Need to write a client script based on date difference.

[Aditya Sinha]

I have a field 'D' in my catalog form. I need to write a  catalog client script to ensure that if a date entered in field D is lesser than 30 days from the current date, it needs to clear D's value and show an error message. 

[Brad Bowman]

Your catalog client script would need to call a Script Include to do this properly.  Try this low-code approach instead

https://www.servicenow.com/community/developer-articles/no-code-date-validations-through-catalog-ui-...