I am using new Date(<date-string>) and then .getTime() to pass date strings to milliseconds from 1970.
The problem is that the date strings does not contain the timezone on them. They are British, so the timezone will be GMT or GMT+1 depending on the date...
When I use this technique in the front-end (Chrome), or in the back-end (Node.js). The time zone taken is the British one (GMT or GMT+1 depending on the date). I assume that is taken from the OS.
However, when using a Node.js server which I have been told is configured to be in UTC... the timezone is always going to be GMT, leading to errors during the British Summer Time.
Is there any way to tell Date to take the timezone from the OS without changing the server configuration?
Example:
var aDate = new Date('2016-06-23 10:15:0');
var timestamp = aDate.getTime();
Just in case my explanation is not clear:
// Executed on 28-06-2016
// In the browser (in London)
new Date().getTimezoneOffset(); // -60
new Date('28-06-2016 11:11:11').getTimezoneOffset(); // -60
new Date('28-01-2016 11:11:11').getTimezoneOffset(); // 0
// In the Node.js server I am forced to use, which is configured to use UTC
new Date().getTimezoneOffset(); // 0
new Date('28-06-2016 11:11:11').getTimezoneOffset(); // 0
new Date('28-01-2016 11:11:11').getTimezoneOffset(); // 0
// Ideally, I would like to have the output I get in the browser when I run the code in the UTC Node.js server
I recommend using Moment Timezone for this, since this would be needlessly complicated to implement without a library. To get UTC in milliseconds from a given date in a given timezone, you can do this:
const moment = require('moment-timezone');
function londonTimeToUTC(dateString) {
return moment.tz(dateString, 'DD-MM-YYYY HH:mm:ss', 'Europe/London').valueOf();
}
console.log(londonTimeToUTC('28-06-2016 11:11:11')); // 1467108671000
console.log(londonTimeToUTC('28-01-2016 11:11:11')); // 1453979471000
The second argument passed to moment.tz() is a format string, which is necessary if the date string is not in ISO format. The third argument is any valid timezone identifier.
Is there any way to tell Date to take the timezone from the OS without changing the server configuration?
The time zone from the OS is what the Date object uses. If you're asking if you can change that time zone without changing the configuration, then no - there is not a way to do that. The Date object always takes on the behavior of the local time zone. Even if you supply an offset in the input string, it just uses that to determine the internal UTC timestamp. Output via most of the properties (including toString and getTimezoneOffset) will always use the local time zone.
Even in your examples, you cannot count on the browser behavior always returning the values you showed, simply because each user visiting your web site may have a different time zone setting.
The recommended way to deal with this is by using the moment.js library, which can handle UTC and local time by itself, but may require use of the moment-timezone extension if you are wanting to work with a specific time zone, such as Europe/London.
Now, with that said, if you're certain that your entire node.js application will run in a single time zone, and you're running on Linux or OSX (not Windows), then you can indeed change which time zone that node.js considers to be "local". Simply set the TZ environment variable before you launch node, like this:
env TZ='Europe/London' node server.js
There is no equivalent for the browser, or for Windows. And you still have to contend with possible non-UK users on your web site - so this doesn't guaranteed a match between client and server time. But it does address your question.
See also:
How to initialize javascript date to a particular timezone
How to make the timezone of date to UTC
How to set default timezone in Node.js
Related
is it possible to convert a UTC date coming from a server to a specific (UK) timezone using JavaScript? This is for the case where users may have the incorrect local timezone configured.
You can specify a time zone in the options passed to toLocaleString, which will use the point-in-time represented by the Date object to create a localized string that is converted to the specified time zone.
For example:
new Date("2020-09-17T17:15:00.000Z").toLocaleString('en-GB', { timeZone: 'Europe/London' })
//=> "17/09/2020, 18:15:00"
Note the first parameter is the locale for the format, not the time zone. If you don't want a specific format, you can pass undefined instead - which will use the user's active locale settings to choose the format.
Note also that you can not get a Date object that is in that time zone. The Date object only stores a point in time (as a Unix timestamp with millisecond precision), and it always uses the computer's local time zone setting for its functions that need local time conversions (except as show above).
(The TC39 Temporal proposal is working to improve this.)
I want to display the local date of the user, but nothing is working for me. It always returns the UTC time.
I have tried:
This returns UTC - also in here offset comes as zero.
let visitDate = moment.utc().format();
let offset = moment().utcOffset();
let visitDate1 = moment.utc(visitDate).utcOffset(offset)
This returns UTC
let visitDate = new Date()
let visitDate1 = moment(visitDate).local().format('MM-DD-YYYY hh:mm:ss');
This returns UTC
let visitDate = new Date()
let visitDate1 = visitDate.toLocaleDateString()
I have tried several methods, but it doesn't matter what I do, I always get UTC time. If I try on localhost then it displays the correct time, but once I host the page it displays UTC.
How can I transform to local?
moment().local() uses the timezone of the local machine, that's why it works in localhost
if you know it, I would specify the timezone:
moment.tz("America/Los_Angeles").format()
There seem to be several possible points of failure. I'll list the ones I think of below, and you can assess whether they're relevant to your setup.
1) The code that manipulates the date is executed on the server, not locally
Most of our Javascript code is written to execute in the user's browser, so that's the default assumption. If that assumption is wrong in this case, and the code is being executed on the server, then "local" means "on the server." Your server should be running with UTC time, which could produce the results you're seeing.
