mm:ssZ');
ukd = moment().tz('Europe/London');
ukd.set(nzd.toObject());
console.log(ukd.format('YYYY-MM-DDTHH:mm:ssZ')); // 2019-10-27T00:30:00+01:00
ukDate = new Date(ukd.format('YYYY-MM-DDTHH:mm:ssZ')); // I can then this to the backend
console.log(ukDate.toUTCString()); // Sat, 26 Oct 2019 23:30:00 GMT

Here is a simpler solution:
moment("2019-08-01T05:00:00+12:00")
.parseZone()
.tz("Europe/London", true)
.toISOString(true) // => "2019-08-01T05:00:00.000+01:00"
To explain that a bit:
We parse the string, which interprets the string as being in NZ, but translates it to a local time, which may or may not be +12, depending on where your computer is
use parseZone to undo that conversion, so that our date thinks of itself as being in +12, per the original string
Convert the time to London time using tz, but with the a second argument (called keepTime) of true, which means "instead of keeping the time the same and changing the local time, change what time it is to keep the local time the same".
Format the result in ISO, but pass a second argument (called keepOffset) telling it not to convert to UTC before display
So, that works, but perhaps it would be better to change the timepicker to London time so that the times they pick are already in the zone you want?
Edit, the equivalent Luxon code is a little more legible, if that helps explain it:
DateTime.fromISO("2019-08-01T05:00:00+12:00", { setZone: true })
.setZone("Europe/London", { keepLocalTime: true} )
.toISO()

If you are not doing any date time conversion (like in your example), and just changing the time zone offset in the end of the string, just do a string operation, like this:
var nzd = '2019-08-01T05:00:00+12:00'
var ukd = nzd.slice(0, -6) + '+01:00'
console.log(ukd) // outputs 2019-08-01T05:00:00+01:00
If you need to convert the full date and time, as you are using momentjs, you could use moment-timezone instead: https://momentjs.com/timezone/ . Then the following code do the trick:
const moment = require('moment-timezone')
var nz = moment('2019-08-01T05:00:00+12:00')
var uk = nz.tz('Europe/London').format()
console.log(uk) // outputs 2019-07-31T18:00:00+01:00
If you want to get the time zone offset string, also use moment-timezone:
let ukd = "2019-10-27T01:59:00".split('T')
let finalDate = moment.tz(ukd[0] + "T" + ukd[1], "YYYY-MM-DDTHH:mm:ss", true, "Europe/London").tz('Europe/London').format('Z');
console.log(finalDate) // last minute still in DST, outputs +01:00
ukd = "2019-10-27T02:01:00".split('T')
finalDate = moment.tz(ukd[0] + "T" + ukd[1], "YYYY-MM-DDTHH:mm:ss", true, "Europe/London").tz('Europe/London').format('Z');
console.log(finalDate) // first minute after DST, outputs +00:00
This seems hacky and not clean code, but it's due to a bug in timezone that parses as UTC date instead of timezone date.

Store date + timezone in UTC [duplicate]

I have date time in a particular timezone as a string and I want to convert this to the local time. But, I don't know how to set the timezone in the Date object.
For example, I have Feb 28 2013 7:00 PM ET, then I can
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
As far as I know, I can either set the UTC time or local time. But, how do I set time in another timezone?
I tried to use the add/subtract the offset from UTC but I don't know how to counter daylight savings. Am not sure if I am heading the right direction.
How can I go about converting time from a different timezone to local time in javascript?

