Suppose a user of your website enters a date range.
2009-1-1 to 2009-1-3
You need to send this date to a server for some processing, but the server expects all dates and times to be in UTC.
Now suppose the user is in Alaska. Since they are in a timezone quite different from UTC, the date range needs to be converted to something like this:
2009-1-1T8:00:00 to 2009-1-4T7:59:59
Using the JavaScript Date object, how would you convert the first "localized" date range into something the server will understand?
Simple and stupid
var date = new Date();
var now_utc = Date.UTC(date.getUTCFullYear(), date.getUTCMonth(),
date.getUTCDate(), date.getUTCHours(),
date.getUTCMinutes(), date.getUTCSeconds());
console.log(new Date(now_utc));
console.log(date.toISOString());
The toISOString() method returns a string in simplified extended ISO
format (ISO 8601), which is always 24 or 27 characters long
(YYYY-MM-DDTHH:mm:ss.sssZ or ±YYYYYY-MM-DDTHH:mm:ss.sssZ,
respectively). The timezone is always zero UTC offset, as denoted by
the suffix "Z".
Source: MDN web docs
The format you need is created with the .toISOString() method. For older browsers (ie8 and under), which don't natively support this method, the shim can be found here:
This will give you the ability to do what you need:
var isoDateString = new Date().toISOString();
console.log(isoDateString);
For Timezone work, moment.js and moment.js timezone are really invaluable tools...especially for navigating timezones between client and server javascript.
Here's my method:
var now = new Date();
var utc = new Date(now.getTime() + now.getTimezoneOffset() * 60000);
The resulting utc object isn't really a UTC date, but a local date shifted to match the UTC time (see comments). However, in practice it does the job.
Update: This answer is a quick-and-dirty way to get the UTC date when calling utc.toString(), utc.toLocaleString(), etc. Though, there are better solutions, in particular nowadays with modern browsers, and I should work on an improved answer. Basically, now.toISOString() (IE 9+) is what you want to use.
Convert to ISO without changing date/time
var now = new Date(); // Fri Feb 20 2015 19:29:31 GMT+0530 (India Standard Time)
var isoDate = new Date(now.getTime() - now.getTimezoneOffset() * 60000).toISOString();
//OUTPUT : 2015-02-20T19:29:31.238Z
Convert to ISO with change in date/time(date/time will be changed)
isoDate = new Date(now).toISOString();
//OUTPUT : 2015-02-20T13:59:31.238Z
Fiddle link
Date.prototype.toUTCArray= function(){
var D= this;
return [D.getUTCFullYear(), D.getUTCMonth(), D.getUTCDate(), D.getUTCHours(),
D.getUTCMinutes(), D.getUTCSeconds()];
}
Date.prototype.toISO= function(){
var tem, A= this.toUTCArray(), i= 0;
A[1]+= 1;
while(i++<7){
tem= A[i];
if(tem<10) A[i]= '0'+tem;
}
return A.splice(0, 3).join('-')+'T'+A.join(':');
}
Another solution to convert to UTC and keep it as a date object:
(It works by removing the ' GMT' part from the end of the formatted string, then putting it back into the Date constructor)
const now = new Date();
const now_utc = new Date(now.toUTCString().slice(0, -4));
console.log(now_utc.toString()); // ignore the timezone
I needed to do this to interface with a datetime picker library. But in general it's a bad idea to work with dates this way.
Users generally want to work with datetimes in their local time, so you either update the server side code to parse datetime strings with offsets correctly, then convert to UTC (best option) or you convert to a UTC string client-side before sending to the server (like in Will Stern's answer)
Browsers may differ, and you should also remember to not trust any info generated by the client, that being said, the below statement works for me (Google Chrome v24 on Mac OS X 10.8.2)
var utcDate = new Date(new Date().getTime());
edit: "How is this different than just new Date()?" see here: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date
If no arguments are provided, the constructor creates a JavaScript Date object for the current date and time according to system settings.
