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How to convert utc time to local time on frontend [duplicate]

From the server I get a datetime variable in this format: 6/29/2011 4:52:48 PM and it is in UTC time. I want to convert it to the current user’s browser time zone using JavaScript.
How this can be done using JavaScript or jQuery?

Append 'UTC' to the string before converting it to a date in javascript:
var date = new Date('6/29/2011 4:52:48 PM UTC');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"

In my point of view servers should always in the general case return a datetime in the standardized ISO 8601-format.
More info here:
http://www.w3.org/TR/NOTE-datetime
https://en.wikipedia.org/wiki/ISO_8601
IN this case the server would return '2011-06-29T16:52:48.000Z' which would feed directly into the JS Date object.
var utcDate = '2011-06-29T16:52:48.000Z'; // ISO-8601 formatted date returned from server
var localDate = new Date(utcDate);
The localDate will be in the right local time which in my case would be two hours later (DK time).
You really don't have to do all this parsing which just complicates stuff, as long as you are consistent with what format to expect from the server.

This is an universal solution:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date.getTime()+date.getTimezoneOffset()*60*1000);
var offset = date.getTimezoneOffset() / 60;
var hours = date.getHours();
newDate.setHours(hours - offset);
return newDate;
}
Usage:
var date = convertUTCDateToLocalDate(new Date(date_string_you_received));
Display the date based on the client local setting:
date.toLocaleString();

For me above solutions didn't work.
With IE the UTC date-time conversion to local is little tricky.
For me, the date-time from web API is '2018-02-15T05:37:26.007' and I wanted to convert as per local timezone so I used below code in JavaScript.
var createdDateTime = new Date('2018-02-15T05:37:26.007' + 'Z');

You should get the (UTC) offset (in minutes) of the client:
var offset = new Date().getTimezoneOffset();
And then do the correspondent adding or substraction to the time you get from the server.
Hope this helps.

This works for me:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date.getTime() - date.getTimezoneOffset()*60*1000);
return newDate;
}

Put this function in your head:
<script type="text/javascript">
function localize(t)
{
var d=new Date(t+" UTC");
document.write(d.toString());
}
</script>
Then generate the following for each date in the body of your page:
<script type="text/javascript">localize("6/29/2011 4:52:48 PM");</script>
To remove the GMT and time zone, change the following line:
document.write(d.toString().replace(/GMT.*/g,""));

This is a simplified solution based on Adorjan Princ´s answer:
function convertUTCDateToLocalDate(date) {
var newDate = new Date(date);
newDate.setMinutes(date.getMinutes() - date.getTimezoneOffset());
return newDate;
}
or simpler (though it mutates the original date):
function convertUTCDateToLocalDate(date) {
date.setMinutes(date.getMinutes() - date.getTimezoneOffset());
return date;
}
Usage:
var date = convertUTCDateToLocalDate(new Date(date_string_you_received));

After trying a few others posted here without good results, this seemed to work for me:
convertUTCDateToLocalDate: function (date) {
return new Date(Date.UTC(date.getFullYear(), date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds()));
}
And this works to go the opposite way, from Local Date to UTC:
convertLocalDatetoUTCDate: function(date){
return new Date(date.getUTCFullYear(), date.getUTCMonth(), date.getUTCDate(), date.getUTCHours(), date.getUTCMinutes(), date.getUTCSeconds());
}

Add the time zone at the end, in this case 'UTC':
theDate = new Date( Date.parse('6/29/2011 4:52:48 PM UTC'));
after that, use toLocale()* function families to display the date in the correct locale
theDate.toLocaleString(); // "6/29/2011, 9:52:48 AM"
theDate.toLocaleTimeString(); // "9:52:48 AM"
theDate.toLocaleDateString(); // "6/29/2011"

if you have
"2021-12-28T18:00:45.959Z" format
you can use this in js :
// myDateTime is 2021-12-28T18:00:45.959Z
myDate = new Date(myDateTime).toLocaleDateString('en-US');
// myDate is 12/28/2021
myTime = new Date(myDateTime).toLocaleTimeString('en-US');
// myTime is 9:30:45 PM
you just have to put your area string instead of "en-US" (e.g. "fa-IR").
also you can use options for toLocaleTimeString like { hour: '2-digit', minute: '2-digit' }
myTime = new Date(myDateTime).toLocaleTimeString('en-US',{ hour: '2-digit', minute: '2-digit' });
// myTime is 09:30 PM
more information for toLocaleTimeString and toLocaleDateString