Background
JavaScript's Date object tracks time in UTC internally, but typically accepts input and produces output in the local time of the computer it's running on. It has very few facilities for working with time in other time zones.
The internal representation of a Date object is a single number, representing the number of milliseconds that have elapsed since 1970-01-01 00:00:00 UTC, without regard to leap seconds.
There is no time zone or string format stored in the Date object itself.
When various functions of the Date object are used, the computer's local time zone is applied to the internal representation. If the function produces a string, then the computer's locale information may be taken into consideration to determine how to produce that string. The details vary per function, and some are implementation-specific.
The only operations the Date object can do with non-local time zones are:
It can parse a string containing a numeric UTC offset from any time zone. It uses this to adjust the value being parsed, and stores the UTC equivalent. The original local time and offset are not retained in the resulting Date object. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toISOString() //=> "2020-04-12T16:00:00.000Z"
d.valueOf() //=> 1586707200000 (this is what is actually stored in the object)
In environments that have implemented the ECMASCript Internationalization API (aka "Intl"), a Date object can produce a locale-specific string adjusted to a given time zone identifier. This is accomplished via the timeZone option to toLocaleString and its variations. Most implementations will support IANA time zone identifiers, such as 'America/New_York'. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toLocaleString('en-US', { timeZone: 'America/New_York' })
//=> "4/12/2020, 12:00:00 PM"
// (midnight in China on Apring 13th is noon in New York on April 12th)
Most modern environments support the full set of IANA time zone identifiers (see the compatibility table here). However, keep in mind that the only identifier required to be supported by Intl is 'UTC', thus you should check carefully if you need to support older browsers or atypical environments (for example, lightweight IoT devices).
Libraries
There are several libraries that can be used to work with time zones. Though they still cannot make the Date object behave any differently, they typically implement the standard IANA timezone database and provide functions for using it in JavaScript. Modern libraries use the time zone data supplied by the Intl API, but older libraries typically have overhead, especially if you are running in a web browser, as the database can get a bit large. Some of these libraries also allow you to selectively reduce the data set, either by which time zones are supported and/or by the range of dates you can work with.
Here are the libraries to consider:
Intl-based Libraries
New development should choose from one of these implementations, which rely on the Intl API for their time zone data:
Luxon (successor of Moment.js)
date-fns-tz (extension for date-fns)
Day.js (when using its Timezone plugin)
Non-Intl Libraries
These libraries are maintained, but carry the burden of packaging their own time zone data, which can be quite large.
js-joda/timezone (extension for js-joda)
moment-timezone* (extension for Moment.js)
date-fns-timezone (extension for older 1.x of date-fns)
BigEasy/TimeZone
tz.js
* While Moment and Moment-Timezone were previously recommended, the Moment team now prefers users chose Luxon for new development.
Discontinued Libraries
These libraries have been officially discontinued and should no longer be used.
WallTime-js
TimeZoneJS
Future Proposals
The TC39 Temporal Proposal aims to provide a new set of standard objects for working with dates and times in the JavaScript language itself. This will include support for a time zone aware object.
Common Errors
There are several approaches that are often tried, which are in error and should usually be avoided.
Re-Parsing
new Date(new Date().toLocaleString('en', {timeZone: 'America/New_York'}))
The above approach correctly uses the Intl API to create a string in a specific time zone, but then it incorrectly passes that string back into the Date constructor. In this case, parsing will be implementation-specific, and may fail entirely. If successful, it is likely that the resulting Date object now represents the wrong instant in time, as the computer's local time zone would be applied during parsing.
Epoch Shifting
var d = new Date();
d.setTime(d.getTime() + someOffset * 60000);
The above approach attempts to manipulate the Date object's time zone by shifting the Unix timestamp by some other time zone offset. However, since the Date object only tracks time in UTC, it actually just makes the Date object represent a different point in time.
The same approach is sometimes used directly on the constructor, and is also invalid.
Epoch Shifting is sometimes used internally in date libraries as a shortcut to avoid writing calendar arithmetic. When doing so, any access to non-UTC properties must be avoided. For example, once shifted, a call to getUTCHours would be acceptable, but a call to getHours would be invalid because it uses the local time zone.
It is called "epoch shifting", because when used correctly, the Unix Epoch (1970-01-01T00:00:00.000Z) is now no longer correlated to a timestamp of 0 but has shifted to a different timestamp by the amount of the offset.
If you're not authoring a date library, you should not be epoch shifting.
For more details about epoch shifting, watch this video clip from Greg Miller at CppCon 2015. The video is about time_t in C++, but the explanation and problems are identical. (For JavaScript folks, every time you hear Greg mention time_t, just think "Date object".)
Trying to make a "UTC Date"
var d = new Date();
var utcDate = new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds()));
In this example, both d and utcDate are identical. The work to construct utcDate was redundant, because d is already in terms of UTC. Examining the output of toISOString, getTime, or valueOf functions will show identical values for both variables.
A similar approach seen is:
var d = new Date();
var utcDate = new Date(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds());
This is approach passes UTC values into the Date constructor where local time values are expected. The resulting Date object now represents a completely different point in time. It is essentially the same result as epoch shifting described earlier, and thus should be avoided.
The correct way to get a UTC-based Date object is simply new Date(). If you need a string representation that is in UTC, then use new Date().toISOString().

As Matt Johnson said
If you can limit your usage to modern web browsers, you can now do the
following without any special libraries:
new Date().toLocaleString("en-US", {timeZone: "America/New_York"})
This isn't a comprehensive solution, but it works for many scenarios
that require only output conversion (from UTC or local time to a
specific time zone, but not the other direction).
So although the browser can not read IANA timezones when creating a date, or has any methods to change the timezones on an existing Date object, there seems to be a hack around it:
function changeTimezone(date, ianatz) {
// suppose the date is 12:00 UTC
var invdate = new Date(date.toLocaleString('en-US', {
timeZone: ianatz
}));
// then invdate will be 07:00 in Toronto
// and the diff is 5 hours
var diff = date.getTime() - invdate.getTime();
// so 12:00 in Toronto is 17:00 UTC
return new Date(date.getTime() - diff); // needs to substract
}
// E.g.
var here = new Date();
var there = changeTimezone(here, "America/Toronto");
console.log(`Here: ${here.toString()}\nToronto: ${there.toString()}`);