Note: Where Date is called as a constructor with more than one argument, the specifed arguments represent local time. If UTC is desired, use new Date(Date.UTC(...)) with the same arguments. (note: Date.UTC() returns the number of millisecond since 1970-01-01 00:00:00 UTC)
Adding the 60000 * Date.getTimezoneOffset() as previous answers have stated is incorrect. First, you must think of all Dates/Times as already being UTC with a timezone modifier for display purposes.
Again, browsers may differ, however, Date.getTime() returns the number of milliseconds since 1970-01-01 UTC/GMT. If you create a new Date using this number as I do above, it will be UTC/GMT. However, if you display it by calling .toString() it will appear to be in your local timezone because .toString() uses your local timezone, not the timezone of the Date object it is called on.
I have also found that if you call .getTimezoneOffset() on a date, it will return your local timezone, not the timezone of the date object you called it on (I can't verify this to be standard however).
In my browser, adding 60000 * Date.getTimezoneOffset() creates a DateTime that is not UTC. However when displayed within my browser (ex: .toString() ), it displays a DateTime in my local timezone that would be correct UTC time if timezone info is ignored.
My solution keeps the date the same no matter what timezone is set on the client-side. Maybe someone will find it useful.
My use case:
I'm creating a todo app, where you set date of your task. This date should remain constant no matter what timezone you're in.
Example. You want to call your friend at 8 am on June 25th.
You create this task 5 days before (June 20th) while you're in China.
Then, on the same day, you fly to New York for a few days.
Then on June 25th, while you're still in New York, you wake up at 7:30 am (which means you should receive task notification in 30 mins (even tho it's 1:30 pm already in China where you were when creating the task)
So the task is ignoring the timezone. It means 'I want to do it at 8 am in whatever timezone I'll be in'.
What I do is let's say 'I assume you're always in London Timezone - UTC'.
What it means is - when the user picks some date in her/his Timezone - I convert this date to the same date in UTC. ie. You pick 8 am in China, but I convert it to 8 am in UTC.
Then - next time you open the app - I read the date saved in UTC and convert it to the same date in your current timezone - eg. I convert 8 am in UTC to 8 am in the New York timezone.
This solution means that the date can mean something else depending on where you are when setting it and where you're reading it, but it remains constant in a way that it 'feels' like you're always in the same timezone.
Let's write some code:
First - we have 2 main functions for converting from/to UTC ignoring timezone:
export function convertLocalDateToUTCIgnoringTimezone(date: Date) {
const timestamp = Date.UTC(
date.getFullYear(),
date.getMonth(),
date.getDate(),
date.getHours(),
date.getMinutes(),
date.getSeconds(),
date.getMilliseconds(),
);
return new Date(timestamp);
}
export function convertUTCToLocalDateIgnoringTimezone(utcDate: Date) {
return new Date(
utcDate.getUTCFullYear(),
utcDate.getUTCMonth(),
utcDate.getUTCDate(),
utcDate.getUTCHours(),
utcDate.getUTCMinutes(),
utcDate.getUTCSeconds(),
utcDate.getUTCMilliseconds(),
);
}
Then, I save/read this date like:
function saveTaskDate(localDate: Date) {
// I convert your local calendar date so it looks like you've picked it being in UTC somewhere around London
const utcDate = convertLocalDateToUTCIgnoringTimezone(localDate);
api.saveTaskDate(utcDate);
}
function readTaskDate(taskUtcDate: Date) {
// I convert this UTC date to 'look in your local timezone' as if you were now in UTC somewhere around london
const localDateWithSameDayAsUTC = convertUTCToLocalDateIgnoringTimezone(taskUtcDate);
// this date will have the same calendar day as the one you've picked previously
// no matter where you were saving it and where you are now
}
var myDate = new Date(); // Set this to your date in whichever timezone.
var utcDate = myDate.toUTCString();
Are you trying to convert the date into a string like that?
I'd make a function to do that, and, though it's slightly controversial, add it to the Date prototype. If you're not comfortable with doing that, then you can put it as a standalone function, passing the date as a parameter.
