I followed the Max Zieb instructions about using chatGPT and I've got this running code for me:
// Get an array of the names of all timelines
let timelineNames = ["attivita1", "attivita2", "attivita3"];
// Generate a random index from 0 to 2
let randomIndex = Math.floor(Math.random() * 3);
// Pick the timeline at the random index
let timelineName = timelineNames[randomIndex];
// Start the randomized timeline
hypeDocument.startTimelineNamed(timelineName, hypeDocument.kDirectionForward);