This should solve your problem, please feel free to offer fixes. This method will account also for daylight saving time for the given date.
dateWithTimeZone = (timeZone, year, month, day, hour, minute, second) => {
let date = new Date(Date.UTC(year, month, day, hour, minute, second));
let utcDate = new Date(date.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(date.toLocaleString('en-US', { timeZone: timeZone }));
let offset = utcDate.getTime() - tzDate.getTime();
date.setTime( date.getTime() + offset );
return date;
};
How to use with timezone and local time:
dateWithTimeZone("America/Los_Angeles",2019,8,8,0,0,0)

You can specify a time zone offset on new Date(), for example:
new Date('Feb 28 2013 19:00:00 EST')
or
new Date('Feb 28 2013 19:00:00 GMT-0500')
Since Date store UTC time ( i.e. getTime returns in UTC ), javascript will them convert the time into UTC, and when you call things like toString javascript will convert the UTC time into browser's local timezone and return the string in local timezone, i.e. If I'm using UTC+8:
> new Date('Feb 28 2013 19:00:00 GMT-0500').toString()
< "Fri Mar 01 2013 08:00:00 GMT+0800 (CST)"
Also you can use normal getHours/Minute/Second method:
> new Date('Feb 28 2013 19:00:00 GMT-0500').getHours()
< 8
( This 8 means after the time is converted into my local time - UTC+8, the hours number is 8. )

I found the most supported way to do this, without worrying about a third party library, was by using getTimezoneOffset to calculate the appropriate timestamp, or update the time then use the normal methods to get the necessary date and time.
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
// ET timezone offset in hours.
var timezone = -5;
// Timezone offset in minutes + the desired offset in minutes, converted to ms.
// This offset should be the same for ALL date calculations, so you should only need to calculate it once.
var offset = (mydate.getTimezoneOffset() + (timezone * 60)) * 60 * 1000;
// Use the timestamp and offset as necessary to calculate min/sec etc, i.e. for countdowns.
var timestamp = mydate.getTime() + offset,
seconds = Math.floor(timestamp / 1000) % 60,
minutes = Math.floor(timestamp / 1000 / 60) % 60,
hours = Math.floor(timestamp / 1000 / 60 / 60);
// Or update the timestamp to reflect the timezone offset.
mydate.setTime(mydate.getTime() + offset);
// Then Output dates and times using the normal methods.
var date = mydate.getDate(),
hour = mydate.getHours();
EDIT
I was previously using UTC methods when performing the date transformations, which was incorrect. With adding the offset to the time, using the local get functions will return the desired results.

For Ionic users, I had hell with this because .toISOString() has to be used with the html template.
This will grab the current date, but of course can be added to previous answers for a selected date.
I got it fixed using this:
date = new Date();
public currentDate: any = new Date(this.date.getTime() - this.date.getTimezoneOffset()*60000).toISOString();
The *60000 is indicating the UTC -6 which is CST so whatever TimeZone is needed, the number and difference can be changed.

I ran into this issue running a GCP Cloud Function. Of course it works on a local machine, but running in the cloud makes the OS default (local) for new Date() irrelevant. In my case, an api call from the cloud required Eastern Standard Time, in ISO format (without the "Z") with offset as "-0500" or "-0400" depending on DST, for example:
2021-12-01T00:00:00.000-0500
Again, this is not a browser formatting issue, so I am forced into this format for the api call to work correctly.
Using #chickens code as a start, this is what worked:
var date = new Date();
var now_utc = Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(),
date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
var dt = new Date(now_utc);
let utcDate = new Date(dt.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(dt.toLocaleString('en-US', { timeZone: "America/New_York" }));
let offset1 = utcDate.getTime() - tzDate.getTime();
let offset2 = offset1/60000;
let o1 = Math.abs(offset2);
console.log(offset2)
var offsetValue1 = (offset2 < 0 ? "+" : "-") + ("00" + Math.floor(o1 / 60)).slice(-2) + ("00" + (o1 % 60)).slice(-2);
console.log(offsetValue1)
dt.setTime(dt.getTime() - offset1);
console.log(dt.toISOString());
console.log(dt.toISOString().slice(0,-1)+offsetValue1);

