Simplest JavaScript Datetime library: ream.js

Features:

Functional Programming: Pure functions and immutable data structures

Real Timezone Database: Full IANA timezone support with automatic DST detection

DST Handling: Accurate daylight saving time transitions and calculations

Calendar Arithmetic: Safe date/time arithmetic with overflow handling

Formatting System: Comprehensive token-based formatting with locale support

Duration Operations: Monoid operations and humanization

Recurrence Generators: Flexible recurring date/time patterns

Plugin System: Extensible architecture for custom functionality

TypeScript: Full TypeScript support with comprehensive type definitions

Zero Dependencies: Uses built-in Intl API for timezone data