Illustrator Scripting: changing stroke or fill of groupItems (not content of a group)

var strokeSize = activeDocument.defaultStrokeWidth;

damn! this one was too easy! 😂

but it makes perfect sense (i will never get used to these default stroke functions.... and i still don't understand why they don't just give us a direct control function for group properties 🤷🏼‍♂)...

thank you soo much for helping me out!

So here's my final Script:

var docRef = app.activeDocument;
var minStrokeWidth = 4;


for (var p=0; p<docRef.pageItems.length; p++) {
    docRef.selection = null;
    var myPI = docRef.pageItems[p];

    if (myPI.constructor.name == "GroupItem") {
        myPI.selected = true;
        var myStrokeWidth = activeDocument.defaultStrokeWidth;
        if (myStrokeWidth < minStrokeWidth) {
            activeDocument.defaultStrokeWidth = minStrokeWidth;
        }
        docRef.selection = null;
    }
}