I ran into a similar problem with unit tests (specifically in jest when the unit tests run locally to create the snapshots and then the CI server runs in (potentially) a different timezone causing the snapshot comparison to fail). I mocked our Date and some of the supporting methods like so:
describe('...', () => {
let originalDate;
beforeEach(() => {
originalDate = Date;
Date = jest.fn(
(d) => {
let newD;
if (d) {
newD = (new originalDate(d));
} else {
newD = (new originalDate('2017-05-29T10:00:00z'));
}
newD.toLocaleString = () => {
return (new originalDate(newD.valueOf())).toLocaleString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleDateString = () => {
return (new originalDate(newD.valueOf())).toLocaleDateString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleTimeString = () => {
return (new originalDate(newD.valueOf())).toLocaleTimeString("en-US", {timeZone: "America/New_York"});
};
return newD;
}
);
Date.now = () => { return (Date()); };
});
afterEach(() => {
Date = originalDate;
});
});

I had the same problem but we can use the time zone we want
we use .toLocaleDateString()
eg:
var day=new Date();
const options= {day:'numeric', month:'long', year:"numeric", timeZone:"Asia/Kolkata"};
const today=day.toLocaleDateString("en-IN", options);
console.log(today);

Try using ctoc from npm.
https://www.npmjs.com/package/ctoc_timezone
It has got simple functionality to change timezones (most timezones around 400) and all custom formats u want it to display.

Building on the answers above, I am using this native one liner to convert the long timezone string to the three letter string:
var longTz = 'America/Los_Angeles';
var shortTz = new Date().
toLocaleString("en", {timeZoneName: "short", timeZone: longTz}).
split(' ').
pop();
This will give PDT or PST depending on the date provided. In my particular use case, developing on Salesforce (Aura/Lightning), we are able to get the user timezone in the long format from the backend.

Thanks to #commonpike answer, I wrote a function which takes an ISO String date such as 2020-10-10T08:00:00.000 as input and send an object which contains 2 main properties.
The first one is fromUtc is a Date corresponding to the timeZone entered as parameter.
The second one is toUtc which lets you to format a Date stemming from fromUtc.
const timeZoneTransformer = (stringDate, timeZone = "Europe/Paris") => {
const now = new Date();
const serverDate = new Date(stringDate);
const utcDate = new Date(
Date.UTC(
serverDate.getFullYear(),
serverDate.getMonth(),
serverDate.getDate(),
serverDate.getHours(),
serverDate.getMinutes(),
serverDate.getSeconds()
)
);
const invdate = new Date(
serverDate.toLocaleString("en-US", {
timeZone,
})
);
const diff = now.getTime() - invdate.getTime();
const adjustedDate = new Date(now.getTime() - diff);
return {
toUtc: utcDate,
fromUtc: adjustedDate,
};
};
const fromUtc = timeZoneTransformer("2020-10-10T08:00:00.000").fromUtc;
console.log(fromUtc);
const toUtc = timeZoneTransformer(fromUtc).toUtc;
console.log(toUtc);

Try: date-from-timezone, it resolves expected date with help of natively available Intl.DateTimeFormat.
I used that method in one of my projects for few years already, but it's now I decided to publish it as small OS project :)

Try something like this,
public static getTimezoneOffset(timeZone: string, date = new Date()): number {
const localDate = date.toLocaleString('fr', { timeZone, timeZoneName: 'long' });
const tz = localDate.split(' ');
const TZ = localDate.replace(tz[0], '').replace(tz[1], '').replace(' ', '');
const dateString = date.toString();
const offset = (Date.parse(`${dateString} UTC`) - Date.parse(`${dateString}${TZ}`)) / (3600 * 1000);
return offset;
}

I'm not sure why all these answers are so complicated. Just use YYYY-MM-DD ZZZ when creating a date-only date in the local / desired time zone.
Create a local date:
var myDate = new Date('2022-11-29 CST')
The date will be stored in storage as UTC, great.
Get the date out of storage and display it as local:
myDate.toLocaleDateString()
11/29/2022

I know its 3 years too late, but maybe it can help someone else because I haven't found anything like that except for the moment-timezone library, which is not exactly the same as what he's asking for here.
I've done something similar for german timezone,
this is a little complex because of daylight saving time and leap years where you have 366 days.
it might need a little work with the "isDaylightSavingTimeInGermany" function while different timezones change on different times the daylight saving time.
anyway, check out this page:
https://github.com/zerkotin/german-timezone-converter/wiki
the main methods are:
convertLocalDateToGermanTimezone
convertGermanDateToLocalTimezone
I've put an effort into documenting it, so it won't be so confusing.

There are several working answers here, but somehow a lot of them seemed to get you to the string, but not back to a date object you started with, so here's my simple non-function take on how to change timezone on JS date:
var TZ='Australia/Brisbane'; //Target timezone from server
var date = new Date(); //Init this to a time if you don't want current time
date=new Date(Date.parse(date.toLocaleString("en-US", {timeZone: TZ})));
//Just a clarification on what happens
// 1) First new Date() gives you a Date object at current time in the clients browser local timezone
// 2) .toLocaleString takes that time, and returns a string if time in the target timezone
// 3) Date.parse converts that new string to a Unix epoch number
// 4) new Date() converts the Unix epoch into a Date object in the new TimeZone.
// Now I can use my usual getHours and other Date functions as required.
Hope that helps others (if you get to this bottom answer!)