Date.prototype.getISOString = function() {
var zone = '', temp = -this.getTimezoneOffset() / 60 * 100;
if (temp >= 0) zone += "+";
zone += (Math.abs(temp) < 100 ? "00" : (Math.abs(temp) < 1000 ? "0" : "")) + temp;
// "2009-6-4T14:7:32+10:00"
return this.getFullYear() // 2009
+ "-"
+ (this.getMonth() + 1) // 6
+ "-"
+ this.getDate() // 4
+ "T"
+ this.getHours() // 14
+ ":"
+ this.getMinutes() // 7
+ ":"
+ this.getSeconds() // 32
+ zone.substr(0, 3) // +10
+ ":"
+ String(temp).substr(-2) // 00
;
};
If you needed it in UTC time, just replace all the get* functions with getUTC*, eg: getUTCFullYear, getUTCMonth, getUTCHours... and then just add "+00:00" at the end instead of the user's timezone offset.
date = '2012-07-28'; stringdate = new Date(date).toISOString();
ought to work in most newer browsers. it returns 2012-07-28T00:00:00.000Z on Firefox 6.0
My recommendation when working with dates is to parse the date into individual fields from user input. You can use it as a full string, but you are playing with fire.
JavaScript can treat two equal dates in different formats differently.
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/parse
Never do anything like:
new Date('date as text');
Once you have your date parsed into its individual fields from user input, create a date object. Once the date object is created convert it to UTC by adding the time zone offset. I can't stress how important it is to use the offset from the date object due to DST (that's another discussion however to show why).
var year = getFullYear('date as text');
var month = getMonth('date as text');
var dayOfMonth = getDate('date as text');
var date = new Date(year, month, dayOfMonth);
var offsetInMs = ((date.getTimezoneOffset() * 60) // Seconds
* 1000); // Milliseconds
var utcDate = new Date(date.getTime + offsetInMs);
Now you can pass the date to the server in UTC time. Again I would highly recommend against using any date strings. Either pass it to the server broken down to the lowest granularity you need e.g. year, month, day, minute or as a value like milliseconds from the unix epoch.
If you are dealing with dates a lot, it's worth using moment.js (http://momentjs.com). The method to convert to UTC would be:
moment(yourTime).utc()
You can use format to change your date to any format you want:
moment(yourTime).utc().format("YYYY-MM-DD")
There is offset options in moment as well but there is an additional complementary library for dealing with timezone (http://momentjs.com/timezone/). The time conversion would be as simple as this:
moment.tz(yourUTCTime, "America/New_York")
I've found the jQuery Globalization Plugin date parsing to work best. Other methods had cross-browser issues and stuff like date.js had not been updated in quite a while.
You also don't need a datePicker on the page. You can just call something similar to the example given in the docs:
$.parseDate('yy-mm-dd', '2007-01-26');
I just discovered that the 1.2.3 version of Steven Levithan's date.format.js does just what I want. It allows you to supply a format string for a JavaScript date and will convert from local time to UTC. Here's the code I'm using now:
// JavaScript dates don't like hyphens!
var rectifiedDateText = dateText.replace(/-/g, "/");
var d = new Date(rectifiedDateText);
// Using a predefined mask from date.format.js.
var convertedDate = dateFormat(d, 'isoUtcDateTime');
Using moment.js UTC method;
const moment = require('moment');
const utc = moment.utc(new Date(string));
This function works beautifully for me.
function ParseDateForSave(dateValue) {
// create a new date object
var newDate = new Date(parseInt(dateValue.substr(6)));
// return the UTC version of the date
return newDate.toISOString();
}
This method will give you : 2017-08-04T11:15:00.000+04:30 and you can ignore zone variable to simply get 2017-08-04T11:15:00.000.
function getLocalIsoDateTime(dtString) {
if(dtString == "")
return "";
var offset = new Date().getTimezoneOffset();
var localISOTime = (new Date(new Date(dtString) - offset * 60000 /*offset in milliseconds*/)).toISOString().slice(0,-1);
//Next two lines can be removed if zone isn't needed.
var absO = Math.abs(offset);
var zone = (offset < 0 ? "+" : "-") + ("00" + Math.floor(absO / 60)).slice(-2) + ":" + ("00" + (absO % 60)).slice(-2);
return localISOTime + zone;
}
If you need Date Object
Passing only date string Date assumes time to be 00:00 shifted by time zone:
new Date('2019-03-11')
Sun Mar 10 2019 18:00:00 GMT-0600 (Central Standard Time)
If you add current hours and minutes you get proper date:
new Date('2019-03-11 ' + new Date().getHours() + ':' + new Date().getMinutes())
Mon Mar 11 2019 04:36:00 GMT-0600 (Central Standard Time)
The getTimezoneOffset() method returns the time zone difference, in
minutes, from current locale (host system settings) to UTC.
