datefnstz

Datefnstz is a JavaScript library that provides time zone support for date-fns, enabling reliable time zone conversions and zone-aware formatting of dates. It is designed to complement date-fns by offering operations that respect IANA time zones and daylight saving rules.

Key features include: support for IANA time zone identifiers (for example America/New_York), handling of daylight saving time transitions, conversion between UTC and a target time zone, formatting a date according to a specified time zone, and parsing strings that include or imply a time zone. The library aims to be modular and tree-shakeable, integrating with the existing date-fns API without replacing its core date handling.

Implementation and design: datefnstz relies on the IANA time zone database and the Intl API where available to determine offsets and DST rules. It provides pure, deterministic functions that do not mutate inputs and are compatible with standard JavaScript Date objects and numeric timestamps. It emphasizes predictable results across environments, including browsers and Node.js.

Usage: The library is typically installed via a package manager and imported into a project using date-fns workflows. Typical usage involves converting a moment in time to a target zone and then formatting or outputting that value in that zone, enabling developers to display user-specific times or perform zone-aware calculations.

See also: date-fns, date-fns-tz, time zone databases, IANA TZ database.