Joget DX 8 Stable Released
The stable release for Joget DX 8 is now available, with a focus on UX and Governance.
I think "Bean Shell Load() method" you are referring to is in Bean Shell Programming Guide#UseasFormLoadBinderFormLoadBinder
This method will only be invoked upon the submission of the whole form, so, as follow up, the event "clicking of a button in a form" is correct but it does not seem like you want to submit the whole form.
Can you clarify on what you want to achieve on making a select box selection (first select/change)?
You might be interested with this - Dynamic Cascading Drop-Down List
How to call Bean Shell Load () method on selection of a dropdown or clicking of a button in a form ?