This link which appears at the top of the javascript when selecting it in an automation seem to be broken:
https://api.fibery.io/#action-buttons
It just opens the API reference and their is no section for action buttons.
Looks like it is supposed to go here:
https://the.fibery.io/@public/User_Guide/Guide/Fibery-API-Overview-279#Guide/Scripts-in-Automations-54
The help guides for API were recently migrated from api.fibery.io to the general User Guide. At the moment, any calls to the old pages redirect to the ‘front page’ of the API section of the user guide.
But yeah, the best guide to scripting is the link you provided.
We should probably fix this 
FYI, if you actually want to learn about buttons, they aren’t actually part of the API, so the relevant help page is probably this.