Get to know which one is active Stroke or Fill for the document.

I've found this thread in 2024. This is what works in Illustrator 28.4.1:

var isStroke = app.isStrokeActive() ? true : false;
if(isStroke){
  var tmpObj = doc.defaultStrokeColor;
}else{
  var tmpObj = doc.defaultFillColor;
}
alert([tmpObj.red, tmpObj.green, tmpObj.blue,].join(', '));

I think as far as script is concerned the object is selected from that you can access and change either… Only the GUI has the change either fill/stroke by making it foremost… oh and the swapper