react-day-picker/src/contexts/Modifiers/utils/isDateInRange.ts

Customizable Date Picker for React

import { differenceInCalendarDays, isSameDay } from 'date-fns';

import { DateRange } from 'types/Matchers';

/** Return `true` whether `date` is inside `range`. */
export function isDateInRange(date: Date, range: DateRange): boolean {
  let { from, to } = range;
  if (from && to) {
    const isRangeInverted = differenceInCalendarDays(to, from) < 0;
    if (isRangeInverted) {
      [from, to] = [to, from];
    }
    const isInRange =
      differenceInCalendarDays(date, from) >= 0 &&
      differenceInCalendarDays(to, date) >= 0;
    return isInRange;
  }
  if (to) {
    return isSameDay(to, date);
  }
  if (from) {
    return isSameDay(from, date);
  }
  return false;
}