Working with a date field

Working with a date field

I am using an on User Input script to process the value entered in a date field. My problem is that if the user just types in a date the on User Input script is not executed.  It only seems to work when the date is selected by clicking on the calendar icon. 

What is the best way to work around this shortcoming? Is there a way to prevent the user from typing anything in the date field so they are forced to click on the calendar icon? 

Thanks,

Ken