code: def onerror(self, emitter, message, source, lineno, colno):
          
          self._log.debug("""App.onerror event occurred in webpage: 
              \nMESSAGE:%s\nSOURCE:%s\nLINENO:%s\nCOLNO:%s\n"""%(message, source, lineno, colno))
docs: WebPage Event that occurs on webpage errors