Event on lost focus field

An advice, please.

How intercept an event "lost focus" in exit on a field of an user input of an ActiveForm?

Lost focus on a field or attempting to close the form entirely or going to another URL?

Right question. Only lost focus on one field. But attempting to closing the form means losing focus on the field. And this it will be not accettable. I must find another way. I need to clear my head. Thank you.

I will open other topic…