Source: MDN web docs
This means that the offset is positive if the local timezone is behind UTC, and negative if it is ahead. For example, for time zone UTC+02:00, -120 will be returned.
let d = new Date();
console.log(d);
d.setTime(d.getTime() + (d.getTimezoneOffset() * 60000));
console.log(d);
NOTE: This will shift the date object time to UTC±00:00 and not convert its timezone so the date object timezone will still the same but the value will be in UTC±00:00.
This is what I have done in the past:
var utcDateString = new Date(new Date().toUTCString()).toISOString();
For other people whos goal is to get it as a "Date Object" and not as a string, and you only want to display the date/time without the TZ (probably hardcoded), what you can do is:
const now = new Date();
const year = now.getUTCFullYear();
const month = now.getUTCMonth();
const day = now.getUTCDate();
const hour = now.getUTCHours();
const tomorrowUTC= new Date();
tomorrowUTC.setDate(day + 1); // +1 because my logic is to get "tomorrow"
tomorrowUTC.setYear(year);
tomorrowUTC.setMonth(month);
tomorrowUTC.Hours(hour);
// then use the tomorrowUTC for to display/format it
// tomorrowUTC is a "Date" and not a string.
You can then do stuff like:
We will delete your account at ${format(tomorrowUTC, 'EEEE do MMMM hh:mmaaa')} UTC
(format is a date-fns function, you can use other lib if you want);
This is kinda "hacky" as this is still using your local timezone, but if you just wanna display the date and not the timezone, then this works.
If your date has the timezone on it you can use date-fns-tz:
import { zonedTimeToUtc } from 'date-fns-tz';
const dateBrazil = new Date() // I'm in Brazil, you should have or get the user timezone.
const dateUtc = zonedTimeToUtc(dateBrazil, 'America/Sao_Paulo')
Looking at your question its clear that you just want to send the date range to your backend for further post processing.
I am assuming you are conforming to the standard data guidelines which expect the data to be in a particular format. For example, I use ODATA which is a RESTfull API which expects date time objects to be in the format:-
YYYY-MM-DDT00:00:00.
That can be easily achieved via the snippet posted below(Please change the format as per your requirement).
var mydate;//assuming this is my date object which I want to expose
var UTCDateStr = mydate.getUTCFullYear() + "-" + mydate.getUTCMonth() + "-" + mydate.getUTCDate() + "T00:00:00";
If on the other hand, you are in my situation wherein you have received a date from your backend, and the browser converts that to your local date. You on the other hand are interested in the UTC date then you can perform the following:-
var mydate;//assuming this is my date object which I want to expose
var UTCDate = new Date(mydate);/*create a copy of your date object. Only needed if you for some reason need the original local date*/
UTCDate.setTime(UTCDate.getTime() + UTCDate.getTimezoneOffset() * 60 * 1000);
The code snippet above basically adds/subtracts the time added/subtracted by the browser based on the timezone.
For example if I am in EST(GMT-5) and my Service returns a date time object = Wed Aug 17 2016 00:00:00 GMT-0500
my browser automatically subtracts the timezone offset(5hrs) to get my local time. So if I try to fetch the time I get Wed Aug 16 2016 19:00:00 GMT-0500. This causes a lot of problems. There are a lot of libraries out there which will definitely make this easier but I wanted to share the pure JS approach.
For more info please have a look at: http://praveenlobo.com/blog/how-to-convert-javascript-local-date-to-utc-and-utc-to-local-date/ where in I got my inspiration.
