// From 2.12.0 onward moment.updateLocale('en', { invalidDate : String });

// From 2.8.1 to 2.11.2 moment.locale('en', { invalidDate : String });

// Deprecated in 2.8.1 moment.lang('en', { invalidDate : String });


Locale#invalidDate should be a string.

moment.updateLocale("es", {
  invalidDate: "Fecha invalida"
});