We Keep Coding

Javascript Locale Date Conversions

I have a string coming into a function, this string is a date from Sweden and is formatted 2016 maj 01. Passed into this function is the country code for the locale sv-se. I need to convert the date string into a valid date object, to which I can then apply the locale.
This is for global date validation.
SO far I have
var date = new Date();
Intl.dateTimeFormat(locale, options).format(date);
I want to be able to have new Date("2016 maj 01") however since this is not English this is an invalid date. Can I using the locale convert this to a valid date object?
It was suggested my problem is similar to another. The way my problem is different is that I have the month coming in as the months abbreviated name. If the month was displayed numerically this would not be an issue

As I commented, it's probably a duplicate of an existing question. JavaScript Date object cannot be built from localized string.
However, you wan make your own Date builder from swedish:
Date.fromSwedish = (function() {
var months = {
'jan': 0,
'feb': 1,
'mar': 2,
'apr': 3,
'maj': 4 /*...*/
};
return function(s) {
var splitted = s.split(' ');
var year = splitted.length > 0 ? splitted[0] : 1970;
var month = splitted.length > 1 ? months[splitted[1].toLowerCase()] : 0 ;
var day = splitted.length > 2 ? splitted[2] : 1;
return new Date(year, month, day);
};
}());
document.write(Date.fromSwedish("2016") + "<br/>");
document.write(Date.fromSwedish("2016 feb") + "<br/>");
document.write(Date.fromSwedish("2016 maj 01") + "<br/>");

I think you are trying to do the opposite of the method Date.prototype.toLocaleDateString(), which returns formatted string based on the passed Locale and options arguments. You can read more about it here.
Now, here you want to do the opposite of what toLocaleDateString method does, you want to give a formatted date string with a Locale, and you expect it to return a date object. To do so, you can check this post, I hope it can help you to get a head start.
Also, if you are comfortable to use external libraries then you can explore for localization libraries like moment.js

Date formatting in moment.js , weird date values

So I have 2 kinds of date coming from json.
m = '201811';
n = '/Date(1433030400000)/';
I am trying to use moment.js to format time, but I can not find appropriate methods for it I guess.
moment(m).format('YYYY DD') //"201811 01"
and the n value I can not understand it leads to this output :
moment(m).format('YYYY DD')//"2015 31"

When you pass a date to moment() constructor, you might have to specify in what format it is.
So for the first date you would need to do:
moment(m, 'YYYYMM').format('YYYY MM'); // if the date is indeed in the form YYYYMM
For the second date, just extract the numeric part from the string and feed it to moment:
var ts = n.match(/(\d+)/);
moment(+ts[1]).format('YYYY DD');
See the snippet:
var m = '201811';
var n = '/Date(1433030400000)/';
alert(moment(m, 'YYYYMM').format('YYYY MM'));
var ts = n.match(/(\d+)/);
moment(+ts[1]).format('YYYY DD');
alert(moment(+ts[1]).format('YYYY MM'));
<script src="http://momentjs.com/downloads/moment.js"></script>
EDIT:
thanks to #MattJohnson, if you have at least moment version 1.3.0, you can simply pass the string in the form /Date(1433030400000)/ to the moment() constructor, and it will automatically detect the proper format, see also here.

Just pass them to moment in the following format:
var m = '201811';
var n = '/Date(1433030400000)/';
var formattedM = window.moment(m, 'YYYYMM').format('YYYY MMM DD'); //2018 Nov 01
var formattedN = window.moment(n).format('YYYY MMM DD'); //2015 May 31
I've dropped an example into jsbin.
Thanks to Matt Johnson for pointing out that moment can take the /Date(1433030400000)/ format.