Hope this helps!
var userdate = new Date("2009-1-1T8:00:00Z");
var timezone = userdate.getTimezoneOffset();
var serverdate = new Date(userdate.setMinutes(userdate.getMinutes()+parseInt(timezone)));
This will give you the proper UTC Date and Time.
It's because the getTimezoneOffset() will give you the timezone difference in minutes.
I recommend you that not to use toISOString() because the output will be in the string Hence in future you will not able to manipulate the date
Using moment package, you can easily convert a date string of UTC to a new Date object:
const moment = require('moment');
let b = new Date(moment.utc('2014-02-20 00:00:00.000000'));
let utc = b.toUTCString();
b.getTime();
This specially helps when your server do not support timezone and you want to store UTC date always in server and get it back as a new Date object. Above code worked for my requirement of similar issue that this thread is for. Sharing here so that it can help others. I do not see exactly above solution in any answer. Thanks.
I know this question is old, but was looking at this same issue, and one option would be to send date.valueOf() to the server instead. the valueOf() function of the javascript Date sends the number of milliseconds since midnight January 1, 1970 UTC.
valueOf()
You can use the following method to convert any js date to UTC:
let date = new Date(YOUR_DATE).toISOString()
// It would give the date in format "2020-06-16T12:30:00.000Z" where Part before T is date in YYYY-MM-DD format, part after T is time in format HH:MM:SS and Z stands for UTC - Zero hour offset
By far the best way I found to get the GMT time is first get your local date time. Then convert in to GMT String. Then use the string to build new time by removing the timezone.
let dtLocal = new Date()
let dt = new Date(dtLocal.toISOString().split('Z')[0])
Note: - it will create the new datetime in GMT. But it will be local date time as timezone will be attached to it.
Extension function:
if (!Date.prototype.toUTC){
Date.prototype.toUTC = function(){
var utcOffset = new Date().getTimezoneOffset();
var utcNow = new Date().addMinutes(utcOffset);
return utcNow;
};
}
Usage:
new Date().toUTC();
I need to convert datetimes from an input format which I can't change (this: "Tue, 30 Jul 2019 21:15:53 GMT") to UTC, in Javascript.
I actually need to get these dates as the number of milliseconds since the Unix epoch (1970) but getting in UTC would be a start.
Is there a way to do this easily? I can use a 3rd party library if needed. I've heard of moment-timezone.js but not clear how to parse the 3 letter timezone, i.e. these: https://en.wikipedia.org/wiki/List_of_time_zone_abbreviations.
The correct solution is a library that maps these abbreviations to offsets from GMT. Neither moment-timezone, nor date-fns-tz, nor luxon, nor timezone-support do this, but timezone-abbr-offsets does and is very minimalistic.
Fortunately, new Date() can parse your format minus the timezone, so we'll split that away and calculate the offset back:
import timezones from 'timezone-abbr-offsets';
function abbrTzToUtc(dateString) {
// Get the date and the timezone from the input string
let [, date, tz] = dateString.match(/^(.*)\s+(\w+)$/);
// Ignore the timezone and parse the date as GMT
date = new Date(date + 'Z');
// Add the offset caused by the original timezone
date = new Date(date.getTime() + timezones[tz] * 60 * 1000);
return date;
}
console.log(abbrTzToUtc('Tue, 30 Jul 2019 21:15:53 MET'));
As a test, the code above should return 2019-07-30T22:15:53.000Z.
If you want number of milliseconds since the Unix epoch, return date.getTime() instead.
If you want to convert the date into UTC format you can use toISOString()
new Date('Tue, 30 Jul 2019 21:15:53 GMT').toISOString()
For more info please check this reference
Moreover, to convert the date into milliseconds you can use Date.UTC()
Date.UTC(year[, month[, day[, hour[, minute[, second[, millisecond]]]]]])
reference
Example:
utcMillisecond = (e) => {
const regex = /(T)|(:)|(-)/g;
const utc = new Date(e).toISOString().slice(0, 19).replace(regex, ' ').split(' ');
const utcMillisecond = Date.UTC(utc[0], utc[1], utc[2], utc[3], utc[4])
return utcMillisecond
}
utcMillisecond("Tue, 30 Jul 2019 21:15:53 GMT")
//1567199700000
const dt = new Date('2017-12-12');
console.log(format(dt, 'YYYY-MM-DD'));
The above code logs 2017-12-11 in the US, but 2017-12-12 in India.
