Calculating runtime minus Timestamp - google-apps-script

Question

I have a form which activates a procedure via an "On form submit" trigger. At the end of this routine I want to insert the difference in time between the form's Timestamp and the current time at the end of the routine (the difference of which is only a matter of a few seconds).
I've tried many things so far, but the result I typically receive is NaN.
I thought that my best bet would be to construct the runtime elements (H,M,S) and similarly deconstruct the time elements from the entire Timestamp, and then perform a bit of math on that:
var rt_ts = Math.abs(run_time - ts_time);
(btw, I got that formula from somewhere on this site, but I'm obviously grasping at anything at this point. I just can't seem to find a thread where my particular issue is addressed)
I've always found that dealing with dates and time in Javascript is tricky business (ex: the quirk that "month" start at zero while "date" starts at 1. That's unnecessarily mind-bending).
Would anyone care to lead me out of my current "grasping" mindset and guide me towards something resembling a logical approach?

Answer 1

You can simply add this at the top of your onFormSubmit routine :
UserProperties.setProperty('start',new Date().getTime().toString())
and this at the end that will show you the duration in millisecs.
var duration = new Date().getTime()-Number(UserProperties.getProperty('start'))
EDIT following your comment :
the time stamp coming from an onFormSubmit event is the first element of the array returned by e.values see docs here
so I don't really understand what problem you have ??
something like this below should work
var duration = new Date().getTime() - new Date(e.values[0]).getTime();//in millisecs
the value being a string I pass it it 'new Date' to make it a date object again. You can easily check that using the logger like this :
Logger.log(new Date(e.values[0]));//
It will return a complete date value in the form Fri Mar 12 15:00:00 GMT+01:00 2013
But the values will most probably be the same as in my first suggestion since the TimeStamp is the moment when the function is triggered...

Answer 2

I have a function which can show the times in a ss with timestamps in column A. It will also add the time of the script itself to the first timestamp (in row 3) and show this in the Log.
Notice that the google spreadsheet timestamp has a resolution in seconds and the script timestamp in milliseconds. So if you only add, say, 300 milliseconds to a spreadsheet timestamp, it might not show any difference at all if posted back to a spreadsheet. The script below only takes about 40 milliseconds to run, so I have added a Utilities.sleep(0) where you can change the value 0 to above 1000 to show a difference.
function testTime(){
var start = new Date().getTime();
var values = SpreadsheetApp.getActiveSheet().getDataRange().getValues();
for(var i = 2; i < values.length ; i++){
Logger.log(Utilities.formatDate(new Date(values[i][0]),Session.getTimeZone(),'d MMM yy hh:mm:ss' )); // this shows the date, in my case same as the ss timestamp.
Logger.log( new Date(values[i][0]).getTime() ); // this is the date in Milliseconds after 1 Jan 1970
}
Utilities.sleep(0); //you can vary this to see the effects
var endTime = new Date();
var msCumulative = (endTime.getTime() - start);
Logger.log(msCumulative);
var msTot = (msCumulative + new Date(values[2][0]).getTime());
Logger.log('script length in milliseconds ' + msTot );
var finalTime = Utilities.formatDate(new Date(msTot), Session.getTimeZone(), 'dd/MM/yyyy hh:mm:ss');
Logger.log ( finalTime); //Note that unless you change above to Utilities.sleep(1000) or greater number , this logged date/time is going to be identical to the first timestamp since the script runs so quickly, less than 1 second.
}