Simple with Node.JS support
Pass in the amount of hours your timezone is offset from UTC
function initDateInTimezone(offsetHours) {
const timezoneOffsetInMS = offsetHours * 60 * 60000;
let d = new Date().getTimezoneOffset() * 60000 + timezoneOffsetInMS;
const date = new Date(new Date().getTime() - d);
return date
}

//For Mumbai time difference is 5.5 hrs so
city_time_diff=5.5; //change according to your city
let time_now = Date.now();
time_now = time_now + (3600000 * city_time_diff); //Add our city time (in msec);
let new_date = new Date(time_now);
console.log("My city time is: ", new_date);

Was facing the same issue, used this one
Console.log(Date.parse("Jun 13, 2018 10:50:39 GMT+1"));
It will return milliseconds to which u can check have +100 timzone intialize British time
Hope it helps!!

How to initialize a JavaScript Date to a particular time zone

I have date time in a particular timezone as a string and I want to convert this to the local time. But, I don't know how to set the timezone in the Date object.
For example, I have Feb 28 2013 7:00 PM ET, then I can
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
As far as I know, I can either set the UTC time or local time. But, how do I set time in another timezone?
I tried to use the add/subtract the offset from UTC but I don't know how to counter daylight savings. Am not sure if I am heading the right direction.
How can I go about converting time from a different timezone to local time in javascript?

Background
JavaScript's Date object tracks time in UTC internally, but typically accepts input and produces output in the local time of the computer it's running on. It has very few facilities for working with time in other time zones.
The internal representation of a Date object is a single number, representing the number of milliseconds that have elapsed since 1970-01-01 00:00:00 UTC, without regard to leap seconds.
There is no time zone or string format stored in the Date object itself.
When various functions of the Date object are used, the computer's local time zone is applied to the internal representation. If the function produces a string, then the computer's locale information may be taken into consideration to determine how to produce that string. The details vary per function, and some are implementation-specific.
The only operations the Date object can do with non-local time zones are:
It can parse a string containing a numeric UTC offset from any time zone. It uses this to adjust the value being parsed, and stores the UTC equivalent. The original local time and offset are not retained in the resulting Date object. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toISOString() //=> "2020-04-12T16:00:00.000Z"
d.valueOf() //=> 1586707200000 (this is what is actually stored in the object)
In environments that have implemented the ECMASCript Internationalization API (aka "Intl"), a Date object can produce a locale-specific string adjusted to a given time zone identifier. This is accomplished via the timeZone option to toLocaleString and its variations. Most implementations will support IANA time zone identifiers, such as 'America/New_York'. For example:
var d = new Date("2020-04-13T00:00:00.000+08:00");
d.toLocaleString('en-US', { timeZone: 'America/New_York' })
//=> "4/12/2020, 12:00:00 PM"
// (midnight in China on Apring 13th is noon in New York on April 12th)
Most modern environments support the full set of IANA time zone identifiers (see the compatibility table here). However, keep in mind that the only identifier required to be supported by Intl is 'UTC', thus you should check carefully if you need to support older browsers or atypical environments (for example, lightweight IoT devices).
Libraries
There are several libraries that can be used to work with time zones. Though they still cannot make the Date object behave any differently, they typically implement the standard IANA timezone database and provide functions for using it in JavaScript. Modern libraries use the time zone data supplied by the Intl API, but older libraries typically have overhead, especially if you are running in a web browser, as the database can get a bit large. Some of these libraries also allow you to selectively reduce the data set, either by which time zones are supported and/or by the range of dates you can work with.
Here are the libraries to consider:
Intl-based Libraries
New development should choose from one of these implementations, which rely on the Intl API for their time zone data:
Luxon (successor of Moment.js)
date-fns-tz (extension for date-fns)
Day.js (when using its Timezone plugin)
Non-Intl Libraries
These libraries are maintained, but carry the burden of packaging their own time zone data, which can be quite large.
js-joda/timezone (extension for js-joda)
moment-timezone* (extension for Moment.js)
date-fns-timezone (extension for older 1.x of date-fns)
BigEasy/TimeZone
tz.js
* While Moment and Moment-Timezone were previously recommended, the Moment team now prefers users chose Luxon for new development.
Discontinued Libraries
These libraries have been officially discontinued and should no longer be used.
WallTime-js
TimeZoneJS
Future Proposals
The TC39 Temporal Proposal aims to provide a new set of standard objects for working with dates and times in the JavaScript language itself. This will include support for a time zone aware object.
Common Errors
There are several approaches that are often tried, which are in error and should usually be avoided.
Re-Parsing
new Date(new Date().toLocaleString('en', {timeZone: 'America/New_York'}))
The above approach correctly uses the Intl API to create a string in a specific time zone, but then it incorrectly passes that string back into the Date constructor. In this case, parsing will be implementation-specific, and may fail entirely. If successful, it is likely that the resulting Date object now represents the wrong instant in time, as the computer's local time zone would be applied during parsing.
Epoch Shifting
var d = new Date();
d.setTime(d.getTime() + someOffset * 60000);
The above approach attempts to manipulate the Date object's time zone by shifting the Unix timestamp by some other time zone offset. However, since the Date object only tracks time in UTC, it actually just makes the Date object represent a different point in time.
The same approach is sometimes used directly on the constructor, and is also invalid.
Epoch Shifting is sometimes used internally in date libraries as a shortcut to avoid writing calendar arithmetic. When doing so, any access to non-UTC properties must be avoided. For example, once shifted, a call to getUTCHours would be acceptable, but a call to getHours would be invalid because it uses the local time zone.
It is called "epoch shifting", because when used correctly, the Unix Epoch (1970-01-01T00:00:00.000Z) is now no longer correlated to a timestamp of 0 but has shifted to a different timestamp by the amount of the offset.
If you're not authoring a date library, you should not be epoch shifting.
For more details about epoch shifting, watch this video clip from Greg Miller at CppCon 2015. The video is about time_t in C++, but the explanation and problems are identical. (For JavaScript folks, every time you hear Greg mention time_t, just think "Date object".)
Trying to make a "UTC Date"
var d = new Date();
var utcDate = new Date(Date.UTC(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds()));
In this example, both d and utcDate are identical. The work to construct utcDate was redundant, because d is already in terms of UTC. Examining the output of toISOString, getTime, or valueOf functions will show identical values for both variables.
A similar approach seen is:
var d = new Date();
var utcDate = new Date(d.getUTCFullYear(), d.getUTCMonth(), d.getUTCDate(), d.getUTCHours(), d.getUTCMinutes(), d.getUTCSeconds(), d.getUTCMilliseconds());
This is approach passes UTC values into the Date constructor where local time values are expected. The resulting Date object now represents a completely different point in time. It is essentially the same result as epoch shifting described earlier, and thus should be avoided.
The correct way to get a UTC-based Date object is simply new Date(). If you need a string representation that is in UTC, then use new Date().toISOString().

