Oct 02, 2017 09:42 AM|Cathy Zou|LINK
Because I have other .net controls on the page like textboxes which have required field validation, I would like to provide a very similar validation experience for all the controls rather than having an alert just for the dropdown.
You could use Validating ASP.NET Server Controls, which only works for server control.
So, you have to use the code above I provided in previous reply to validate your select element.
You could do some change in js base on your requirement..e.g when the user doesn't select the dropdown, the focus should be on the dropdown and perhaps provide error text rather than alert?