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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_js_files(cls, extra_files):
 """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. """

        return cls._get_media_files(
            packager=Packager(),
            media_packages=getattr(cls, 'js_packages', {}),
            media_type='js',
            extra_files=extra_files)