Assuming that the drawing object is a group, how to add a stroke to it using jsfl?

I have some confusion. When the object I select is a drawing object or shape, I can use the following code to add a stroke to it.

fl.getDocumentDOM().selection[0].x += 0;
fl.getDocumentDOM().setStrokeSize(10);

This code cannot take effect on the selected group or symbol.

Using the history function I get code like this:

an.getDocumentDOM().setStroke('#000000', 10, 'solid');

Repeated operations found that this code only takes effect on the drawing object union.

Back to my question:
If the selected object is a group or symbol, the following code cannot stroke it.

customStrokeWidth = 10; 
if (customStrokeWidth) {
  var doc = fl.getDocumentDOM();
  var selection = doc.selection[0];
  myStroke(selection, customStrokeWidth);
}
function  myStroke(element, strokeWidth) {
  if (element.elementType === "group") {
    var elements = element.getElements();
    for (var i = 0; i < elements.length; i++) {
      var nestedElement = elements[i];
      myStroke(nestedElement, strokeWidth);
    }
  } else {
    doc.selection = [element];
    doc.setStrokeSize(strokeWidth);
  }
}​

Did I miss something?