Reading the date from textbox as a string and converting it into as Date

I am reading the date from textbox by using javascript and trying to convert it as Date object.But my problem is date is converting as month and month is converting as date when converting the string to date.
Example:
03/12/2014 the value in the textbox
Actual Output:
03 as March,
12 as date (Its wrong)
Expected Output:
03 as date
12 as December (I am expecting)
While converting this string to date by using following snippet
var startTime = document.getElementById("meeting:startTime");
date.js
var stringToDate_startTime=new Date(Date.parse(startTime.value,"dd/mm/yy"));
moment.js
var date1=moment(startTime.value).format('DD-MM-YYYY');
In the above even i have used date.js and moment.js files also.But those also did not solve my problem.Please can anyone help me out to get rid out of this.

Try ...
var from = startTime.value.split("/");
var newDate = newDate(from[2], from[1] - 1, from[0]);
... assuming time included ...
var date_only = startTime.value.split("");
var from = date_only[0].split("/");
var newDate = newDate(from[2], from[1] - 1, from[0]);

I am not aware of an implementation of the Date.parse() method that accepts two arguments. You can view the Mozilla Date.parse() method description here Date.parse() - JavaScript | MDN.
It might be worth looking at the question/answer of this question for some more information: Why does Date.parse give incorrect results?
The next best option would be to split the date using String.split() and to rearrange the date parts
var dateStr = '03/12/2014 23:05';
var newDateStr = null;
var dateParts = dateStr.split('/');
if (dateParts.length == 3) {
var day = dateParts[0];
var month = dateParts[1];
var yearAndTime = dateParts[2];
// Rearrange the month and day and rejoin the date "12/03/2014 23:05"
newDateStr = [ month, day, yearAndTime].join('/');
} else {
throw new Error('Date not in the expected format.');
}
var date = new Date(newDateStr); // JS Engine will parse the string automagically
alert(date);
This isn't the most elegant solution, but hopefully that helps.

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();

JSON Stringify changes time of date because of UTC

My date objects in JavaScript are always represented by UTC +2 because of where I am located. Hence like this
Mon Sep 28 10:00:00 UTC+0200 2009
Problem is doing a JSON.stringify converts the above date to
2009-09-28T08:00:00Z (notice 2 hours missing i.e. 8 instead of 10)
What I need is for the date and time to be honoured but it's not, hence it should be
2009-09-28T10:00:00Z (this is how it should be)
Basically I use this:
var jsonData = JSON.stringify(jsonObject);
I tried passing a replacer parameter (second parameter on stringify) but the problem is that the value has already been processed.
I also tried using toString() and toUTCString() on the date object, but these don't give me what I want either..
Can anyone help me?

Recently I have run into the same issue. And it was resolved using the following code:
x = new Date();
let hoursDiff = x.getHours() - x.getTimezoneOffset() / 60;
let minutesDiff = (x.getHours() - x.getTimezoneOffset()) % 60;
x.setHours(hoursDiff);
x.setMinutes(minutesDiff);

JSON uses the Date.prototype.toISOString function which does not represent local time -- it represents time in unmodified UTC -- if you look at your date output you can see you're at UTC+2 hours, which is why the JSON string changes by two hours, but if this allows the same time to be represented correctly across multiple time zones.

date.toJSON() prints the UTC-Date into a String formatted (So adds the offset with it when converts it to JSON format).
date = new Date();
new Date(date.getTime() - (date.getTimezoneOffset() * 60000)).toJSON();

Just for the record, remember that the last "Z" in "2009-09-28T08:00:00Z" means that the time is indeed in UTC.
See http://en.wikipedia.org/wiki/ISO_8601 for details.

Out-of-the-box solution to force JSON.stringify ignore timezones:
Pure javascript (based on Anatoliy answer):
// Before: JSON.stringify apply timezone offset
const date = new Date();
let string = JSON.stringify(date);
console.log(string);
// After: JSON.stringify keeps date as-is!
Date.prototype.toJSON = function(){
const hoursDiff = this.getHours() - this.getTimezoneOffset() / 60;
this.setHours(hoursDiff);
return this.toISOString();
};
string = JSON.stringify(date);
console.log(string);
Using moment + moment-timezone libraries:
const date = new Date();
let string = JSON.stringify(date);
console.log(string);
Date.prototype.toJSON = function(){
return moment(this).format("YYYY-MM-DDTHH:mm:ss:ms");;
};
string = JSON.stringify(date);
console.log(string);
<html>
<header>
<script src="https://momentjs.com/downloads/moment.min.js"></script>
<script src="https://momentjs.com/downloads/moment-timezone-with-data-10-year-range.min.js"></script>
</header>
</html>