I followed this github thread here and tried out things but am not getting the desired results.
My expectation is to print the same date irrespective of time zone
Why I need this :
Consider a scenario involving birthdates. If i am giving some input date, it has to be displayed as same date in all regions irrespective of their timezones.
You will need to subtract the time zone offset of your local time zone from the Date instance, before you pass it to format from date-fns. For example:
const dt = new Date('2017-12-12');
const dtDateOnly = new Date(dt.valueOf() + dt.getTimezoneOffset() * 60 * 1000);
console.log(format(dtDateOnly, 'YYYY-MM-DD')); // Always "2017-12-12"
Problem
You want to handle only the date part of the Date instance, because the time part does not make sense for birthdates. However, the Date object does not offer any "date-only" mode. You can access both its date and time parts in the local time zone or UTC. The problem is, that format from date-fns prints the output always in the local time zone.
When you executed the constructor only with the date part:
const dt = new Date('2017-12-12');
The JavaScript engine actually assumed a string in the incomplete ISO 8601 format and perfomed this:
const dt = new Date('2017-12-12T00:00:00.000Z');
It may still look "harmless" to you, but the date instance exposes the value not only in UTC, but also in the local time zone. If you construct the Date instance on the East Coast of the US, you will see the following output:
> const dt = new Date('2017-12-12');
> dt.toISOString()
'2017-12-12T00:00:00.000Z'
> dt.toString()
'Tue Dec 11 2017 19:00:00 GMT-0500 (EST)'
> d.toLocaleString()
'12/11/2017 7:00:00 PM'
Solution
If you know, that format from date-fns reads date and time parts from the date instance in the local time zone, you will need to make your date "looking like" the midnight in your local time zone and not in UTC, which you passed to the Date constructor. Then you will see the year, month and date numbers preserved. It means, that you need to subtract the time zone offset of your local time zone for the specified day. Date.prototype.getTimezoneOffset returns the offset, but with an inverted sign and in minutes.
const dt = new Date('2017-12-12');
// Tue Dec 11 2017 19:00:00 GMT-0500 (EST)
const dtDateOnly = new Date(dt.valueOf() + dt.getTimezoneOffset() * 60 * 1000);
// Tue Dec 12 2017 00:00:00 GMT-0500 (EST)
console.log(format(dtDateOnly, 'YYYY-MM-DD'));
// Prints always "2017-12-12", regardless the time zone it executed in
However, such Date instance can be used only to format the date-only value. You cannot use it for computing date differences, for example, which would need the original and correct UTC value.
Alternative
If you need always the same date-only format and not the format specific to the current locale, you do not need date-fns. You can format the string by the concatenation of padded numbers:
const dt = new Date('2017-12-12');
const year = dt.getUTCFullYear()
const month = dt.getUTCMonth() + 1 // Date provides month index; not month number
const day = dt.getUTCDate()
// Print always "2017-12-12", regardless the time zone it executed in
console.log(year + '-' + padToTwo(month) + '-', padToTwo(day));
// Or use a template literal
console.log(`${year}-${padToTwo(month)}-${padToTwo(day)}`);
function padToTwo (number) {
return number > 9 ? number : '0' + number
}
Only adding the #ferdinand-prantl answer. If you are using the date-fns, you can parse the string date ('2017-12-12') using the parseISO(here) fn from date-fns, which will complete the missing ISO 8601 format with your local time zone. When you use the format fn, you are going to keep the date.
const strDate = '2017-12-12';
const isoDate = parseISO(strDate);
const formattedDate = format(isoDate, 'YYYY-MM-DD');
console.log({strDate, isoDate, formattedDate})
//{
// strDate: '2017-12-12',
// isoDate: 2017-12-12T02:00:00.000Z,
// formattedDate: '2017-12-12'
//}
I need a js Date object with specified values for date and year. I would expect
new Date("2000-01-01") to give me Date object with 2000 as value for getFullYear(), but if my computer's time settings are set to Chicago timezone, I'm getting Fri Dec 31 1999 18:00:00 GMT-0600 (CST), and for Buenos Aires: Fri Dec 31 1999 22:00:00 GMT-0200 (ARST).