As Matt Johnson said
If you can limit your usage to modern web browsers, you can now do the
following without any special libraries:
new Date().toLocaleString("en-US", {timeZone: "America/New_York"})
This isn't a comprehensive solution, but it works for many scenarios
that require only output conversion (from UTC or local time to a
specific time zone, but not the other direction).
So although the browser can not read IANA timezones when creating a date, or has any methods to change the timezones on an existing Date object, there seems to be a hack around it:
function changeTimezone(date, ianatz) {
// suppose the date is 12:00 UTC
var invdate = new Date(date.toLocaleString('en-US', {
timeZone: ianatz
}));
// then invdate will be 07:00 in Toronto
// and the diff is 5 hours
var diff = date.getTime() - invdate.getTime();
// so 12:00 in Toronto is 17:00 UTC
return new Date(date.getTime() - diff); // needs to substract
}
// E.g.
var here = new Date();
var there = changeTimezone(here, "America/Toronto");
console.log(`Here: ${here.toString()}\nToronto: ${there.toString()}`);

This should solve your problem, please feel free to offer fixes. This method will account also for daylight saving time for the given date.
dateWithTimeZone = (timeZone, year, month, day, hour, minute, second) => {
let date = new Date(Date.UTC(year, month, day, hour, minute, second));
let utcDate = new Date(date.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(date.toLocaleString('en-US', { timeZone: timeZone }));
let offset = utcDate.getTime() - tzDate.getTime();
date.setTime( date.getTime() + offset );
return date;
};
How to use with timezone and local time:
dateWithTimeZone("America/Los_Angeles",2019,8,8,0,0,0)

You can specify a time zone offset on new Date(), for example:
new Date('Feb 28 2013 19:00:00 EST')
or
new Date('Feb 28 2013 19:00:00 GMT-0500')
Since Date store UTC time ( i.e. getTime returns in UTC ), javascript will them convert the time into UTC, and when you call things like toString javascript will convert the UTC time into browser's local timezone and return the string in local timezone, i.e. If I'm using UTC+8:
> new Date('Feb 28 2013 19:00:00 GMT-0500').toString()
< "Fri Mar 01 2013 08:00:00 GMT+0800 (CST)"
Also you can use normal getHours/Minute/Second method:
> new Date('Feb 28 2013 19:00:00 GMT-0500').getHours()
< 8
( This 8 means after the time is converted into my local time - UTC+8, the hours number is 8. )

