Dates, parsing & validation

The BSDate type, the supported range, parsing, and validating year/month/day combinations.

interface BSDate { year: number; month: number; day: number }

A Bikram Sambat calendar date, as a plain object. month is 1-based — 1 is Baisakh, 12 is Chaitra. Nothing stops you building an invalid one like { year: 2083, month: 13, day: 1 }, so every function that takes a BSDate validates it first and throws InvalidBSDateError if it isn't real. Functions return new objects and never modify their arguments.

type Weekday = 0 | 1 | 2 | 3 | 4 | 5 | 6

A day of the week, numbered like Date#getDay(): 0 is Sunday, 6 is Saturday.

const MIN_BS_YEAR = 1979
const MAX_BS_YEAR = 2100

The inclusive bounds of the supported BS years, corresponding to AD 1922-04-13 to 2044-04-13.

function parseBsDate(value: string): BSDate

Parses "YYYY-MM-DD" (zero-padded, ASCII digits, nothing before or after), the form formatBsDate produces by default. Throws BSDateFormatError if the string isn't shaped like that, or InvalidBSDateError if it is but isn't a real date (e.g. "2083-13-01"). For Nepali digits, convert with fromNepaliDigits first.

Validation

function isValidBsDate(date: BSDate): boolean

Reports whether date is a real Bikram Sambat date in the supported range — checked against that month's actual length, not just a generic 1–32 bound. Never throws: NaN, Infinity, fractional numbers, non-numbers and non-objects (including null) all return false.

function isSupportedBsYear(year: number): boolean

Reports whether year is an integer from MIN_BS_YEAR to MAX_BS_YEAR.

function daysInBsMonth(year: number, month: number): number

The number of days (29–32) in the given BS month. Throws InvalidBSDateError if the year or month is out of range.

function daysInBsYear(year: number): number

The total number of days in the given BS year. Throws InvalidBSDateError if the year is out of range.

Example

import {
  MAX_BS_YEAR,
  MIN_BS_YEAR,
  daysInBsMonth,
  daysInBsYear,
  isSupportedBsYear,
  isValidBsDate,
  parseBsDate,
} from "bikram-sambat-ts";
 
parseBsDate("2083-06-06"); // { year: 2083, month: 6, day: 6 }
parseBsDate("2083/06/06"); // throws BSDateFormatError
parseBsDate("2083-13-01"); // throws InvalidBSDateError (field: "month")
 
isValidBsDate({ year: 2083, month: 9, day: 32 }); // false — Poush 2083 only has 30 days
isValidBsDate({ year: 2083, month: NaN, day: 1 }); // false
isSupportedBsYear(2101); // false
 
daysInBsMonth(2083, 6); // 31
daysInBsYear(2083); // 365
[MIN_BS_YEAR, MAX_BS_YEAR]; // [1979, 2100]

ⓘ

JavaScript numbers can be things a Go int never is — NaN, Infinity, 1.5. This package rejects all of them explicitly (isValidBsDate returns false, everything else throws), rather than letting them quietly produce a wrong date.