fix(datepicker): fix datepicker format not available error (#1117)

Closes #1088

src/framework/date-fns/services/date-fns-date.service.ts

@@ -25,4 +25,8 @@ export class NbDateFnsDateService extends NbNativeDateService {
  parse(date: string, format: string): Date {
  return parse(date, format, new Date());
  }
+
+ getId(): string {
+ return 'date-fns';
+ }
 }

src/framework/moment/services/moment-date.service.ts

@@ -142,6 +142,10 @@ export class NbMomentDateService extends NbDateService<Moment> {
  return moment();
  }
 
+ getId(): string {
+ return 'moment';
+ }
+
  protected setMomentLocaleData(locale: string) {
  const momentLocaleData = moment.localeData(locale);
 

src/framework/theme/components/calendar-kit/services/date.service.ts

@@ -177,4 +177,6 @@ export abstract class NbDateService<D> {
  * Returns date with added number of years.
  * */
  abstract addYear(date: D, years: number): D;
+
+ abstract getId(): string;
 }

src/framework/theme/components/calendar-kit/services/native-date.service.ts

@@ -155,4 +155,8 @@ export class NbNativeDateService extends NbDateService<Date> {
  isSameYear(date1: Date, date2: Date): boolean {
  return date1.getFullYear() === date2.getFullYear();
  }
+
+ getId(): string {
+ return 'native';
+ }
 }

src/framework/theme/components/datepicker/datepicker.component.ts

@@ -42,7 +42,6 @@ import {
  NbCalendarSize,
  NbCalendarViewMode,
  NbDateService,
- NbNativeDateService,
 } from '../calendar-kit';
 import { NbDatepicker, NbPickerValidatorConfig } from './datepicker.directive';
 
@@ -198,7 +197,7 @@ export abstract class NbBasePicker<D, T, P> extends NbDatepicker<T> implements O
  protected abstract get pickerValueChange(): Observable<T>;
 
  ngOnChanges() {
- if (this.dateService instanceof NbNativeDateService && this.format) {
+ if (this.dateService.getId() === 'native' && this.format) {
  throw new Error('Can\'t format native date. To use custom formatting you have to install @nebular/moment or ' +
  '@nebular/date-fns package and import NbMomentDateModule or NbDateFnsDateModule accordingly.' +
  'More information at "Formatting issue" ' +