JavaScript's built-in Date has barely changed since 1995, and it carries every design flaw of that era. Months are zero-indexed, time zone behavior defaults to local time in confusing ways, and Date instances are mutable, making them dangerous to share between functions. Real applications quickly hit the limits of Date and reach for a third-party library.
Choosing between libraries comes down to five axes: bundle size, API design, time zone support, internationalization, and active maintenance. Bundle size dominates on the front end where every kilobyte affects load time, while server-side correctness and readability often win out on the back end. It is common for a single project to use different libraries on the client and server.
Moment.js dominated the JavaScript date scene from its 2011 launch through the late 2010s. Its rich API, fluent method chaining, and excellent internationalization made it the obvious choice. In 2020, the maintainers themselves declared the project a legacy library and discouraged its use in new code. The reasons are mutability, lack of tree-shaking, and a roughly 290 KB bundle size that hurts modern web apps.
Wholesale migration is hard because Moment's API is pervasive. Most teams adopt a phased approach: write all new code with a modern library and replace existing Moment usage during natural touchpoints. Moment continues to receive security patches but has effectively frozen its feature set.
Day.js launched in 2018 with the explicit goal of providing a Moment-compatible API in a fraction of the size. The core bundle is around 7 KB, less than 1/40th of Moment. Time zone, relative time, and locale support come as opt-in plugins, so applications pay only for what they use. dayjs("2026-05-18").add(1, "day").format("YYYY-MM-DD") works exactly as it did in Moment, making this the easiest migration target.
Day.js does not match Moment feature-for-feature, so check compatibility for advanced APIs before committing. Its time zone plugin uses Intl.DateTimeFormat under the hood, which means it can fail in Node.js builds with reduced ICU data. Knowing this constraint upfront saves debugging time when deploying to minimal runtime environments.
date-fns takes a different philosophical stance with a functional API: every operation is a top-level function that takes a Date and returns a new Date. There is no proprietary class, just standard Date instances flowing through pure functions. Tree-shaking works perfectly, so a project using only format and addDays ships just a few kilobytes. TypeScript inference is flawless thanks to the explicit argument types.
The trade-off is that the API style differs sharply from Moment-flavored chaining. format(date, "yyyy-MM-dd") looks unfamiliar to developers used to date.format(...). Time zone operations require the separate date-fns-tz package, which adds about 12 KB but provides full IANA support. Many new projects pick date-fns specifically for the bundle savings.
Luxon was created by a Moment maintainer to address the architectural mistakes of the original. It is immutable, modern, and designed around full IANA time zone support. DateTime.fromISO("2026-05-18T09:00", { zone: "Asia/Tokyo" }) creates a fully zoned datetime in one call. The DST handling, calendar math, and formatting are best-in-class for applications where time zones are central.
Luxon depends heavily on Intl, which means older browsers or trimmed-down Node.js builds may need additional polyfills. The bundle is larger than date-fns but smaller than Moment, and the readability of its zoned datetime APIs often justifies the size for applications heavy in scheduling or international logistics.
The Temporal proposal is at Stage 3 in the ECMAScript process and is gradually arriving in browsers. It introduces a family of immutable types (PlainDate, PlainTime, PlainDateTime, ZonedDateTime, Instant) that cleanly separate concerns. Temporal also supports calendar systems beyond Gregorian, including Japanese era and Hebrew calendars, as a first-class language feature.
As of mid-2026, Temporal is not yet universally available, so production use requires the @js-temporal/polyfill. Once browsers ship native implementations, third-party libraries become optional in many cases. New projects can plausibly start with Temporal plus a polyfill today and shed the polyfill later, positioning themselves to be free of Day.js, Luxon, and date-fns within a few years.
If your needs are limited to formatting and trivial arithmetic, native Date plus Intl.DateTimeFormat is enough. For bundle-conscious frontends, prefer date-fns or Day.js. For backend services with heavy time zone work or multilingual rendering, Luxon's API is hard to beat. For greenfield projects with a long horizon, Temporal plus polyfill is the most future-proof choice.
The bigger error is sticking with Moment by inertia. Each year you defer migration, the security patches and dependency upgrades pile up, and the eventual rewrite gets harder. New code should adopt a modern library immediately, with old Moment usage cleaned up incrementally. Most teams find that a 90-day migration plan is enough to stop adding new Moment dependencies, even if full removal takes longer.
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