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How to convert a date in specific timezone to utc

I am having a date string '2021-09-27 07:43' I also have the info that the date is in (GMT-8:00) Alaska time zone. I am in a different local timezone. When i convert this date to UTC , it is taking my timezone as the reference timezone.
const str = new Date().toLocaleString('en-US', { timeZone: 'Etc/GMT' });
How to do it with respect to a specific time zone as the reference rather than my local time?

You can convert it using moment.js.
see Example:
var input = '2021-09-27 07:43';
var fmt = 'YYYY-MM-DD HH:mm'; // must match the input
var zone = 'Etc/GMT';
var m = moment.tz(input, fmt, zone);
m.utc();
var s = m.format(fmt) // result:
console.log(s);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.18.1/moment.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment-timezone/0.5.11/moment-timezone-with-data-2010-2020.min.js"></script>

Try:
let myDate = "2021-09-27 07:43";
let myDateUTC = new Date(myDate + " UTC-8"); // 2021-09-27T15:43:00.000Z

why IsBefore moment js gives me false when should be true

My code is this:
const nowDate = moment(new Date()).format("DD/MM/YYYY");
let paraRepDate = '01/01/2021';
let calcParaDate = '30/06/2021';
var x = moment(calcParaDate).isBefore(nowDate)
console.log(x) // false
How is it possible?

Default format of momentjs is MM/DD/YYYY. In your solution you can see warning information in console:
Deprecation warning: value provided is not in a recognized RFC2822 or ISO format. moment construction falls back to js Date(), which is not reliable across all browsers and versions. Non RFC2822/ISO date formats are discouraged. Please refer to http://momentjs.com/guides/#/warnings/js-date/ for more info.
Solution
You have to specify format moment(date, format). Something like this:
const format = 'DD/MM/YYYY';
const nowDate = moment();
const calcParaDate = '30/06/2021';
const isBefore = moment(calcParaDate, format).isBefore(nowDate)
console.log(isBefore);
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment-with-locales.min.js" integrity="sha512-LGXaggshOkD/at6PFNcp2V2unf9LzFq6LE+sChH7ceMTDP0g2kn6Vxwgg7wkPP7AAtX+lmPqPdxB47A0Nz0cMQ==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>
Also you don't have to pass new Date() in moment() for current datetime.

Moment Js UTC to Local Time

I'm trying to convert UTC time to the local time. I've been following this example from this link: http://jsfiddle.net/FLhpq/4/light/. I can't seem to get the right local output. For example, if its 10: 30 am in here, instead of getting 10:30 ill get 15: 30. Here is my code:
var date = moment.utc().format('YYYY-MM-DD HH:mm:ss');
var localTime = moment.utc(date).toDate();
localTime = moment(localTime).format('YYYY-MM-DD HH:mm:ss');
console.log("moment: " + localTime);
No matter what I do the time always comes out at UTC time. I live in Houston so I know timezone is the issue. I've followed the code in the link but can seem to get the local time. What am I doing wrong?

To convert UTC time to Local you have to use moment.local().
For more info see docs
Example:
var date = moment.utc().format('YYYY-MM-DD HH:mm:ss');
console.log(date); // 2015-09-13 03:39:27
var stillUtc = moment.utc(date).toDate();
var local = moment(stillUtc).local().format('YYYY-MM-DD HH:mm:ss');
console.log(local); // 2015-09-13 09:39:27
Demo:
var date = moment.utc().format();
console.log(date, "- now in UTC");
var local = moment.utc(date).local().format();
console.log(local, "- UTC now to local");
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>

Try this:
let utcTime = "2017-02-02 08:00:13";
var local_date= moment.utc(utcTime).local().format('YYYY-MM-DD HH:mm:ss');

let utcTime = "2017-02-02 08:00:13.567";
var offset = moment().utcOffset();
var localText = moment.utc(utcTime).utcOffset(offset).format("L LT");
Try this JsFiddle

