react-day-picker/src/contexts/DayPicker/formatters/formatYearCaption.ts

Customizable Date Picker for React

import { format } from 'date-fns';

/**
 * The default formatter for the Year caption.
 */
export function formatYearCaption(
  year: Date,
  options?: { locale?: Locale }
): string {
  return format(year, 'yyyy', options);
}