acces custom button client before - client after

I have a custom page created from a custom view.

In this page I have a custom field and a custom button - nothing is passed to the database - all the operations are made for display only
On the server side I have some time intensive operations and I need to implement a custom wait screen for the user.

In order to do this I need to create an javascript object for the "client before" tab that will start the waiting screen and then I need to close that screen by calling a method in the "client after" for the object created in the client before - something like THIS.
Is it possible to access methods in the "client after" tab for an object created in the "client before" tab?