Manipulation Methods

Methods for date arithmetic, boundary queries, month length inspection, and leap year checks. All manipulation methods return new BanglaCalendar instances without mutating the original.

Method Overview

Method	Description
addDays()	Adds or subtracts days.
addWeeks()	Adds or subtracts weeks (7-day intervals).
addMonths()	Adds or subtracts months with optional day overflow clamping.
addYears()	Adds or subtracts years with leap year handling.
startOfMonth()	Returns instance set to 1st day of current month.
endOfMonth()	Returns instance set to last day of current month.
startOfYear()	Returns instance set to 1 Boishakh (১ বৈশাখ).
endOfYear()	Returns instance set to 30 Choitro (৩০ চৈত্র).
daysInMonth()	Returns number of days in specified month (or current month).
isLeapYear()	Checks if current year is a leap year according to variant rules.

---

Details & Examples

addDays()

addDays(days: number): BanglaCalendar

Adds or subtracts specified number of days from current date.

const date = new BanglaCalendar('১৪৩০', '১', '১');

const in7Days = date.addDays(7);   // 8 Boishakh 1430
const ago3Days = date.addDays(-3); // 28 Choitro 1429

---

addWeeks()

addWeeks(weeks: number): BanglaCalendar

Adds or subtracts specified number of weeks (each week = 7 days).

const date = new BanglaCalendar('১৪৩০', '১', '১');

const in2Weeks = date.addWeeks(2); // 15 Boishakh 1430

---

addMonths()

addMonths(months: number, overflow?: boolean): BanglaCalendar

Adds or subtracts months. Parameter overflow (default true):

• true: Invalid dates overflow into the next month.
• false: Clamps to the last valid day of the target month.

const date = new BanglaCalendar('১৪৩০', '৬', '৩১'); // 31 Ashwin

const overflowed = date.addMonths(1);        // 1 Ogrohayon 1430 (overflow)
const clamped = date.addMonths(1, false);     // 30 Kartik 1430 (clamped)

---

addYears()

addYears(years: number, overflow?: boolean): BanglaCalendar

Adds or subtracts years. Handles leap year differences in Falgun when overflow = false.

const date = new BanglaCalendar('১৪৩০', '১', '১৫');

const nextYear = date.addYears(1); // 15 Boishakh 1431

---

startOfMonth()

startOfMonth(): BanglaCalendar

Returns a new instance set to day 1 of the current month.

const date = new BanglaCalendar('১৪৩০', '৫', '১৫');
console.log(date.startOfMonth().toJSON()); // "১৪৩০-০৫-০১"

---

endOfMonth()

endOfMonth(): BanglaCalendar

Returns a new instance set to the last day of the current month (29, 30, or 31 depending on month & leap year).

const date = new BanglaCalendar('১৪৩০', '৫', '১৫');
console.log(date.endOfMonth().toJSON()); // "১৪৩০-০৫-৩১"

---

startOfYear()

startOfYear(): BanglaCalendar

Returns a new instance set to 1 Boishakh (১ বৈশাখ) of the current year.

const date = new BanglaCalendar('১৪৩০', '৫', '১৫');
console.log(date.startOfYear().toJSON()); // "১৪৩০-০১-০১"

---

endOfYear()

endOfYear(): BanglaCalendar

Returns a new instance set to 30 Choitro (৩০ চৈত্র) of the current year.

const date = new BanglaCalendar('১৪৩০', '৫', '১৫');
console.log(date.endOfYear().toJSON()); // "১৪৩০-১২-৩০"

---

daysInMonth()

daysInMonth(month?: NumberRange<1, 12>): NumberRange<29, 31>

Gets the number of days in the specified month (1-12) or the current month if omitted.

const date = new BanglaCalendar('১৪৩০', '১', '১');

console.log(date.daysInMonth());   // 31 (Boishakh)
console.log(date.daysInMonth(11)); // 29 (Falgun in normal year)

---

isLeapYear()

isLeapYear(): boolean

Returns true if the year is a leap year under the active variant rules.

• 'revised-2019': Follows Gregorian leap year rules.
• 'revised-1966': Follows bnYear % 4 === 2 rule.

const date = new BanglaCalendar(1430, 1, 1);
console.log(date.isLeapYear()); // false