I found the most supported way to do this, without worrying about a third party library, was by using getTimezoneOffset to calculate the appropriate timestamp, or update the time then use the normal methods to get the necessary date and time.
var mydate = new Date();
mydate.setFullYear(2013);
mydate.setMonth(02);
mydate.setDate(28);
mydate.setHours(7);
mydate.setMinutes(00);
// ET timezone offset in hours.
var timezone = -5;
// Timezone offset in minutes + the desired offset in minutes, converted to ms.
// This offset should be the same for ALL date calculations, so you should only need to calculate it once.
var offset = (mydate.getTimezoneOffset() + (timezone * 60)) * 60 * 1000;
// Use the timestamp and offset as necessary to calculate min/sec etc, i.e. for countdowns.
var timestamp = mydate.getTime() + offset,
seconds = Math.floor(timestamp / 1000) % 60,
minutes = Math.floor(timestamp / 1000 / 60) % 60,
hours = Math.floor(timestamp / 1000 / 60 / 60);
// Or update the timestamp to reflect the timezone offset.
mydate.setTime(mydate.getTime() + offset);
// Then Output dates and times using the normal methods.
var date = mydate.getDate(),
hour = mydate.getHours();
EDIT
I was previously using UTC methods when performing the date transformations, which was incorrect. With adding the offset to the time, using the local get functions will return the desired results.

For Ionic users, I had hell with this because .toISOString() has to be used with the html template.
This will grab the current date, but of course can be added to previous answers for a selected date.
I got it fixed using this:
date = new Date();
public currentDate: any = new Date(this.date.getTime() - this.date.getTimezoneOffset()*60000).toISOString();
The *60000 is indicating the UTC -6 which is CST so whatever TimeZone is needed, the number and difference can be changed.

I ran into this issue running a GCP Cloud Function. Of course it works on a local machine, but running in the cloud makes the OS default (local) for new Date() irrelevant. In my case, an api call from the cloud required Eastern Standard Time, in ISO format (without the "Z") with offset as "-0500" or "-0400" depending on DST, for example:
2021-12-01T00:00:00.000-0500
Again, this is not a browser formatting issue, so I am forced into this format for the api call to work correctly.
Using #chickens code as a start, this is what worked:
var date = new Date();
var now_utc = Date.UTC(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(),
date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
var dt = new Date(now_utc);
let utcDate = new Date(dt.toLocaleString('en-US', { timeZone: "UTC" }));
let tzDate = new Date(dt.toLocaleString('en-US', { timeZone: "America/New_York" }));
let offset1 = utcDate.getTime() - tzDate.getTime();
let offset2 = offset1/60000;
let o1 = Math.abs(offset2);
console.log(offset2)
var offsetValue1 = (offset2 < 0 ? "+" : "-") + ("00" + Math.floor(o1 / 60)).slice(-2) + ("00" + (o1 % 60)).slice(-2);
console.log(offsetValue1)
dt.setTime(dt.getTime() - offset1);
console.log(dt.toISOString());
console.log(dt.toISOString().slice(0,-1)+offsetValue1);

I ran into a similar problem with unit tests (specifically in jest when the unit tests run locally to create the snapshots and then the CI server runs in (potentially) a different timezone causing the snapshot comparison to fail). I mocked our Date and some of the supporting methods like so:
describe('...', () => {
let originalDate;
beforeEach(() => {
originalDate = Date;
Date = jest.fn(
(d) => {
let newD;
if (d) {
newD = (new originalDate(d));
} else {
newD = (new originalDate('2017-05-29T10:00:00z'));
}
newD.toLocaleString = () => {
return (new originalDate(newD.valueOf())).toLocaleString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleDateString = () => {
return (new originalDate(newD.valueOf())).toLocaleDateString("en-US", {timeZone: "America/New_York"});
};
newD.toLocaleTimeString = () => {
return (new originalDate(newD.valueOf())).toLocaleTimeString("en-US", {timeZone: "America/New_York"});
};
return newD;
}
);
Date.now = () => { return (Date()); };
});
afterEach(() => {
Date = originalDate;
});
});

I had the same problem but we can use the time zone we want
we use .toLocaleDateString()
eg:
var day=new Date();
const options= {day:'numeric', month:'long', year:"numeric", timeZone:"Asia/Kolkata"};
const today=day.toLocaleDateString("en-IN", options);
console.log(today);

Try using ctoc from npm.
https://www.npmjs.com/package/ctoc_timezone
It has got simple functionality to change timezones (most timezones around 400) and all custom formats u want it to display.