To convert UTC to local time
let UTC = moment.utc()
let local = moment(UTC).local()
Or you want directly get the local time
let local = moment()
var UTC = moment.utc()
console.log(UTC.format()); // UTC time
var cLocal = UTC.local()
console.log(cLocal.format()); // Convert UTC time
var local = moment();
console.log(local.format()); // Local time
<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.22.2/moment.min.js"></script>

Note: please update the date format accordingly.
Format Date
__formatDate: function(myDate){
var ts = moment.utc(myDate);
return ts.local().format('D-MMM-Y');
}
Format Time
__formatTime: function(myDate){
var ts = moment.utc(myDate);
return ts.local().format('HH:mm');
},

This is old question I see, but I didn't really get what I was looking for. I had a UTC datetime which was formatted without timezone. So I had to do this:
let utcDatetime = '2021-05-31 10:20:00';
let localDatetime = moment(utcDatetime + '+00:00').local().format('YYYY-MM-DD HH:mm:ss');

I've written this Codesandbox for a roundtrip from UTC to local time and from local time to UTC. You can change the timezone and the format. Enjoy!
Full Example on Codesandbox (DEMO):
https://codesandbox.io/s/momentjs-utc-to-local-roundtrip-foj57?file=/src/App.js

This is what worked for me, it required moment-tz as well as moment though.
const guess = moment.utc(date).tz(moment.tz.guess());
const correctTimezone = guess.format()

Here is what I do using Intl api:
let currentTimeZone = new Intl.DateTimeFormat().resolvedOptions().timeZone; // For example: Australia/Sydney
this will return a time zone name. Pass this parameter to the following function to get the time
let dateTime = new Date(date).toLocaleDateString('en-US',{ timeZone: currentTimeZone, hour12: true});
let time = new Date(date).toLocaleTimeString('en-US',{ timeZone: currentTimeZone, hour12: true});
you can also format the time with moment like this:
moment(new Date(`${dateTime} ${time}`)).format('YYYY-MM-DD[T]HH:mm:ss');

I've created one function which converts all the timezones into local time.
Requirements:
1. npm i moment-timezone
function utcToLocal(utcdateTime, tz) {
var zone = moment.tz(tz).format("Z") // Actual zone value e:g +5:30
var zoneValue = zone.replace(/[^0-9: ]/g, "") // Zone value without + - chars
var operator = zone && zone.split("") && zone.split("")[0] === "-" ? "-" : "+" // operator for addition subtraction
var localDateTime
var hours = zoneValue.split(":")[0]
var minutes = zoneValue.split(":")[1]
if (operator === "-") {
localDateTime = moment(utcdateTime).subtract(hours, "hours").subtract(minutes, "minutes").format("YYYY-MM-DD HH:mm:ss")
} else if (operator) {
localDateTime = moment(utcdateTime).add(hours, "hours").add(minutes, "minutes").format("YYYY-MM-DD HH:mm:ss")
} else {
localDateTime = "Invalid Timezone Operator"
}
return localDateTime
}
utcToLocal("2019-11-14 07:15:37", "Asia/Kolkata")
//Returns "2019-11-14 12:45:37"

How to convert Moment.js date to users local timezone?

I use the Moment.js and Moment-Timezone frameworks, and have a Moment.js date object which is explicitly in UTC timezone. How can I convert that to the current timezone of the browser?
var testDateUtc = moment.tz("2015-01-30 10:00:00", "UTC");
var localDate = ???
So it would be fine if I could find out the users local time zone; or alternatively I'd like to convert the date object into another data object which just uses the "local timezone", no matter what that actually is.