Use this for UTC and Local time convert and vice versa.
//Covert datetime by GMT offset
//If toUTC is true then return UTC time other wise return local time
function convertLocalDateToUTCDate(date, toUTC) {
date = new Date(date);
//Local time converted to UTC
console.log("Time: " + date);
var localOffset = date.getTimezoneOffset() * 60000;
var localTime = date.getTime();
if (toUTC) {
date = localTime + localOffset;
} else {
date = localTime - localOffset;
}
date = new Date(date);
console.log("Converted time: " + date);
return date;
}

Matt's answer is missing the fact that the daylight savings time could be different between Date() and the date time it needs to convert - here is my solution:
function ConvertUTCTimeToLocalTime(UTCDateString)
{
var convertdLocalTime = new Date(UTCDateString);
var hourOffset = convertdLocalTime.getTimezoneOffset() / 60;
convertdLocalTime.setHours( convertdLocalTime.getHours() + hourOffset );
return convertdLocalTime;
}
And the results in the debugger:
UTCDateString: "2014-02-26T00:00:00"
convertdLocalTime: Wed Feb 26 2014 00:00:00 GMT-0800 (Pacific Standard Time)

In case you don't mind usingmoment.js and your time is in UTC just use the following:
moment.utc('6/29/2011 4:52:48 PM').toDate();
if your time is not in utc but any other locale known to you, then use following:
moment('6/29/2011 4:52:48 PM', 'MM-DD-YYYY', 'fr').toDate();
if your time is already in local, then use following:
moment('6/29/2011 4:52:48 PM', 'MM-DD-YYYY');

To me the simplest seemed using
datetime.setUTCHours(datetime.getHours());
datetime.setUTCMinutes(datetime.getMinutes());
(i thought the first line could be enough but there are timezones which are off in fractions of hours)

This is what I'm doing to convert UTC to my Local Time:
const dataDate = '2020-09-15 07:08:08'
const utcDate = new Date(dataDate);
const myLocalDate = new Date(Date.UTC(
utcDate.getFullYear(),
utcDate.getMonth(),
utcDate.getDate(),
utcDate.getHours(),
utcDate.getMinutes()
));
document.getElementById("dataDate").innerHTML = dataDate;
document.getElementById("myLocalDate").innerHTML = myLocalDate;
<p>UTC<p>
<p id="dataDate"></p>
<p>Local(GMT +7)<p>
<p id="myLocalDate"></p>
Result: Tue Sep 15 2020 14:08:00 GMT+0700 (Indochina Time).

Using YYYY-MM-DD hh:mm:ss format :
var date = new Date('2011-06-29T16:52:48+00:00');
date.toString() // "Wed Jun 29 2011 09:52:48 GMT-0700 (PDT)"
For converting from the YYYY-MM-DD hh:mm:ss format, make sure your date follow the ISO 8601 format.
Year:
YYYY (eg 1997)
Year and month:
YYYY-MM (eg 1997-07)
Complete date:
YYYY-MM-DD (eg 1997-07-16)
Complete date plus hours and minutes:
YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00)
Complete date plus hours, minutes and seconds:
YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00)
Complete date plus hours, minutes, seconds and a decimal fraction of a second
YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00) where:
YYYY = four-digit year
MM = two-digit month (01=January, etc.)
DD = two-digit day of month (01 through 31)
hh = two digits of hour (00 through 23) (am/pm NOT allowed)
mm = two digits of minute (00 through 59)
ss = two digits of second (00 through 59)
s = one or more digits representing a decimal fraction of a second
TZD = time zone designator (Z or +hh:mm or -hh:mm)
Important things to note
You must separate the date and the time by a T, a space will not work in some browsers
You must set the timezone using this format +hh:mm, using a string for a timezone (ex. : 'UTC') will not work in many browsers. +hh:mm represent the offset from the UTC timezone.

