How to set script label on documents in the UI

makeDialog();

var d, lbl;
function makeDialog(){
  var theDialog = app.dialogs.add({name:"Label Document", canCancel:true});
  with(theDialog){
    with(dialogColumns.add()){
      staticTexts.add({staticLabel:"Open Documents:"});
      staticTexts.add({staticLabel:"Add Label:"});
    }
    with(dialogColumns.add()){
      d = dropdowns.add({stringList:app.documents.everyItem().name, selectedIndex:0, minWidth:150});
      lbl = textEditboxes.add({editContents:"", minWidth:150});
    }
    if(theDialog.show() == true){
      d = app.documents.item(d.selectedIndex);
      d.label = lbl.editContents
      $.writeln(d.label)
      theDialog.destroy();
    }
	}
}