Building on the answers above, I am using this native one liner to convert the long timezone string to the three letter string:
var longTz = 'America/Los_Angeles';
var shortTz = new Date().
toLocaleString("en", {timeZoneName: "short", timeZone: longTz}).
split(' ').
pop();
This will give PDT or PST depending on the date provided. In my particular use case, developing on Salesforce (Aura/Lightning), we are able to get the user timezone in the long format from the backend.

Thanks to #commonpike answer, I wrote a function which takes an ISO String date such as 2020-10-10T08:00:00.000 as input and send an object which contains 2 main properties.
The first one is fromUtc is a Date corresponding to the timeZone entered as parameter.
The second one is toUtc which lets you to format a Date stemming from fromUtc.
const timeZoneTransformer = (stringDate, timeZone = "Europe/Paris") => {
const now = new Date();
const serverDate = new Date(stringDate);
const utcDate = new Date(
Date.UTC(
serverDate.getFullYear(),
serverDate.getMonth(),
serverDate.getDate(),
serverDate.getHours(),
serverDate.getMinutes(),
serverDate.getSeconds()
)
);
const invdate = new Date(
serverDate.toLocaleString("en-US", {
timeZone,
})
);
const diff = now.getTime() - invdate.getTime();
const adjustedDate = new Date(now.getTime() - diff);
return {
toUtc: utcDate,
fromUtc: adjustedDate,
};
};
const fromUtc = timeZoneTransformer("2020-10-10T08:00:00.000").fromUtc;
console.log(fromUtc);
const toUtc = timeZoneTransformer(fromUtc).toUtc;
console.log(toUtc);

Try: date-from-timezone, it resolves expected date with help of natively available Intl.DateTimeFormat.
I used that method in one of my projects for few years already, but it's now I decided to publish it as small OS project :)

Try something like this,
public static getTimezoneOffset(timeZone: string, date = new Date()): number {
const localDate = date.toLocaleString('fr', { timeZone, timeZoneName: 'long' });
const tz = localDate.split(' ');
const TZ = localDate.replace(tz[0], '').replace(tz[1], '').replace(' ', '');
const dateString = date.toString();
const offset = (Date.parse(`${dateString} UTC`) - Date.parse(`${dateString}${TZ}`)) / (3600 * 1000);
return offset;
}

I'm not sure why all these answers are so complicated. Just use YYYY-MM-DD ZZZ when creating a date-only date in the local / desired time zone.
Create a local date:
var myDate = new Date('2022-11-29 CST')
The date will be stored in storage as UTC, great.
Get the date out of storage and display it as local:
myDate.toLocaleDateString()
11/29/2022

I know its 3 years too late, but maybe it can help someone else because I haven't found anything like that except for the moment-timezone library, which is not exactly the same as what he's asking for here.
I've done something similar for german timezone,
this is a little complex because of daylight saving time and leap years where you have 366 days.
it might need a little work with the "isDaylightSavingTimeInGermany" function while different timezones change on different times the daylight saving time.
anyway, check out this page:
https://github.com/zerkotin/german-timezone-converter/wiki
the main methods are:
convertLocalDateToGermanTimezone
convertGermanDateToLocalTimezone
I've put an effort into documenting it, so it won't be so confusing.

There are several working answers here, but somehow a lot of them seemed to get you to the string, but not back to a date object you started with, so here's my simple non-function take on how to change timezone on JS date:
var TZ='Australia/Brisbane'; //Target timezone from server
var date = new Date(); //Init this to a time if you don't want current time
date=new Date(Date.parse(date.toLocaleString("en-US", {timeZone: TZ})));
//Just a clarification on what happens
// 1) First new Date() gives you a Date object at current time in the clients browser local timezone
// 2) .toLocaleString takes that time, and returns a string if time in the target timezone
// 3) Date.parse converts that new string to a Unix epoch number
// 4) new Date() converts the Unix epoch into a Date object in the new TimeZone.
// Now I can use my usual getHours and other Date functions as required.
Hope that helps others (if you get to this bottom answer!)

Simple with Node.JS support
Pass in the amount of hours your timezone is offset from UTC
function initDateInTimezone(offsetHours) {
const timezoneOffsetInMS = offsetHours * 60 * 60000;
let d = new Date().getTimezoneOffset() * 60000 + timezoneOffsetInMS;
const date = new Date(new Date().getTime() - d);
return date
}

//For Mumbai time difference is 5.5 hrs so
city_time_diff=5.5; //change according to your city
let time_now = Date.now();
time_now = time_now + (3600000 * city_time_diff); //Add our city time (in msec);
let new_date = new Date(time_now);
console.log("My city time is: ", new_date);

Was facing the same issue, used this one
Console.log(Date.parse("Jun 13, 2018 10:50:39 GMT+1"));
It will return milliseconds to which u can check have +100 timzone intialize British time
Hope it helps!!

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