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Initializing time with its own timezone

I'm quite new (and confused) with time in JavaScript..
I currently have time data to work with, and they are in the format of DD-MMM-YYYY, meaning it would be 23-Feb-2021. This time is already in its own timezone, GMT-10. I'm trying to initialize it as GMT-10 so that I could get its appropriate epoch time.
I've done this:
date = new Date("23-Feb-2021") // This results in 2021-02-23T00:00:00.000Z
But what I'm trying to achieve is to get the time to be 2021-02-23T10:00:00.000Z, which I could then do a getTime() to get its epoch in ms. I understand I could probably hard code to +10 to the time I have, but the data I work with might vary so I'd like to figure a way to initialize the date with a specific timezone.
EDIT:
Here's an example of an outcome I'd want:
date = ("23-Feb-2021")
date = moment(date).format(); // 2021-02-23T00:00:00+00:00
date = date.replace("+00","+10");
date = new Date(msg.date); // 2021-02-22T14:00:00.000Z
date = date.getTime(); // 1614002400000 (2021-02-22T14:00:00.000Z)
In the end, 2021-02-22T14:00:00.000Z is what I'm trying to get, without having to iterate it a bunch of times like above and adding +10

You can add the timezone offset to your input string, and use an explicit string format to parse it:
let date = "23-Feb-2021"
date = moment(date + "-10:00", "D-MMM-YYYYZ")
console.log(date.format()) // 2021-02-23T11:00:00+01:00 (if local is GMT+1)
console.log(date.utc().format()) // 2021-02-23T10:00:00+00:00

It seems you're already using moment.js, so add moment–timezone so you can parse timestamps in whatever IANA timezone you want. You can either choose a location with the offset rules you want (e.g. Pacific/Honolulu or Pacific/Tahiti for -10) or just a fixed offset like etc/GMT+10.
You can then format the value in any timezone, as UTC, or as a time value, e.g.
// Timestamp
let d = "23-Feb-2021";
// Parse in specific IANA timezone
let m = moment.tz(d, 'D-MMM-YYYY', 'Pacific/Honolulu');
// Trigger UTC mode
m.utc()
// Show result
console.log(m.format())
// Get time value (ms since epoch)
console.log(m.valueOf());
// Parse using generic timezone/fixed offset
let g = moment.tz(d, 'D-MMM-YYYY', 'etc/GMT+10');
console.log(g.utc().format());
// Display timestamp for another timezone
console.log(moment.tz(g, 'Asia/Riyadh').format());
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.4/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment-timezone/0.5.34/moment-timezone-with-data-10-year-range.js"></script>
Note that for fixed offset timezones like etc/GMT+10, the sign is the opposite of the common offset (e.g. etc/GMT+10 is UTC-10) to be consistent with POSIX notation. However, moment.tz only has limited POSIX support in that it only recognises one hour offsets, not the full POSIX timezone notation, so you can't do say "etc/GMT-530" instead of Asia/Kolkata.

How to display times in different time zones using the offset value

I am trying to display the current moment in different time zones. I have tried to use native javascript and the moment-js package but it seems you require the time zone name (ex. "America/Toronto") to display the information I want. The problem is that the information I currently have is the timestamp in string format (see below for string format) from the desired timezone, and the city the timestamp belongs to. The problem with using the city to create my tz value is that one of the cities I want to display isn't in the IANA tz database (Calgary).
String timestamp:
2022-04-26T14:19:42.8430964-04:00
As can be seen I do have the time offset and I was hoping there was a way to convert this string in js to a Date object and then display the time using the offset in the correct time zone.
Note what I want to display is the following format:
12:19 pm MT
I know I could just parse out the string but I feel like this isn't the best practice, however I may be wrong.
Also note that I will have to get the time zone (ex. MT, ET it can also be MST, EST) using the offset.

you don't need moment here. JS can do this natively. Also moment is now deprecated.
Your IANA timezone is America/Edmonton. So it's simple to do. That date format is an ISO 8601 date format, so you can just pass it into the new Date constructor and it'll parse it correctly:
const iso8601 = '2022-04-26T14:19:42.8430964-04:00';
const date = new Date(iso8601);
console.log(date.toLocaleString('en-US', { timeZone: 'America/Edmonton' }));
It doesn't matter what timezone your input date is set, so long as it has the correct offset in the ISO date. Once it's a Date, the offset is irrelevant. E.g.:
const iso8601 = '2022-04-26T14:19:42.8430964Z';
const date = new Date(iso8601);
//time will now be 4 hours off above as the input date is UTC
console.log(date.toLocaleString('en-US', { timeZone: 'America/Edmonton' }));

How to add timezone offset to string without changing the time?

