How do I get javascript's Date.parse() in .Net?

Question

I'm using .NET to generate a JSON file that has many Dates in it.

For compression, I want to store them as milliseconds since Jan 1, 1970 and not strings, then convert them to Javascript Dates. But .Net's idea of milliseconds since 1970-01-01 don't match Javascript:

Javascript:

Date.parse("2012-05-15T13:57:57.0000000+00:00")
1337090277000

VB.Net:

Date.Parse("2012-05-15T13:57:57.0000000+00:00").Subtract(New Date(1970,1,1)).TotalMilliseconds
1337101077000.0

The difference is 10800 seconds. The difference at 1970-01-01 is 0 and changes over time.

Is there a way to compute Javascript's idea of milliseconds-since-epoch from within .Net?

The difference is 3 hours exactly. Perhaps the original time was from a different time zone? — JConstantine
– JConstantine, Commented Jul 28, 2012 at 13:09

Esailija · Accepted Answer · 2012-07-28 15:16:26Z

4

You are comparing apples to oranges.

This is exactly what you would get in javascript as well when in UTC+3 (Israel):

Date.parse("2012-05-15T13:57:57.0000000+00:00") - new Date(1970,1,1)
//1334419077000

This is because when you do new Date in javascript, that's according to the machine's timezone. It looks like it's the same for vb.net.

You would get the correct number in javascript with:

Date.parse("2012-05-15T13:57:57.0000000+00:00") - Date.UTC(1970,1,1)
//1334411877000

In VB.net

    Dim a As Date
    a = Date.Parse("2012-05-15T13:57:57.0000000+00:00").ToUniversalTime()
    Dim b As Date
    b = New Date(1970, 2, 1, 0, 0, 0, DateTimeKind.Utc)
    a.Subtract(b).TotalMilliseconds
    '1334411877000 Same as javascript
    'Note that in javascript, month as 1 is same as 2 in VB.net because months start at 0 in javascript

edited Jul 28, 2012 at 15:16

answered Jul 28, 2012 at 13:29

Esailija

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7 Comments

Eyal Over a year ago

Oy, of course! Replacing Date with DateTimeOffset solves my problem unambigously. I don't like giving a timezone to the Date constructor.

Esailija Over a year ago

@Eyal Why would you want to do that? It's unnecessary moving part. UTC is always the same.

Eyal Over a year ago

The output of your final answer is not 1334411877000.0, it's 1337101077000. ?Date.Parse("1970-01-01T00:00:00.0000000+00:00").Subtract(New Date(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalMilliseconds, by the way, is 72000000. VB.Net's Date.Parse() is ignoring the timezone.

Esailija Over a year ago

@Eyal can you try like this:

DateTime.ParseExact( "2012-05-15T13:57:57.0000000+00:00", "yyyy-MM-ddTHH:mm:ss.fffffffZ",System.Globalization.DateTimeFormatInfo.InvariantCulture)

Esailija Over a year ago

@Eyal or

Date.Parse("2012-05-15T13:57:57.0000000+00:00").TotalMilliSeconds - New Date(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).TotalMilliseconds

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