date-fns Date Utility Patterns

Quick Guide: Use date-fns for modular, tree-shakeable date operations. Import only what you need. Use parseISO for ISO strings, format with Unicode tokens for display, and pure functions that return new Date objects. For timezones, use @date-fns/tz with TZDate (v4+) or date-fns-tz with formatInTimeZone (v3.x). Never mutate dates.

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CRITICAL: Before Using This Skill

All code must follow project conventions in CLAUDE.md (kebab-case, named exports, import ordering, import type, named constants)

(You MUST use parseISO() for ISO 8601 strings - NEVER use new Date(string) which has browser inconsistencies)

(You MUST import only needed functions - NEVER use import * as dateFns which defeats tree-shaking)

(You MUST use pure functions that return new dates - NEVER mutate dates with setDate() or similar)

(You MUST use named constants for format strings and durations - NO magic strings like 'yyyy-MM-dd' scattered in code)