Hello @Jana Smith,
For this problem you can create one action(contains us logic, js, etc.) in screen and assign same action to "OnAfterFetch" of all aggregates and also same action call in "OnInitialize" of screen.
OR
Another way is same as mentioned by @Vikas Sharma you can create on data action for that screen call all aggregates in that and call you js in "OnAfterFetch" action of that Data action.
Regards,
Narendra Bhangale.