2) The user is running a browser set to UTC
If the browser you're using for testing is set to consider UTC as local time, it'd produce the results you're seeing. Since you're probably using the same machine for localhost and for testing, it's an unlikely source of the problem...but worth noting nonetheless.
3) Changing how the date is displayed does not change how the date is stored
Many of the tools we have for setting/changing the time zone affect how the date is displayed. However, Date objects in Javascript are stored using Unix Time (in milliseconds), which is UTC. When you create a Date object--even with a time zone specified--the behind-the-scenes representation will still be an integer (representing a number of milliseconds) and based on UTC. If you're checking the stored value rather than the displayed value, when you're testing, then there's a good chance you'll always see UTC. However, the work you're doing with the moment library should have the date formatted correctly. If you're checking the moment object, you should be seeing the time zone you expect to see.
If none of these three possible failure points applies to your context, then perhaps they spark an idea for you. (The third one, especially, feels like it might be on the right track even if it's not what's happening in your case.)
My app (back-end in C# & front-end in Angular Materials) has a search screen allowing user to specify the date period using datepickers. The problem is that some of the users are not in UK while all the data they view has been created with GMT date. So if someone in Germany selects date 01/01/2017 in datepicker, my back-end reads it as 31/12/2016 23:00:00 resulting in incorrect search results.
Can someone advise me how to deal with this? I'd like to still use the Angular Material datepicker but be sure that I'm passing the date selected by the user. I know I can transform the date before posting it like this:
moment(myDate).format('MM/DD/YYYY'))
but I have a lot of cases like this and would prefer some generic solution.
For transmission and storage, I advise using UTC for everything. Only at the point of display should the time be converted to whatever locale the user has selected. Despite this being an old problem, running into time conversion issues is still quite common. Most places I've worked at will store everything as UTC timestamps or Unix epoch time with respect to UTC, that way there is no question what the meaning is anywhere in the system. If/when it needs to be rendered to something local, we do it on the client side.
For example, to get the local time converted to UTC as a string:
var noTimeZone = new Date().toUTCString();
-or-
var noTimeZone = new Date().toISOString();
Or, if you want a numeric value so you don't have to deal with funky format parsing between client/server, you can get the Unix epoch:
var unixEpochMS = new Date().getTime();
Mind you, Date.getTime() will return milliseconds rather than seconds. Also note that the Unix epoch is defined in terms of UTC. That is, any numeric value that is a timestamp is expected to be UTC. If you want a different timezone, you need to parse the value and then set the timezone to what you want.
Solution 1:
I think the solution is to get your user's timezone. You can use Javascript to get timezone from user's computer and send it to server with the request.
var d = new Date();
var tz = d.getTimezoneOffset()/-60;
tz will be 2 if user's timezone is GM+2
Soution 2:
You send and receive Unix timestamp. But then you need to convert the timestamp to readable date/time based on user's timezone.
I am working on a platform that has users from all over the world, but certain settings are bound to a predefined timezone datetime.
What does this mean? If a user connects from a different timezone the app should still show him the current time in the predefined timezone regardles from where he logs in. I need to calculate this on the client side with javascript with only the timezone string.
What I would like to do is something like this:
new TimezoneDate('timezone');
and the result should be the current datetime for that timezone.
I know there are JS libs that handle this but I am asking if there is a simple JS solution without using external libs?
Depends on your definition of simple; but not really. Javascript does not have support for timezones out of the box. I would highly recommend Moment Timezone http://momentjs.com/timezone/ since it is very user friendly. I am also in the middle of a project with the same requirements and this library has made my work a lot easier.
Edit:
With the library, doing what you want is as easy as:
var timezonedDate = moment.tz('YOUR TZ STRING').toDate();
You can try:
var offset = new Date().getTimezoneOffset();
Or to get the difference in hours:
var x = new Date();
var currentTimeZoneOffsetInHours = x.getTimezoneOffset() / 60;
Mozilla Reference
The time-zone offset is the difference, in minutes, between UTC and
local time. Note that this means that the offset is positive if the
local timezone is behind UTC and negative if it is ahead. For example,
if your time zone is UTC+10 (Australian Eastern Standard Time), -600
will be returned. Daylight saving time prevents this value from being
a constant even for a given locale.
My app runs on Linux servers, where the time is (naturally) set to UTC/GMT. However the app is developed on Mac desktops where the time is typically set to a local timezone.
I could change every new Date() in my code to run:
var date = new Date().getTime();
And thus ensure dates on the server are always GMT, but that seems inelegant.
I understand previous versions of node used to always return UTC/GMT. Is there any way to bring this behavior back?
Edit: Removed adding timezone offset to getTime() per comments - since getTime() is already in UTC.
You can use TZ configuration parameter of node.js as follows.
For bash (and related)
export TZ=UTC
For Powershell
$env:TC = 'UTC'
Then for both:
nodejs server/index.js
From the MDN docs on Date#getTime:
The value returned by the getTime method is the number of milliseconds since 1 January 1970 00:00:00 UTC.
Assuming you're storing dates/times as numbers (which I would recommend), getTime is already UTC, always.
Suppose your client then requests a date from the server. If the server provides the date as a number, the client can then do:
new Date(timestamp);
And it will be correctly adjusted to the local time on the client.
Of course, maybe I'm misunderstanding your problem. But I just want to point out that this...
new Date().getTime() + new Date().getTimezoneOffset();
...should never really make sense. It's taking a UTC-based time and then offsetting it further, in essence double-offsetting a time.