Conversion

Converting between Gregorian (AD) and Bikram Sambat (BS), and today's date in Nepal.

function adToBs(date: Date): BSDate

Converts a Gregorian date to Bikram Sambat. Only the calendar date matters: the result depends on date's local year, month and day (getFullYear(), getMonth(), getDate()), and the time of day is ignored. Throws DateOutOfRangeError if the date is before AD 1922-04-13 or after AD 2044-04-13, and TypeError if date isn't a Date or is an Invalid Date.

function bsToAd(date: BSDate): Date

Converts a Bikram Sambat date to a new Date at local midnight of the corresponding Gregorian day, so its getFullYear(), getMonth() and getDate() are the AD date, and passing it back to adToBs gives the original BS date. Throws InvalidBSDateError if date isn't a real, supported BS date.

function todayBs(now?: Date): BSDate

Today's date in Nepal (Nepal Standard Time, UTC+05:45) as a BS date, whatever timezone the code runs in. Pass now to ask about another instant. Throws DateOutOfRangeError if that date in Nepal is outside BS 1979–2100. Matches go-bs's TodayBS.

Example

import { adToBs, bsToAd, todayBs } from "bikram-sambat-ts";
 
adToBs(new Date(2026, 8, 22)); // { year: 2083, month: 6, day: 6 }
adToBs(new Date(2026, 8, 22, 23, 59)); // { year: 2083, month: 6, day: 6 } (time of day ignored)
 
bsToAd({ year: 2083, month: 6, day: 6 }).toDateString(); // "Tue Sep 22 2026"
 
// 20:00 UTC on 22 September 2026 is already 01:45 on the 23rd in Nepal.
todayBs(new Date("2026-09-22T20:00:00Z")); // { year: 2083, month: 6, day: 7 }

Timezone behavior

This package converts calendar dates, not instants. A JavaScript Date is an instant, so the package reads the local calendar consistently in both directions: adToBs reads the local year/month/day, and bsToAd returns local midnight. So adToBs(bsToAd(x)) is always x, in any timezone, and daylight saving never shifts a result (all day arithmetic uses UTC day numbers internally). This mirrors go-bs, where ADToBS reads the time.Time's year, month and day as expressed.

Two things to watch for:

new Date("2026-09-22") is UTC midnight, not local midnight — that's how JavaScript parses a date-only ISO string. West of UTC its local date is still the 21st:
```
// Running in America/Los_Angeles:
adToBs(new Date("2026-09-22")); // { year: 2083, month: 6, day: 5 }  (local date: Sep 21)
adToBs(new Date("2026-09-22T00:00")); // { year: 2083, month: 6, day: 6 }  (local midnight)
```
Use new Date(2026, 8, 22) or new Date("2026-09-22T00:00") when you mean a calendar date.
adToBs(new Date()) gives today in the runtime's timezone. In a browser that's the user's own day. On a server running in UTC (the usual default for cloud VMs and containers), it's still yesterday in Nepal for the 5 h 45 min after Nepal's midnight. Use todayBs() whenever "today" should mean today in Nepal.

ⓘ

A handful of timezones skipped a whole calendar day when they moved across the International Date Line — in this range, 1994-12-31 in Pacific/Kiritimati and 2011-12-30 in Pacific/Apia. No Date has that day as its local date, so there bsToAd for the matching BS day returns the following day. The test suite runs in 9 timezones, including both of those.

ⓘ

Every one of the 44,562 supported days round-trips exactly in both directions, and is checked against go-bs's own output for the same day — see calendar data.