code: def add_user_js(self, js_list):
          
          if isinstance(js_list, string_types):
              js_list = [js_list]
          for js_path in js_list:
              if js_path and js_path not in self.user_js:
                  if js_path.startswith("http:"):
                      self.user_js.append({
                          'path_url': js_path,
                          'contents': '',
                      })
                  elif not os.path.exists(js_path):
                      raise IOError('%s user js file not found' % (js_path,))
                  else:
                      with codecs.open(js_path,
                                       encoding=self.encoding) as js_file:
                          self.user_js.append({
                              'path_url': utils.get_path_url(js_path,
                                                             self.relative),
                              'contents': js_file.read(),
                          })
docs: Adds supplementary user javascript files to the presentation. The
              ``js_list`` arg can be either a ``list`` or a string.