A JSON date string (serialized in C#) looks like "2015-10-13T18:58:17".
In angular, (following Hulvej) make a localdate filter:
myFilters.filter('localdate', function () {
return function(input) {
var date = new Date(input + '.000Z');
return date;
};
})
Then, display local time like:
{{order.createDate | localdate | date : 'MMM d, y h:mm a' }}

For me, this works well
if (typeof date === "number") {
time = new Date(date).toLocaleString();
} else if (typeof date === "string"){
time = new Date(`${date} UTC`).toLocaleString();
}

I Answering This If Any one want function that display converted time to specific id element and apply date format string yyyy-mm-dd
here date1 is string and ids is id of element that time going to display.
function convertUTCDateToLocalDate(date1, ids)
{
var newDate = new Date();
var ary = date1.split(" ");
var ary2 = ary[0].split("-");
var ary1 = ary[1].split(":");
var month_short = Array('Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun', 'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec');
newDate.setUTCHours(parseInt(ary1[0]));
newDate.setUTCMinutes(ary1[1]);
newDate.setUTCSeconds(ary1[2]);
newDate.setUTCFullYear(ary2[0]);
newDate.setUTCMonth(ary2[1]);
newDate.setUTCDate(ary2[2]);
ids = document.getElementById(ids);
ids.innerHTML = " " + newDate.getDate() + "-" + month_short[newDate.getMonth() - 1] + "-" + newDate.getFullYear() + " " + newDate.getHours() + ":" + newDate.getMinutes() + ":" + newDate.getSeconds();
}
i know that answer has been already accepted but i get here cause of google and i did solve with getting inspiration from accepted answer so i did want to just share it if someone need.

#Adorojan's answer is almost correct. But addition of offset is not correct since offset value will be negative if browser date is ahead of GMT and vice versa.
Below is the solution which I came with and is working perfectly fine for me:
// Input time in UTC
var inputInUtc = "6/29/2011 4:52:48";
var dateInUtc = new Date(Date.parse(inputInUtc+" UTC"));
//Print date in UTC time
document.write("Date in UTC : " + dateInUtc.toISOString()+"<br>");
var dateInLocalTz = convertUtcToLocalTz(dateInUtc);
//Print date in local time
document.write("Date in Local : " + dateInLocalTz.toISOString());
function convertUtcToLocalTz(dateInUtc) {
//Convert to local timezone
return new Date(dateInUtc.getTime() - dateInUtc.getTimezoneOffset()*60*1000);
}

Based on #digitalbath answer, here is a small function to grab the UTC timestamp and display the local time in a given DOM element (using jQuery for this last part):
https://jsfiddle.net/moriz/6ktb4sv8/1/
<div id="eventTimestamp" class="timeStamp">
</div>
<script type="text/javascript">
// Convert UTC timestamp to local time and display in specified DOM element
function convertAndDisplayUTCtime(date,hour,minutes,elementID) {
var eventDate = new Date(''+date+' '+hour+':'+minutes+':00 UTC');
eventDate.toString();
$('#'+elementID).html(eventDate);
}
convertAndDisplayUTCtime('06/03/2015',16,32,'eventTimestamp');
</script>

You can use momentjs ,moment(date).format() will always give result in local date.
Bonus , you can format in any way you want. For eg.
moment().format('MMMM Do YYYY, h:mm:ss a'); // September 14th 2018, 12:51:03 pm
moment().format('dddd'); // Friday
moment().format("MMM Do YY");
For more details you can refer Moment js website

this worked well for me with safari/chrome/firefox :
const localDate = new Date(`${utcDate.replace(/-/g, '/')} UTC`);

I believe this is the best solution:
let date = new Date(objDate);
date.setMinutes(date.getTimezoneOffset());
This will update your date by the offset appropriately since it is presented in minutes.

tl;dr (new Date('6/29/2011 4:52:48 PM UTC')).toString()
The source string must specify a time zone or UTC.
One-liner:
(new Date('6/29/2011 4:52:48 PM UTC')).toString()
Result in one of my web browsers:
"Wed Jun 29 2011 09:52:48 GMT-0700 (Pacific Daylight Time)"
This approach even selects standard/daylight time appropriately.
(new Date('1/29/2011 4:52:48 PM UTC')).toString()
Result in my browser:
"Sat Jan 29 2011 08:52:48 GMT-0800 (Pacific Standard Time)"

using dayjs library:
(new Date()).toISOString(); // returns 2021-03-26T09:58:57.156Z (GMT time)
dayjs().format('YYYY-MM-DD HH:mm:ss,SSS'); // returns 2021-03-26 10:58:57,156 (local time)
(in nodejs, you must do before using it: const dayjs = require('dayjs');
in other environtments, read dayjs documentation.)

