code: def to_json_(self) -> str:
          
          try:
              renderer = pytablewriter.JsonTableWriter
              data = self._build_export(renderer)
              return data
          except Exception as e:
              self.err(e, "Can not convert data to json")
docs: Convert the main dataframe to json
  
          :return: json data
          :rtype: str
  
          :example: ``ds.to_json_()``