You do not need to use moment-timezone for this. The main moment.js library has full functionality for working with UTC and the local time zone.
var testDateUtc = moment.utc("2015-01-30 10:00:00");
var localDate = moment(testDateUtc).local();
From there you can use any of the functions you might expect:
var s = localDate.format("YYYY-MM-DD HH:mm:ss");
var d = localDate.toDate();
// etc...
Note that by passing testDateUtc, which is a moment object, back into the moment() constructor, it creates a clone. Otherwise, when you called .local(), it would also change the testDateUtc value, instead of just the localDate value. Moments are mutable.
Also note that if your original input contains a time zone offset such as +00:00 or Z, then you can just parse it directly with moment. You don't need to use .utc or .local. For example:
var localDate = moment("2015-01-30T10:00:00Z");

var dateFormat = 'YYYY-DD-MM HH:mm:ss';
var testDateUtc = moment.utc('2015-01-30 10:00:00');
var localDate = testDateUtc.local();
console.log(localDate.format(dateFormat)); // 2015-30-01 02:00:00
Define your date format.
Create a moment object and set the UTC flag to true on the object.
Create a localized moment object converted from the original moment
object.
Return a formatted string from the localized moment object.
See: http://momentjs.com/docs/#/manipulating/local/

Here's what I did:
var timestamp = moment.unix({{ time }});
var utcOffset = moment().utcOffset();
var local_time = timestamp.add(utcOffset, "minutes");
var dateString = local_time.fromNow();
Where {{ time }} is the utc timestamp.

Use utcOffset function.
var testDateUtc = moment.utc("2015-01-30 10:00:00");
var localDate = moment(testDateUtc).utcOffset(10 * 60); //set timezone offset in minutes
console.log(localDate.format()); //2015-01-30T20:00:00+10:00

class Time extends React.Component {
constructor(props) {
super(props)
this.state = {
parentTime: '',
localTime: '',
parentTz: ''
}
}
componentDidMount() {
const inputTz = "America/Toronto"
const originTime = "2013-11-18 11:55"
const time = moment.tz(originTime, inputTz)
const localtz = moment.tz.guess()
const date = time.clone().tz(localtz)
const formatDate = moment(date).format('MMMM Do YYYY, h:mm:ss A z')
console.log(formatDate, localtz)
this.setState({parentTime: originTime, localTime: formatDate, parentTz: inputTz })
}
render() {
const {parentTime, parentTz, localTime} = this.state
return (
<div>
<p>{parentTime}<br/> in {parentTz}<br/> to {localTime}</p>
</div>
)
}
}
ReactDOM.render(
<Time />,
document.getElementById('time')
);
<script src="https://momentjs.com/downloads/moment.js"></script>
<script src="https://momentjs.com/downloads/moment-timezone.js"></script>
<script src="https://momentjs.com/downloads/moment-timezone-with-data-1970-2030.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.3.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react-dom/15.3.0/react-dom.min.js"></script>
<div id="time"></div>
the best way to get a user's time zone is using moment-timezone
import moment from 'moment-timezone'
// using utc time here
const time = moment.tz("2021-04-14T02:08:10.370Z")
const localtz = moment.tz.guess()
const date = time.clone().tz(localtz)
const formatDate = moment(date).format('MMMM Do YYYY, h:mm:ss A z')
console.log(formatDate)
this way you will be able to convert your time into a local timezone specific time

Convert date to UTC using moment.js

Probably and easy answer to this but I can't seem to find a way to get moment.js to return a UTC date time in milliseconds. Here is what I am doing:
var date = $("#txt-date").val(),
expires = moment.utc(date);
Any idea what I am doing wrong?

This is found in the documentation. With a library like moment, I urge you to read the entirety of the documentation. It's really important.
Assuming the input text is entered in terms of the users's local time:
var expires = moment(date).valueOf();
If the user is instructed actually enter a UTC date/time, then:
var expires = moment.utc(date).valueOf();

I use this method and it works. ValueOf does not work for me.
moment.utc(yourDate).format()

As of : moment.js version 2.24.0
let's say you have a local date input, this is the proper way to convert your dateTime or Time input to UTC :
var utcStart = new moment("09:00", "HH:mm").utc();
or in case you specify a date
var utcStart = new moment("2019-06-24T09:00", "YYYY-MM-DDTHH:mm").utc();
As you can see the result output will be returned in UTC :
//You can call the format() that will return your UTC date in a string
utcStart.format();
//Result : 2019-06-24T13:00:00
But if you do this as below, it will not convert to UTC :
var myTime = new moment.utc("09:00", "HH:mm");
You're only setting your input to utc time, it's as if your mentioning that myTime is in UTC, ....the output will be 9:00

This will be the answer:
moment.utc(moment(localdate)).format()
localdate = '2020-01-01 12:00:00'
moment(localdate)
//Moment<2020-01-01T12:00:00+08:00>
moment.utc(moment(localdate)).format()
//2020-01-01T04:00:00Z

moment.utc(date).format(...);
is the way to go, since
moment().utc(date).format(...);
does behave weird...