I have a time string like this 2021-12-29T01:30:00.105Z. I want to add offset for a timezone without changing the date and time. So it should look like this after conversion - 2021-12-29T01:30:00+08:00 for "Asia/Kuala_Lumpur" timezone.
So 2021-12-29T01:30:00.105Z -> 2021-12-29T01:30:00+08:00
I cannot do a string replace since the timezone will be dynamic and does not always has to be "Asia/Kuala_Lumpur".
I am using moment and moment-timezone libraries and have tried different ways to get the required result but none seems to work.
Please help.

If you have the IANA name for the timezone and you want to change the timezone of a date in +XX:XX format without modifying the time, you can calculate the offset and replace it in the string:
const timeString = '2021-12-29T01:30:00.105Z';
const timezone = 'Asia/Kuala_Lumpur';
const offset = Intl.DateTimeFormat([], {timeZone: timezone, timeZoneName: 'longOffset'}).formatToParts().find(o => o.type === 'timeZoneName').value.match(/\+.*$/)[0];
const newTimeString = timeString.replace(/\..+Z$/, offset);
console.log(timeString);
console.log(newTimeString);

Set timezone in javascript without toLocaleString

I want to set a timezone to a date. So basically a date should be display everytime taking into account that timezone. Also i want to use a native solution.
I know that exists this solution:
const t = new Date(1641991591447).toLocaleString('en-GB', { timeZone: 'Europe/London' })
console.log(t)
But this returns 12/01/2022, 12:46:31 instead of 2022-01-12T12:46:31.447Z this format. So how to get the last format taking into account the timezone?

In order to convert your date to the specified format (ISO date string), you can do this by simply creating a Date constructor and using your date value as the input and chaining the toISOString method to it.
const t = new Date(1641991591447).toISOString(); // 2022-12-01T12:46:31.000Z

Parse JSON DateTime object to local time in JQuery by ignoring timezone

I am facing an issue while parsing JSON Date Time object using moment(of course I tried many approaches suggested in Stackoverflow but nothing worked in my case).
In my application, I'm storing a DateTime value as UTC DateTime. Now when I'm displaying I need to display it according to the browser timezone. After going through many StackOverflow questions, I used "moment.js" as below
//From server, the Date object looks like /Date(1506510057813)/
//The equivalent DateTime value stored in Database is 2017-09-27 13:00:57.813
fuction DateTimeFormatter(value)
{
if (value != undefined) {
var newValue = new Date(moment.utc(value));
//But at this line, even with just moment(value) all I am getting is DateTime which is not same as UTC time.
//I don't want any time zone to get appended all I want is just 13:00:57
var newHours = newValue.getHours() - newValue.getTimezoneOffset() / 60;
var newMinutes = (newHours + '.0').split('.')[1] * 6;
newValue.setHours(newHours);
newValue.setMinutes(newMinutes);
return moment(newValue).format(applicationTableDateFormat);
}
else
return "";
}
Please let me know what I am doing wrong or is there any other way I can display time as per browser time zone.

Once you have a UTC moment, you can convert it to local.
moment.utc(value).local().format(...)
https://momentjs.com/docs/#/manipulating/local/
But it sounds like maybe your real problem is when you store the date. If you're storing it as UTC, make sure you actually convert the local value to UTC before you store it. That way when you read it, you get a predictable value that you can safely convert to any locale.

Angularjs has its own mechanism to display formatted dates on views you just needs an absolute representation of a date and it takes care of the rest. And by absolute, I mean, a Date which is settled in a timezone whether it's utc or not, you need to know what timezone you are talking about.
The date filter
It's a filter from the core module of angularjs and it accepts:
"... either as Date object, milliseconds (string or number) or various ISO 8601 datetime string formats (e.g. yyyy-MM-ddTHH:mm:ss.sssZ and its shorter versions like yyyy-MM-ddTHH:mmZ, yyyy-MM-dd or yyyyMMddTHHmmssZ). If no timezone is specified in the string input, the time is considered to be in the local timezone." (Angularjs date filter)
The problem
Angularjs need a proper date input in order to display it correctly, in your case you seem to have the milliseconds format (sort of, /Date(1506510057813)/), you could use that and extract the numeric part and input that on the pipe, or you can change the server to send the ISO 8601 date (a.k.a., yyyy-MM-ddTHH:mm:ss.sssZ).
For example:
let rawDate = '/Date(1506510057813)/';
let re = /\/Date\((\d+)\)\//g; // regex to extract number from the string date
let myDate = new Date(Number(re.exec()[1])) // extract the milliseconds
Or
let rawDate = '2017-09-27T11:00:57.813Z';
let myDate = new Date(rawDate)// and you don't need to do anything else
Either way you'd end up with something like this:
<span> {{ myDate | date }}</span>