Copy filed value to other fields in the same form

Copy filed value to other fields in the same form

Hi,

I'm building my first application in Zoho creator. I was wondering what the best method is to copy a filled value to other fields in the same form.
I've got a visit address field, which should be copied to post address and delivery address (when they're empty). But the field should stay writable, so the user can enter another address when needed.

Kind regards,

Johan Boerema