This works on my side
Option 1: If date format is something like "yyyy-mm-dd" or "yyyy-mm-dd H:n:s", ex: "2021-12-16 06:07:40"
With this format It doesnt really know if its a local format or a UTC time. So since we know that the date is a UTC we have to make sure that JS will know that its a UTC. So we have to set the date as UTC.
function setDateAsUTC(d) {
let date = new Date(d);
return new Date(
Date.UTC(
date.getFullYear(),
date.getMonth(),
date.getDate(),
date.getHours(),
date.getMinutes(),
date.getSeconds()
)
);
}
and then use it
let d = "2021-12-16 06:07:40";
setDateAsUTC(d).toLocaleString();
// output: 12/16/2021, 6:07:40 AM
Options 2: If UTC date format is ISO-8601. Mostly servers timestampz format are in ISO-8601 ex: '2011-06-29T16:52:48.000Z'. With this we can just pass it to the date function and toLocaleString() function.
let newDate = "2011-06-29T16:52:48.000Z"
new Date(newDate).toLocaleString();
//output: 6/29/2011, 4:52:48 PM

In JavaScript I used:
var updaated_time= "2022-10-25T06:47:42.000Z"
{{updaated_time | date: 'dd-MM-yyyy HH:mm'}} //output: 26-10-2022 12:00

I wrote a nice little script that takes a UTC epoch and converts it the client system timezone and returns it in d/m/Y H:i:s (like the PHP date function) format:
getTimezoneDate = function ( e ) {
function p(s) { return (s < 10) ? '0' + s : s; }
var t = new Date(0);
t.setUTCSeconds(e);
var d = p(t.getDate()),
m = p(t.getMonth()+1),
Y = p(t.getFullYear()),
H = p(t.getHours()),
i = p(t.getMinutes()),
s = p(t.getSeconds());
d = [d, m, Y].join('/') + ' ' + [H, i, s].join(':');
return d;
};

Material2 Datepicker - Convert date to timestamp without time [duplicate]

Can I convert iso date to milliseconds?
for example I want to convert this iso
2012-02-10T13:19:11+0000
to milliseconds.
Because I want to compare current date from the created date. And created date is an iso date.

Try this
var date = new Date("11/21/1987 16:00:00"); // some mock date
var milliseconds = date.getTime();
// This will return you the number of milliseconds
// elapsed from January 1, 1970
// if your date is less than that date, the value will be negative
console.log(milliseconds);
EDIT
You've provided an ISO date. It is also accepted by the constructor of the Date object
var myDate = new Date("2012-02-10T13:19:11+0000");
var result = myDate.getTime();
console.log(result);
Edit
The best I've found is to get rid of the offset manually.
var myDate = new Date("2012-02-10T13:19:11+0000");
var offset = myDate.getTimezoneOffset() * 60 * 1000;
var withOffset = myDate.getTime();
var withoutOffset = withOffset - offset;
console.log(withOffset);
console.log(withoutOffset);
Seems working. As far as problems with converting ISO string into the Date object you may refer to the links provided.
EDIT
Fixed the bug with incorrect conversion to milliseconds according to Prasad19sara's comment.

A shorthand of the previous solutions is
var myDate = +new Date("2012-02-10T13:19:11+0000");
It does an on the fly type conversion and directly outputs date in millisecond format.
Another way is also using parse method of Date util which only outputs EPOCH time in milliseconds.
var myDate = Date.parse("2012-02-10T13:19:11+0000");

Another option as of 2017 is to use Date.parse(). MDN's documentation points out, however, that it is unreliable prior to ES5.
var date = new Date(); // today's date and time in ISO format
var myDate = Date.parse(date);
See the fiddle for more details.

Yes, you can do this in a single line
let ms = Date.parse('2019-05-15 07:11:10.673Z');
console.log(ms);//1557904270673

Another possible solution is to compare current date with January 1, 1970, you can get January 1, 1970 by new Date(0);
var date = new Date();
var myDate= date - new Date(0);

Another solution could be to use Number object parser like this:
let result = Number(new Date("2012-02-10T13:19:11+0000"));
let resultWithGetTime = (new Date("2012-02-10T13:19:11+0000")).getTime();
console.log(result);
console.log(resultWithGetTime);
This converts to milliseconds just like getTime() on Date object

var date = new Date()
console.log(" Date in MS last three digit = "+ date.getMilliseconds())
console.log(" MS = "+ Date.now())
Using this we can get date in milliseconds

var date = new Date(date_string);
var milliseconds = date.getTime();
This worked for me!

