How to get the date back from datepicker into Code.gs in google apps script for spreadsheet

How to get the date back from datepicker into Code.gs in google apps script for spreadsheet

Thanks to contributors on google+ and stackoverflow I now have a google spreadsheet with a script and a form attached, with which the club's newsletter editor can export items from the club's calendar and get them nicely formatted in the spreadsheet, ready for further editing and printing to a PDF file for distribution to the club members. The editor can fill in the form to specify the starting and ending dates, and the script does the rest.

But I would rather use datepicker so s/he can select the starting and ending months to fetch from the calendar as soon as the spreadsheet opens, driven by the function "onOpen".

I have found many examples of how to tweak datepicker to offer different date formats, but I have not been able to find any example that shows how to get the selected date back from the file created by google's HTML Service into a variable in the script file, "Code.gs". It seems everybody knows how to get variables back from the HTML file into the script code, so they don't write about it. But I'm stumped.

Can you please point me to any documentation on how to do that.

Thanks, Jim