code: func prettyError(vm *otto.Otto, err error, w io.Writer) {
  	failure := err.Error()
  	if ottoErr, ok := err.(*otto.Error); ok {
  		failure = ottoErr.String()
  	}
  	fmt.Fprint(w, ErrorColor("%s", failure))
  }
docs: // prettyError writes err to standard output.