Function isFastDay

isFastDay(date: number | HDate | Date, il?: boolean): boolean
Returns true if the given date is observed as a major or minor fast day.

Major fasts: Yom Kippur, Tish'a B'Av. Minor fasts: Tzom Gedaliah, Asara B'Tevet, Ta'anit Esther, Ta'anit Bechorot, Tzom Tammuz (plus BeHaB fasts when enabled).

Erev Tish'a B'Av — even though the fast begins at sunset — is not counted here: only the actual fast day itself returns true. Postponed fasts return true on the actual observed date (e.g. when 17 Tammuz falls on Shabbat and is observed on the 18th).
Parameters
- date: number | HDate | Date
  Hebrew Date, Gregorian date, or absolute R.D. day number
- Optionalil: boolean
  use the Israeli schedule for holidays
Returns boolean
true if the date is a major or minor fast day
Example
```
import {isFastDay, HDate, months} from '@hebcal/core';
isFastDay(new HDate(10, months.TISHREI, 5784)); // true  (Yom Kippur)
isFastDay(new HDate(11, months.TISHREI, 5784)); // false
```
- Defined in src/isFastDay.ts:27