Is there a way to create Date object, with .getFullYear() returning the date we set in constructor, no matter what timezone is set on user's machine?
Update:
I need this Date object to be used in another library (which calls its .getFullYear() method, so using UTC getters doesn't really help.
When parsing a string to a Date in JavaScript, a value that is in YYYY-MM-DD format is interpreted as a UTC value, rather than a local-time value.
The key is that the parts are separated by hyphens, and that there is no time zone information in the string. The ECMAScript 5.1 Spec says in §15.9.1.15:
... The value of an absent time zone offset is “Z”.
That means, if you don't specify an offset, it will assume you meant UTC.
Note that since this is the opposite of what ISO-8601 says, this is behavior has been changed in ECMAScript 2015 (6.0), which says in §20.3.1.16:
... If the time zone offset is absent, the date-time is interpreted as a local time.
Therefore, when this provision of ES6 is implemented properly, string values of this format that used to be interpreted as UTC will be interpreted as local time instead. I've blogged about this here.
The workaround is simple. Replace the hyphens with slashes:
var s = "2000-01-01";
var dt = new Date(s.replace(/-/g, '/'));
Another workaround that is acceptable is to assign a time of noon instead of midnight to the date. This will be parsed as local time, and is far enough away to avoid any DST conflicts.
var s = "2000-01-01";
var dt = new Date(s + "T12:00:00");
Alternatively, consider a library like moment.js which is much more sensible.
var s = "2000-01-01";
var dt = moment(s, 'YYYY-MM-DD').toDate();
You can write new method to 'Date.prototype', and use it to get date which will be including the local timezone offset.
//return the date with depend of Local Time Zone
Date.prototype.getUTCLocalDate = function () {
var target = new Date(this.valueOf());
var offset = target.getTimezoneOffset();
var Y = target.getUTCFullYear();
var M = target.getUTCMonth();
var D = target.getUTCDate();
var h = target.getUTCHours();
var m = target.getUTCMinutes();
var s = target.getUTCSeconds();
return new Date(Date.UTC(Y, M, D, h, m + offset, s));
};
Here is a little trick that may help someone:
let date = new Date();
console.log(date); // -> Fri May 28 2021 01:04:26 GMT+0200 (Central European Summer Time)
const tzOffsetMin = Math.abs(date.getTimezoneOffset()) // the minutes of the offset timezone
const tzOffsetHour = tzOffsetMin / 60; // timezone offset in hour
console.log(tzOffsetHour); // -> 2
date.setHours(date.getHours() + tzOffsetHour); // sum to date hour the timezoneoffset
const isovalue = date.toISOString();
console.log(isovalue); // -> 2021-05-28T01:04:26.156Z
In this way you "bypass" the timezone offset wherever you are
I'm creating dates like this:
var StartDate = new Date(data.feed.entry[i].gd$when[j].startTime);
When a date string is received specifying date and time in the form:
"2014-04-12T20:00:00.000-05:00"
Date() interprets this perfectly fine returning:
Sat Apr 12 2014 19:00:00 GMT-0500 (CDT)
However, when the date string is received with no time information in the form:
"2014-04-07"
then Date() is interpreting it as:
Sat Apr 05 2014 19:00:00 GMT-0500 (CDT)
Looks like Date() is taking the -07 as the time and I have no clue where is it getting the date as 05. Any idea what might be the problem?
Could it be, somehow, Date() is interpreting a different time zone because in the first string the time zone is determined at the very end but in the "all day" event there is no indication of the time zone.
Has anybody found this issue? If yes, how did you solve it?
UPDATE: After researching a little bit more this parsing issue I noticed something very weird:
The following statement:
new Date("2014-4-07")
would return Mon Apr 07 2014 00:00:00 GMT-0500 (CDT) which is correct, but the following one:
new Date("2014-04-07")
returns Sun Apr 06 2014 19:00:00 GMT-0500 (CDT) which is the wrong one. So, for whatever reason, seems like the padding zeros affect the way the date is parsed!