if wants to convert UTC date to milliseconds
syntax : Date.UTC(year, month, ?day, ?hours, ?min, ?sec, ?milisec);
e.g :
date_in_mili = Date.UTC(2020, 07, 03, 03, 40, 40, 40);
console.log('miliseconds', date_in_mili);

In case if anyone wants to grab only the Time from a ISO Date, following will be helpful. I was searching for that and I couldn't find a question for it. So in case some one sees will be helpful.
let isoDate = '2020-09-28T15:27:15+05:30';
let result = isoDate.match(/\d\d:\d\d/);
console.log(result[0]);
The output will be the only the time from isoDate which is,
15:27

getTime() in AngularJS , error in new Date(date) in Java Script

$scope.notAvailableDayClick=function(val1,date){
console.log("day clcik")
var startDate=$filter('date')(date,'yyyy-MM-dd')
var endDate=new Date(startDate)
endDate.setMinutes(59)
endDate.setHours(23)
}
date is 2015-01-16
if I do this
new Date(date)
Thu Jan 15 2015 16:00:00 GMT-0800 (Pacific Standard Time)
So I have to go with AngularJS
var startDate=$filter('date')(date,'yyyy-MM-dd')
but now I need startDate.getTime(), error occur I think it takes it as a String

As per angular docs the filter returns a String in requested format. Date constructor accepts ISO8601 formats usually although some browsers support many formats as I remember. Probably your format yy-MM-dd is not supported.
I hope the variable date is a valid Date object, in that case why don't you use it instead of the formatted string you made with angular filter?
var endDate = new Date(date);
endDate.setMinutes(59);
endDate.setHours(23);
Also you have a Date constructor that accepts the format
new Date(year, month[, date[, hour[, minutes[, seconds[, milliseconds]]]]]);
So if what you have in hand is 2015-01-16 you can get midnight of that day with:
var startDate = "2015-01-16";
var year = parseInt(startDate.split('-')[0], 10);
var month = parseInt(startDate.split('-')[1], 10) - 1;
var year = parseInt(startDate.split('-')[2], 10);
var endDate = new Date(year, month, date, 23, 59);

Just use the original date to create endDate not the angular filtered version
var endDate=new Date(date);
endDate.setMinutes(59);
endDate.setHours(23);

Best option is to use ISO-String, because Google Chrome supports this format: MM-dd-yyyy. In Mozilla this format gives Invalid Date.
new Date('MM-dd-yyyy')
So using Iso-String in Angular, it can done as follows:
new Date($filter('date')(yourdDate,'yyyy-MM-ddTHH:mm:ss.sssZ'))

Comparing date time using javasctipt

I am trying to compare two dates using javascript,The datetime format is given below.Here i want to check date1 > date2.How can i achive this in javascript.
var date1='2014-03-25 07:30 AM';
var date2='2014-03-25 04:30 PM';

Use getTime:
if ((new Date(date1).getTime()) > ( new Date(date2).getTime())){
}

Like this -
if((new Date(date1).getTime()) > (new Date(date2).getTime())){
// do something
}

Please try this.
if (new Date(date1) > new Date(date2))

This should work:
var date1 = '2014-03-25 07:30 AM';
var date2 = '2014-03-25 04:30 PM';
console.log((new Date(date1)) >= (new Date(date2)));
EDIT:
Op correctly pointed out that the code above does not work (in FireFox, for example, but it works in Chrome). I have read that
new Date() // current date and time
new Date(milliseconds) //milliseconds since 1970/01/01
new Date(dateString)
new Date(year, month, day, hours, minutes, seconds, milliseconds)
are valid instantiations for Date here.
However, the date strings used for date1 and date2 in the example are not valid, therefore not supported in all browsers.
Instead of '2014-03-25 07:30 AM' (which is invalid) you should do one of the following:
convert your input into milliseconds
convert your input into date string, like "October 13, 1975 11:13:00"
calculate the year, month, day, hours, minutes, seconds and milliseconds, then pass them to the instantiation

How to the get the beginning of day of a date in javascript -- factoring in timezone