Here is another answer (and personally I think it's more appropriate)
var currentDate = new Date();
currentDate = JSON.stringify(currentDate);
// Now currentDate is in a different format... oh gosh what do we do...
currentDate = new Date(JSON.parse(currentDate));
// Now currentDate is back to its original form :)

you can use moment.js to format with local time:
Date.prototype.toISOString = function () {
return moment(this).format("YYYY-MM-DDTHH:mm:ss");
};

I'm a little late but you can always overwrite the toJson function in case of a Date using Prototype like so:
Date.prototype.toJSON = function(){
return Util.getDateTimeString(this);
};
In my case, Util.getDateTimeString(this) return a string like this: "2017-01-19T00:00:00Z"

I run into this a bit working with legacy stuff where they only work on east coast US and don't store dates in UTC, it's all EST. I have to filter on the dates based on user input in the browser so must pass the date in local time in JSON format.
Just to elaborate on this solution already posted - this is what I use:
// Could be picked by user in date picker - local JS date
date = new Date();
// Create new Date from milliseconds of user input date (date.getTime() returns milliseconds)
// Subtract milliseconds that will be offset by toJSON before calling it
new Date(date.getTime() - (date.getTimezoneOffset() * 60000)).toJSON();
So my understanding is this will go ahead and subtract time (in milliseconds (hence 60000) from the starting date based on the timezone offset (returns minutes) - in anticipation for the addition of time toJSON() is going to add.

JavaScript normally convert local timezone to UTC .
date = new Date();
date.setMinutes(date.getMinutes()-date.getTimezoneOffset())
JSON.stringify(date)

Usually you want dates to be presented to each user in his own local time-
that is why we use GMT (UTC).
Use Date.parse(jsondatestring) to get the local time string,
unless you want your local time shown to each visitor.
In that case, use Anatoly's method.

Got around this issue by using the moment.js library (the non-timezone version).
var newMinDate = moment(datePicker.selectedDates[0]);
var newMaxDate = moment(datePicker.selectedDates[1]);
// Define the data to ask the server for
var dataToGet = {"ArduinoDeviceIdentifier":"Temperatures",
"StartDate":newMinDate.format('YYYY-MM-DD HH:mm'),
"EndDate":newMaxDate.format('YYYY-MM-DD HH:mm')
};
alert(JSON.stringify(dataToGet));
I was using the flatpickr.min.js library. The time of the resulting JSON object created matches the local time provided but the date picker.

Here is something really neat and simple (atleast I believe so :)) and requires no manipulation of date to be cloned or overloading any of browser's native functions like toJSON (reference: How to JSON stringify a javascript Date and preserve timezone, courtsy Shawson)
Pass a replacer function to JSON.stringify that stringifies stuff to your heart's content!!! This way you don't have to do hour and minute diffs or any other manipulations.
I have put in console.logs to see intermediate results so it is clear what is going on and how recursion is working. That reveals something worthy of notice: value param to replacer is already converted to ISO date format :). Use this[key] to work with original data.
var replacer = function(key, value)
{
var returnVal = value;
if(this[key] instanceof Date)
{
console.log("replacer called with key - ", key, " value - ", value, this[key]);
returnVal = this[key].toString();
/* Above line does not strictly speaking clone the date as in the cloned object
* it is a string in same format as the original but not a Date object. I tried
* multiple things but was unable to cause a Date object being created in the
* clone.
* Please Heeeeelp someone here!
returnVal = new Date(JSON.parse(JSON.stringify(this[key]))); //OR
returnVal = new Date(this[key]); //OR
returnVal = this[key]; //careful, returning original obj so may have potential side effect
*/
}
console.log("returning value: ", returnVal);
/* if undefined is returned, the key is not at all added to the new object(i.e. clone),
* so return null. null !== undefined but both are falsy and can be used as such*/
return this[key] === undefined ? null : returnVal;
};
ab = {prop1: "p1", prop2: [1, "str2", {p1: "p1inner", p2: undefined, p3: null, p4date: new Date()}]};
var abstr = JSON.stringify(ab, replacer);
var abcloned = JSON.parse(abstr);
console.log("ab is: ", ab);
console.log("abcloned is: ", abcloned);
/* abcloned is:
* {
"prop1": "p1",
"prop2": [
1,
"str2",
{
"p1": "p1inner",
"p2": null,
"p3": null,
"p4date": "Tue Jun 11 2019 18:47:50 GMT+0530 (India Standard Time)"
}
]
}
Note p4date is string not Date object but format and timezone are completely preserved.
*/

