Illustrator Scripting. How to merge|unite groups together?

[Robin232607161l9m]

I selected all groups on the page

app.activeDocument.groupItems[i].selected = true;

and then tried to merge|unite them with 

app.executeMenuCommand("Live Pathfinder Merge");

but, it doesn't work.

Illustrator opens with selected groups but they are split

Could you please help with it?

[femkeblanco]

https://community.adobe.com/t5/illustrator-discussions/looking-for-javascript-commands-for-path-find...