code: def load_if_not_loaded(widget, filenames, verbose=False, delay=0.1, force=False, local=True, evaluator=None):
      
      if evaluator is None:
          evaluator = EVALUATOR  # default if not specified.
      for filename in filenames:
          loaded = False
          if force or not filename in LOADED_JAVASCRIPT:
              js_text = get_text_from_file_name(filename, local)
              if verbose:
                  print("loading javascript file", filename, "with", evaluator)
              evaluator(widget, js_text)
              LOADED_JAVASCRIPT.add(filename)
              loaded = True
          else:
              if verbose:
                  print ("not reloading javascript file", filename)
          if loaded and delay > 0:
              if verbose:
                  print ("delaying to allow JS interpreter to sync.")
              time.sleep(delay)
docs: Load a javascript file to the Jupyter notebook context,
      unless it was already loaded.