using System;

​

public class Program

{

    public static void Main()

    {

        var a = DateTime.Now;

        var b = DateTime.Now;

        Console.WriteLine(a.ToJavaScriptMilliseconds1());

        Console.WriteLine(a.ToJavaScriptMilliseconds2());

        Console.WriteLine(DateTimeJavaScriptConverter.FromJavaScriptMilliseconds(a.ToJavaScriptMilliseconds1()));

        Console.WriteLine(DateTimeJavaScriptConverter.FromJavaScriptMilliseconds(a.ToJavaScriptMilliseconds2()));

    }

}

​

internal static class DateTimeJavaScriptConverter

{

    private static readonly long _datetimeMinTimeTicks = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc).Ticks;

    public static long ToJavaScriptMilliseconds1(this DateTime dt)

    {

        return (dt.ToUniversalTime().Ticks - _datetimeMinTimeTicks) / 10000;

    }

​

    public static long ToJavaScriptMilliseconds2(this DateTime dt)

    {

        return (((DateTimeOffset)dt).ToUnixTimeMilliseconds());

    }

​

    public static DateTime FromJavaScriptMilliseconds(long milliseconds)

    {

        return new DateTime(ticks: (milliseconds * 10000) + _datetimeMinTimeTicks);

    }

}