I ran into the same problem.
The way I resolvet it was:
var currentTime = new Date();
Console.log(currentTime); //Return: Wed Sep 15 13:52:09 GMT-05:00 2021
Console.log(JSON.stringify(currentTime)); //Return: "2021-09-15T18:52:09.891Z"
var currentTimeFixed = new Date(currentTime.setHours(currentTime.getHours() - (currentTime.getUTCHours() - currentTime.getHours())));
Console.log(JSON.stringify(currentTimeFixed)); //Return: "2021-09-15T13:52:09.891Z"

I wrote the following code blog where it makes service calls.. it will try to serializable the json in every post submission, it will format to local date it again.
protected async post(endPoint: string, data, panelName?: string, hasSuccessMessage: boolean = false): Promise<Observable<any>> {
const options = this.InitHeader(true);
const url: string = this._baseUrl + endPoint;
Date.prototype.toJSON = function () {
return moment(this).format("YYYY-MM-DDThh:mm:00.000Z");;
};
return await this._http.post(url, data, options).pipe(map(response => {
return this.Map<any>(response, null);
}));
}

All boils down to if your server backend is timezone-agnostic or not.
If it is not, then you need to assume that timezone of server is the same as client, or transfer information about client's timezone and include that also into calculations.
a PostgreSQL backend based example:
select '2009-09-28T08:00:00Z'::timestamp -> '2009-09-28 08:00:00' (wrong for 10am)
select '2009-09-28T08:00:00Z'::timestamptz -> '2009-09-28 10:00:00+02'
select '2009-09-28T08:00:00Z'::timestamptz::timestamp -> '2009-09-28 10:00:00'
The last one is probably what you want to use in database, if you are not willing properly implement timezone logic.

Instead of toJSON, you can use format function which always gives the correct date and time + GMT
This is the most robust display option. It takes a string of tokens
and replaces them with their corresponding values.

I tried this in angular 8 :
create Model :
export class Model { YourDate: string | Date; }
in your component
model : Model;
model.YourDate = new Date();
send Date to your API for saving
When loading your data from API you will make this :
model.YourDate = new Date(model.YourDate+"Z");
you will get your date correctly with your time zone.

In this case I think you need transform the date to UNIX timestamp
timestamp = testDate.getTime();
strJson = JSON.stringify(timestamp);
After that you can re use it to create a date object and format it. Example with javascript and toLocaleDateString ( https://developer.mozilla.org/fr/docs/Web/JavaScript/Reference/Objets_globaux/Date/toLocaleDateString )
newDateObject = new Date(JSON.parse(strJson));
newDateObject = newDateObject.toLocalDateStrin([
"fr-FR",
]);
If you use stringify to use AJAX, now it's not useful. You just need to send timestamp and get it in your script:
$newDateObject = new \DateTime();
$newDateObject->setTimestamp(round($timestamp/1000));
Be aware that getTime() will return a time in milliseconds and the PHP function setTimestamp take time in seconds. It's why you need to divide by 1000 and round.

In Angular place the following in index.js script section:
setTimeout(function (){
Date.prototype.toJSON = function(){
return new Date(this).toLocaleDateString("en-US") + " "+new Date(this).toLocaleTimeString();
}},1000);