API

All exports below come from @rdlabo/workers-timezone. timeZone? uses the initialized default,
or Asia/Tokyo before initialization. See Timezones for error and DST behavior.

Configuration

function initializeTimezone

initializeTimezone(config: TimezoneConfig): Readonly<TimezoneConfig> sets the default once.

function getTimezoneConfig

getTimezoneConfig(): Readonly<TimezoneConfig> returns the active configuration.

Conversions

function toLocalDate

toLocalDate(instant: Date, timeZone?: TimeZone): BusinessDate returns YYYY-MM-DD.

function toLocalDateTime

toLocalDateTime(instant: Date, timeZone?: TimeZone): BusinessDateTime returns YYYY-MM-DD HH:mm:ss.

function localDateTimeToInstant

localDateTimeToInstant(date: BusinessDate, time: string, timeZone?: TimeZone): Date
resolves a local wall clock. The time accepts H:mm or HH:mm, optionally with seconds.

function startOfDay

startOfDay(date: BusinessDate, timeZone?: TimeZone): Date returns the first instant of the day.

function endOfDay

endOfDay(date: BusinessDate, timeZone?: TimeZone): Date returns its final whole second.

function addDays

addDays(date: BusinessDate, days: number): BusinessDate adds an integer number of calendar days.

Additional calendar helpers

today(reference?: Date, timeZone?: TimeZone) returns a calendar date.
normalizeBusinessDate(value: string | Date | null | undefined, timeZone?: TimeZone) returns a
calendar date or null. Prefer ISO strings with an explicit offset for instant-like inputs.
formatBusinessDateTime(instant, pattern?, timeZone?) supports YYYY, MM, DD, hh, mm,
ss, and S tokens; DEFAULT_BUSINESS_DATETIME_PATTERN is YYYY-MM-DDThh:mm:ss.
parseBusinessDateTime(value: BusinessDateTime, timeZone?: TimeZone): Date parses a local
YYYY-MM-DD HH:mm:ss value (a T separator is also accepted).
ageOnBusinessDate(birthDate: BusinessDate, asOfDate?: BusinessDate): number calculates completed
years of age; the reference defaults to today().

Types and constants

TIME_ZONES contains common IANA IDs. TimeZone also accepts other supported IANA strings.
TimezoneConfig contains timeZone. BusinessDate and BusinessDateTime are string aliases,
not runtime validators. BusinessTimeZone and BusinessTimeConfig are compatibility type aliases.
BUSINESS_TIMEZONE is the legacy Tokyo descriptor, not the current configured timezone.

Compatibility exports: toBusinessDate, toBusinessDateTime, businessDateTimeInstant,
startOfBusinessDay, endOfBusinessDay, and addBusinessDays alias the corresponding functions above.
BUSINESS_TIME_ZONES, initializeBusinessTime, and getBusinessTimeConfig alias the timezone
constants and configuration functions.