How to convert Javascript datetime to C# datetime?

Question

I have been reading that if you want to convert from JavaScript dates to C# dates you should use getTime() and then add that result to a C# DateTime.

Suppose I have this JavaScript time:

Date {Tue Jul 12 2011 16:00:00 GMT-0700 (Pacific Daylight Time)}

It renders to 1310522400000 milliseconds

var a = new DateTime(1970, 01, 01).AddMilliseconds(1310522400000);

// result
7/13/2011 2:00:00 AM

So this is wrong. I am not sure what I need to do.

Answer 1

You could use the toJSON() JavaScript method, it converts a JavaScript DateTime to what C# can recognise as a DateTime.

The JavaScript code looks like this

var date = new Date();
date.toJSON(); // this is the JavaScript date as a c# DateTime

Note: The result will be in UTC time

Answer 2

First create a string in your required format using the following functions in JavaScript

var date = new Date();
var day = date.getDate();       // yields date
var month = date.getMonth() + 1;    // yields month (add one as '.getMonth()' is zero indexed)
var year = date.getFullYear();  // yields year
var hour = date.getHours();     // yields hours 
var minute = date.getMinutes(); // yields minutes
var second = date.getSeconds(); // yields seconds

// After this construct a string with the above results as below
var time = day + "/" + month + "/" + year + " " + hour + ':' + minute + ':' + second; 

Pass this string to codebehind function and accept it as a string parameter.Use the DateTime.ParseExact() in codebehind to convert this string to DateTime as follows,

DateTime.ParseExact(YourString, "dd/MM/yyyy HH:mm:ss", CultureInfo.InvariantCulture);

Hope this helps...

Answer 3

You were almost right, there's just need one little fix to be made:

var a = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)
    .AddMilliseconds(1310522400000)
    .ToLocalTime();

Answer 4

If you want to send dates to C# from JS that is actually quite simple - if sending UTC dates is acceptable.

var date = new Date("Tue Jul 12 2011 16:00:00 GMT-0700");
var dateStrToSendToServer = date.toISOString();

... send to C# side ...

var success = DateTimeOffset.TryParse(jsISOStr, CultureInfo.InvariantCulture, DateTimeStyles.AssumeUniversal, out var result);

C# DateTime already understands ISO date formats and will parse it just fine.

To format from C# to JS just use DateTime.UtcNow.ToString("o").

Personally, I'm never comfortable relying on math and logic between different environments to get the milliseconds/ticks to show the EXACT same date and time a user may see on the client (especially where it matters). I would do the same when transferring currency as well (use strings instead to be safe, or separate dollars and cents between two different integers). Sending the date/time as separate values would be just a good (see accepted answer).