I am struggling to find out the beginning of day factoring in timezones in javascript. Consider the following:
var raw_time = new Date(this.created_at);
var offset_time = new Date(raw_hour.getTime() + time_zone_offset_in_ms);
// This resets timezone to server timezone
var offset_day = new Date(offset_time.setHours(0,0,0,0))
// always returns 2011-12-08 05:00:00 UTC, no matter what the offset was!
// This has the same issue:
var another_approach_offset_day = new Date(offset_time.getFullYear(),offset_time.getMonth(),offset_time.getHours())
I expect when i pass a Pacific Timezone offset, to get: 2011-12-08 08:00:00 UTC and so on.
What is the correct way to achieve this?
I think that part of the issue is that setHours method sets the hour (from 0 to 23), according to local time.
Also note that I am using javascript embedded in mongo, so I am unable to use any additional libraries.
Thanks!
Jeez, so this was really hard for me, but here is the final solution that I came up with the following solution. The trick was I need to use setHours or SetUTCHours to get the beginning of a day -- the only choices I have are system time and UTC. So I get the beginning of a UTC day, then add back the offset!
// Goal is given a time and a timezone, find the beginning of day
function(timestamp,selected_timezone_offset) {
var raw_time = new Date(timestamp)
var offset_time = new Date(raw_time.getTime() + selected_timezone_offset);
offset_time.setUTCHours(0,0,0,0);
var beginning_of_day = new Date(offset_time.getTime() - selected_timezone_offset);
return beginning_of_day;
}

In JavaScript all dates are stored as UTC. That is, the serial number returned by date.valueOf() is the number of milliseconds since 1970-01-01 00:00:00 UTC. But, when you examine a date via .toString() or .getHours(), etc., you get the value in local time. That is, the local time of the system running the script. You can get the value in UTC with methods like .toUTCString() or .getUTCHours(), etc.
So, you can't get a date in an arbitrary timezone, it's all UTC (or local). But, of course, you can get a string representation of a date in whatever timezone you like if you know the UTC offset. The easiest way would be to subtract the UTC offset from the date and call .getUTCHours() or .toUTCString() or whatever you need:
var d = new Date();
d.setMinutes(d.getMinutes() - 480); // get pacific standard time
d.toUTCString(); // returns "Fri, 9 Dec 2011 12:56:53 UTC"
Of course, you'll need to ignore that "UTC" at the end if you use .toUTCString(). You could just go:
d.toUTCString().replace(/UTC$/, "PST");
Edit: Don't worry about when timezones overlap date boundaries. If you pass setHours() a negative number, it will subtract those hours from midnight yesterday. Eg:
var d = new Date(2011, 11, 10, 15); // d represents Dec 10, 2011 at 3pm local time
d.setHours(-1); // d represents Dec 9, 2011 at 11pm local time
d.setHours(-24); // d represents Dec 8, 2011 at 12am local time
d.setHours(52); // d represents Dec 10, 2011 at 4am local time

Where does the time_zone_offset_in_ms variable you use come from? Perhaps it is unreliable, and you should be using Date's getTimezoneOffset() method. There is an example at the following URL:
http://www.w3schools.com/jsref/jsref_getTimezoneOffset.asp

If you know the date from a different date string you can do the following:
var currentDate = new Date(this.$picker.data('date'));
var today = new Date();
today.setHours(0, -currentDate.getTimezoneOffset(), 0, 0);
(based on the codebase for a project I did)

var aDate = new Date();
var startOfTheDay = new Date(aDate.getTime() - aDate.getTime() % 86400000)
Will create the beginning of the day, of the day in question

You can make use of Intl.DateTimeFormat. This is also how luxon handles timezones.
The code below can convert any date with any timezone to its beginging/end of the time.
const beginingOfDay = (options = {}) => {
const { date = new Date(), timeZone } = options;
const parts = Intl.DateTimeFormat("en-US", {
timeZone,
hourCycle: "h23",
hour: "numeric",
minute: "numeric",
second: "numeric",
}).formatToParts(date);
const hour = parseInt(parts.find((i) => i.type === "hour").value);
const minute = parseInt(parts.find((i) => i.type === "minute").value);
const second = parseInt(parts.find((i) => i.type === "second").value);
return new Date(
1000 *
Math.floor(
(date - hour * 3600000 - minute * 60000 - second * 1000) / 1000
)
);
};
const endOfDay = (...args) =>
new Date(beginingOfDay(...args).getTime() + 86399999);
const beginingOfYear = () => {};
console.log(beginingOfDay({ timeZone: "GMT" }));
console.log(endOfDay({ timeZone: "GMT" }));
console.log(beginingOfDay({ timeZone: "Asia/Tokyo" }));
console.log(endOfDay({ timeZone: "Asia/Tokyo" }));