I am working on an extender that will trigger a requirement on a field input. However, I want the input field to be initially blank, only after triggering an initial focus and then blur, do I want to display any error on the page if you have not provided any input on the field.

The problems I have found is:

1. no manual subscription to the observable will be fired if the value has not changed
2. providing events such as 'blur' to the valueUpdate binding won't trigger the change either if original value has not changed
3. I am trying to avoid having to write a custom binding just to trigger the validation.
4. computed's are supposedly always called, but again are based on either being referenced explicitly (i.e. UI) or because an observable they reference has been updated (which again is not triggered because it has not changed).

I like the idea of using an extender an not have to make explicit reference to the validation in the UI by using a binding. But I can't seem to get pass the initial state of being blank and triggering if they focus and blur without any input.

Any suggestions?

vs. knockout 3.0