Representations of time can differ significantly between programming languages. I recently mixed some .Net code and JavaScript code and had to make some conversions between time representations. This code is generally useful and is being placed here for those who find themselves looking for a quick conversion. Let’s jump into the code.

const long DOTNET_JAVASCRIPT_EPOCH_DIFFERENCE = 621_355_968_000_000_000;
static long DotNetDateToJavaScriptTicks(DateTime d)
{
    return (d.Ticks - DOTNET_JAVASCRIPT_EPOCH_DIFFERENCE) / 10_000;
}

static DateTime JavaScriptTicksToDotNetDate(long ticks)
{
    long dticks = ticks * 10_000 + DOTNET_JAVASCRIPT_EPOCH_DIFFERENCE;
    var retVal = new DateTime(dticks );
    return retVal;
}

To test that it was working, I converted from a .Net time to JavaScript ticks and then back to .Net time If all went well, then I should end up with the same time that I started with.

var originalDotNetTime = DateTime.Now.Date.AddHours(15).AddHours(4).AddMinutes(0);
var javaScriptTicks = DotNetDateToJavaScriptTicks(originalDotNetTime) ;
var convertedDotNetTime = JavaScriptTicksToDotNetDate(javaScriptTicks);

if(originalDotNetTime == convertedDotNetTime)
{
    Console.WriteLine("Time Conversion Successful!");
}
else
{
    Console.WriteLine("The conversion was unsuccessful");
}

I ran the code, and it worked! Honestly, it didn’t work the first time because I left a 0 off of 10,000. Adding the underscores (_) to the numbers makes discovering such mistakes easier. Were you to use this code in AWS, note that some values in AWS, such as a TTL field on a DynamoDB table, expect values to be in seconds, not milliseconds. The JavaScript ticks value would have to be divided by 1000 when converted from a .Net time or multiplied by 1000 when being converted back to a .Net time.

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