get activeDocument through BridgeTalk onResult

var bt = new BridgeTalk();
bt.target = BridgeTalk.appSpecifier;
bt.body = 'targetFunction();';
bt.onResult = function(resObj){
	doc = app.activeDocument;
	grp = doc.groupItems;
	for(var i=0; i<grp.length; i++){
	// loop for groupitems
	}
	palette.layout.layout(true);
	palette.show();
};
bt.send();

I am creating a script for redrawing a palette in Script UI.

However, when I try to access the activeDocument within the BridgeTalk.onResult callback, it doesn't work. It seems like the rest of the script is functioning properly. How can I make this work?