Firebase Timestamp returns with wrong date - Javascript - javascript

I'm trying to get the Timestamp value from firestore (using Firebase Functions), and I´ve successfully done it localy with the toDate() method of Timestamp, and moment library.
moment(doc.data().EndDate.toDate())
But when I deploy my code to firebase and test the function, somehow the toDate() returns a Date with 1 less hour than the saved timestamp on firebase. I suppose it is transforming my date to UTC, since I'm in UTC+1, and the Timestamp is also stored with UTC+1 in firestore, but I don't know how to reliably get the timestamp date as is in firestore, regardless of timezones.
If someone knows why this happens or has any idea how to solve it it would be great.

All timestamps in Firestore are stored in UTC. If you see something different in the Firebase console, that's just your browser formatting it for your local timezone.
In JavaScript, all Date objects are also represented in UTC. If you format that as a string, you will again possibly get a different representation based on your local timezone.
If you write code that computes values using dates or timestamps, you should perform all your computations using UTC. This is the pretty much all computing systems want to deal with dates. When it comes time to format the date for display to an end user, only then should you take timezone into account, and present something according to the user's preferences.

Related

Firebase toDate() use CEST instead of localTime

I am using firebase toDate()-method to get a Date object from my timestamp:
myTimestamp.toDate()
This creates a Date-object (which I need), but in local time (the time my operating system uses). How can I get it to give me a Date-Object in CEST/CET?
edit:
The timestamp comes from firebase and I am using their toDate() method.
The integer value contained by a Date object (milliseconds since unix epoch) is not affected by timezones. It represents the same point in time for all people on the planet.
However, when you print a Date object, you will see the date rendered with local timezone. If you want just that integer number inside the Date, call getTime() on it for use elsewhere.
You can feed a Date (or the underlying number) to other libraries that may do what you really want with the date, including momentjs with moment-timezone. For example, this may work with moment:
moment(your_date).tz('Desired Timezone').format('ha z')

Dealing with js localized date in C#

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.

Passing a time zone into a web api call from moment with nodatime

I'm about to go insane dealing with datetime issues and the web.
I have a web server hosted in the Central Time Zone. When clients in the Eastern Time Zone try and schedule an item for a given day using my app, they pass in the value of (for example) 3/14/2015. When we pass the code back to our model, which is sent to the web api, we persist is using something like the code below.
moment.utc($("#mydatepicker").val).hour(0).minute(0).second(0)).toISOString();
This results in a string like the following:
2015-03-14T04:00:00.000Z
When the item is converted back on the server in web api, it converts to
3/13/2015 11:00:00 PM
Logic then strips off time and you can see what happens from here. Since I stripped off the time, it is now the day prior and that is the value persisted to the database.
I need to know some way to send a value from moment, into the web api preferrably as a ZonedDateTime in the client's time zone. I can then convert it to UTC for persistance in the DB.
I've seen things about using NodaTime.Serialization.JsonNet, but I am unclear on how to to use it with Moment and pass it back and forth across web api/ajax.
I need to know some way to send a value from moment, into the web api preferrably as a ZonedDateTime in the client's time zone. I can then convert it to UTC for persistance in the DB.
If that's what you want, then:
In your moment.js code, use .format() instead of .toISOString(), which will still give you an ISO8601 string, but will include the local offset instead of setting it to UTC.
In your ASP.Net code, define your values as a DateTimeOffset (or a noda OffsetDateTime) rather than a DateTime.
However, I don't think that's really what you want. When it comes to dates and times, context is super important. Here, you said you were picking a date from a date picker. When you do that - what time is being chosen by the user? In most cases, they aren't choosing a time - they're just picking a date. But since the JavaScript Date object is really a "date + time" object, it assigns midnight as a default time. Moment is no better in this regard.
Really, converting to UTC doesn't make logical sense when you are just talking about a calendar date. The string value you probably should be sending across the wire should just be a whole date, as in "2015-03-14". My guess is that is what you are starting with anyway. If not, then do moment.utc(yourvalue).format("YYYY-MM-DD") to get it. (Using UTC here is just a way to avoid local time zone issues, like midnight not existing in Brazil on the spring-forward day.)
This corresponds to the NodaTime LocalDate type in your .NET code. If you weren't using Noda Time, you would define the type as a DateTime and just ignore the time portion. In your database, if there's a date-only type available, then use it. For example, SQL Server has a date type.
I'd also encourage you to watch my Pluralsight course, Date and Time Fundamentals - which covers many of these issues.
Regarding using NodaTime.Serialization.JsonNet in WebAPI (so you can use LocalDate directly), in your WebApiConfig.cs file, wire it up like so:
config.Formatters.JsonFormatter.SerializerSettings
.ConfigureForNodaTime(DateTimeZoneProviders.Tzdb);
Then it should just work.
I would start by sending all dates and times to the server as UTC times. If you store UTC times only then you should be able to show the correct time that something is scheduled on the client side.
When you create your moment on the client side, do you run it out .toDate() first before sending it to the server side? What code are you running on the server side? Is it a .Net WebApi?

how to handle DST and timezones in JavaScript

What is the best approach for dealing with DST values when your web service accepts requests from different timezones than that of your server?
My webservice accepts date strings using the ISO8601 standard (2012-02-21T05:00:00.000-05:00)
I want to account for DST but don't want the overhead of maintaining or connecting to a database to get the DST for each request which comes in from a different timezone to my server.
One approach im considering is using the servers default DST settings and then for each request that comes in convert it to the same timezone as my server is in. Then when the processing is done , convert the string back to the timezone of the client and return. The conversion of the response data could be done on the server or the client.
Any suggestions?
You could also take a look at the XDate project for handling date objects in Javascript. It's quite similar to JodaTime (in Java). Very easy to use and semantic.
XDate project
Here's what I would do. Before you submit your data/time, parse the strings into a JavaScript Date object. Then call getTime() and submit that value. getTime() returns the number of milliseconds since the UTC epoch, so in effect, it normalizes your times. Then when you return data to the user, pass in your UTC millisecond value to the constructor of a Date object and display the time as you would. By default, it'll display in the user's timezone.

Date format in mongodb/mongoose

When I create a date in javascript it is in zulu, when I save it in my mongodb via mongoose it is transformed to UTC (its keeps the same time value, but the timezone is changed). I'd like it to stay in zulu when saved, how can I set this option in mongoose ?
thanks
MongoDB stores all DateTimes in UTC. Any local times you supply are converted to UTC when stored in the database. The recommended approach is to always convert DateTime values to UTC yourself before storing them in the database, that way you are in full control.
Resources:
https://jira.mongodb.org/browse/CSHARP-185
Dealing with how MongoDB stores DateTime when used with Service Locator Pattern

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