You're using the Date() function wrong.
It only accepts parameters in the following formats.
//No parameters
var today = new Date();
//Date and time, no time-zone
var birthday = new Date("December 17, 1995 03:24:00");
//Date and time, no time-zone
var birthday = new Date("1995-12-17T03:24:00");
//Only date as integer values
var birthday = new Date(1995,11,17);
//Date and time as integer values, no time-zone
var birthday = new Date(1995,11,17,3,24,0);
Source: MDN.
The Date() function does not accept timezone as a parameter. The reason why you think the time-zone parameter works is because its showing the same time-zone that you entered, but that's because you're in the same time-zone.
The reason why you get Sat Apr 05 2014 19:00:00 GMT-0500 (CDT) as your output for Date("2014-04-07" ) is simply because you used it in a different way.
new Date(parameters) will give the output according to the parameters passed in it.
Date(parameters) will give the output as the current date and time no matter what parameter you pass in it.
Prior to ES5, parsing of date strings was entirely implementation dependent. ES5 specifies a version of ISO 8601 that is supported by may browsers, but not all. The specified format only supports the Z timezone (UTC) and assumes UTC if the timezone is missing. Support where the timezone is missing is inconsistent, some implementations will treat the string as UTC and some as local.
To be certain, you should parse the string yourself, e.g.
/* Parse an ISO string with or without an offset
** e.g. '2014-04-02T20:00:00-0600'
** '2014-04-02T20:00:00Z'
**
** Allows decimal seconds if supplied
** e.g. '2014-04-02T20:00:00.123-0600'
**
** If no offset is supplied (or it's Z), treat as UTC (per ECMA-262)
**
** If date only, e.g. '2014-04-02', treat as UTC date (per ECMA-262)
*/
function parseISOString(s) {
var t = s.split(/\D+/g);
var hasOffset = /\d{2}[-+]\d{4}$/.test(s);
// Whether decimal seconds are present changes the offset field and ms value
var hasDecimalSeconds = /T\d{2}:\d{2}:\d{2}\.\d+/i.test(s);
var offset = hasDecimalSeconds? t[7] : t[6];
var ms = hasDecimalSeconds? t[6] : 0;
var offMin, offSign, min;
// If there's an offset, apply it to minutes to get a UTC time value
if (hasOffset) {
offMin = 60 * offset / 100 + offset % 100;
offSign = /-\d{4}$/.test(s)? -1 : 1;
}
min = hasOffset? +t[4] - offMin * offSign : (t[4] || 0);
// Return a date object based on UTC values
return new Date(Date.UTC(t[0], --t[1], t[2], t[3]||0, min, t[5]||0, ms));
}
An ISO 8601 date string should be treated as UTC (per ECMA-262), so if you are UTC-0500, then:
new Date('2014-04-07'); // 2014-04-06T19:00:00-0500
The behaviour described in the OP shows the host is not compliant with ECMA-262. Further encouragement to parse the string yourself. If you want the date to be treated as local, then:
// Expect string in ISO 8601 format
// Offset is ignored, Date is created as local time
function parseLocalISODate(s) {
s = s.split(/\D+/g);
return new Date(s[0], --s[1], s[2],0,0,0,0);
}
In your function you can do something like:
var ds = data.feed.entry[i].gd$when[j].startTime;
var startDate = ds.length == 10? parseLocalISODate(ds) : parseISOString(ds);
Also note that variables starting with a capital letter are, by convention, reserved for constructors, hence startDate, not StartDate.
(I would add a comment but i don't have 50 rep yet)
See what
new Date().getTimezoneOffset()
returns, I would expect a big negative value, that would be the only reasonable explanation to your problem.
I have had some trouble with date conversions in the past, in particular with daytime saving timezones, and as work around i always set the time explicitly to midday (12:00am). Since I think you were using knockout, you could just make a computed observable that appends a "T20:00:00.000-05:00" or the appropiate time zone to all "day only" dates