code: def _get_js_files(cls, extra_files):
          
          return cls._get_media_files(
              packager=Packager(),
              media_packages=getattr(cls, 'js_packages', {}),
              media_type='js',
              extra_files=extra_files)
docs: Return all JavaScript files from the Media class.
  
          Args:
              extra_files (list):
                  The contents of the Media class's original :py:attr:`js`
                  attribute, if one was provided.
  
          Returns:
              list:
              The JavaScript files to return for the :py:attr:`js` attribute.