Day.js is a lightweight JavaScript date/time library (approximately 2 kB gzipped) designed as a drop-in alternative to Moment.js. It provides immutable, chainable parsing, validation, manipulation, formatting, and comparison APIs, along with extensive internationalization support via over 100 locale files. The library is built as a modular core with a plugin system that extends functionality without bloating the base bundle. It runs in both browsers and Node.js, includes TypeScript definitions, and has a comprehensive test suite that ensures behavioral parity with Moment.js. This is a library, not an application or data pipeline—there are no server components, CLI tools, or data analysis artifacts. The architecture is intentionally small and focused, with a constant-driven unit system and a clean separation between core, plugins, and locales.
This repository is a highly configurable, feature-rich React date picker component library published as `react-datepicker`. It provides a single entry point (`DatePicker`) that supports single date, date range, multiple dates, week, month, quarter, and year picker modes, along with time selection, timezone handling, localization via `date-fns`, and extensive keyboard navigation and ARIA accessibility. Internally, the library uses a class-component architecture with a clear separation of concerns: a `Calendar` component manages month/year navigation, `Month` renders days or month/quarter grids, `Day` handles individual cell rendering with selection and focus management, and `Time`/`InputTime` handle time input. Positioning of the calendar popover is delegated to `@floating-ui/react` via a `withFloating` HOC, and rendering can be redirected to a portal (including shadow DOM) for overlay scenarios. The component exposes over 60 props for customization, including custom input elements, headers, and day rendering. The library is mature and widely adopted, with a comprehensive test suite (Jest + React Testing Library) covering interactions, keyboard navigation, edge cases, and accessibility (axe tests). The build pipeline uses Rollup to produce UMD, CJS, and ES module bundles, and CSS is provided in both standard and CSS Modules variants.