date-fns Date Utility Library

date-fns is a free and open-source, modern JavaScript date utility library that provides the most comprehensive, yet simple and consistent toolset for manipulating JavaScript dates. Created by Sasha Koss and Lesha Koss (date-fns team) in 2015, date-fns is designed as a modern, modular, and functional alternative to Moment.js, following the success of Lodash in the utility library space. Used by over 12 million projects. Key features: modular: date-fns is built as a collection of independent functions. Each function (format, parse, addDays, subMonths, isAfter, differenceInDays) is a separate module, enabling tree-shaking. Import only what you need (import { format, addDays } from 'date-fns'). This results in significantly smaller bundle sizes compared to Moment.js (which bundles all functionality in ~70 KB). Immutable and pure: all functions are pure (no side effects) and return new Date objects, never mutating the input. This prevents bugs from accidental mutations. Functional API: functions follow a consistent data-last signature (e.g., addDays(date, amount), format(date, 'yyyy-MM-dd')). This enables currying and composition with libraries like Ramda. Comprehensive: over 200 functions covering formatting, parsing, arithmetic (add, subtract), comparison (isBefore, isAfter, isEqual), ranges (startOfDay, endOfMonth), durations, and timezone operations. Localization: built-in internationalization with over 70 locales. Import only the needed locale (import { fr } from 'date-fns/locale'). Time zones: timezone support via date-fns-tz package, which provides functions for converting between time zones using IANA timezone names. TypeScript: full TypeScript definitions. date-fns v3 supports both ESM and CommonJS. JavaScript/TypeScript. MIT.