This worked for me. Others might find it useful.
let date = '2020-08-31T00:00:00Z'
moment.utc(moment(date).utc()).format() // returns 2020-08-30T22:00:00Z

If all else fails, just reinitialize with an inverse of your local offset.
var timestamp = new Date();
var inverseOffset = moment(timestamp).utcOffset() * -1;
timestamp = moment().utcOffset( inverseOffset );
timestamp.toISOString(); // This should give you the accurate UTC equivalent.

This moment.utc(stringDate, format).toDate() worked for me.
This moment.utc(date).toDate() not.

here, I'm passing the date object and converting it into UTC time.
$.fn.convertTimeToUTC = function (convertTime) {
if($(this).isObject(convertTime)) {
return moment.tz(convertTime.format("Y-MM-DD HH:mm:ss"), moment.tz.guess()).utc().format("Y-MM-DD HH:mm:ss");
}
};
// Returns if a value is an object
$.fn.isObject = function(value) {
return value && typeof value === 'object';
};
//you can call it as below
$(this).convertTimeToUTC(date);

Read this documentation of moment.js here.
See below example and output where I convert GMT time to local time (my zone is IST) and then I convert local time to GMT.
// convert GMT to local time
console.log('Server time:' + data[i].locationServerTime)
let serv_utc = moment.utc(data[i].locationServerTime, "YYYY-MM-DD HH:mm:ss").toDate();
console.log('serv_utc:' + serv_utc)
data[i].locationServerTime = moment(serv_utc,"YYYY-MM-DD HH:mm:ss").tz(self.zone_name).format("YYYY-MM-DD HH:mm:ss");
console.log('Converted to local time:' + data[i].locationServerTime)
// convert local time to GMT
console.log('local time:' + data[i].locationServerTime)
let serv_utc = moment(data[i].locationServerTime, "YYYY-MM-DD HH:mm:ss").toDate();
console.log('serv_utc:' + serv_utc)
data[i].locationServerTime = moment.utc(serv_utc,"YYYY-MM-DD HH:mm:ss").format("YYYY-MM-DD HH:mm:ss");
console.log('Converted to server time:' + data[i].locationServerTime)
Output is
Server time:2019-12-19 09:28:13
serv_utc:Thu Dec 19 2019 14:58:13 GMT+0530 (India Standard Time)
Converted to local time:2019-12-19 14:58:13
local time:2019-12-19 14:58:13
serv_utc:Thu Dec 19 2019 14:58:13 GMT+0530 (India Standard Time)
Converted to server time:2019-12-19 09:28:13

This worked for me:
const localtime = 1622516400000
moment(localtime).utc(true).format()

We can get 2 UTC date formats.
const date = '2021-07-20T18:30:00Z';
moment.utc(moment(date).utc()).format(); // 2021-07-19T18:30:00Z
moment.utc(moment(date).utc()).toISOString(); // 2021-07-20T18:30:00.000Z (Complete ISO-8601)

This works in my case.
Library: "moment": "^2.29.1",
moment().utc().format()

Don't you need something to compare and then retrieve the milliseconds?
For instance:
let enteredDate = $("#txt-date").val(); // get the date entered in the input
let expires = moment.utc(enteredDate); // convert it into UTC
With that you have the expiring date in UTC.
Now you can get the "right-now" date in UTC and compare:
var rightNowUTC = moment.utc(); // get this moment in UTC based on browser
let duration = moment.duration(rightNowUTC.diff(expires)); // get the diff
let remainingTimeInMls = duration.asMilliseconds();