Do you actually need a date library?
The native Date object and Intl cover most use cases. A library pays for itself when time zones, parsing, or heavy formatting enter the picture.
Native first, library when it hurts
The built-in Date object plus the Intl API format timestamps, compare dates, and localise output in many languages with no dependency at all. That covers more than most projects need.
Does the native JavaScript Date object plus Intl already cover the formatting and comparison my project needs, or
are real time zones involved beyond storing everything in UTC?
When a library earns it
Reach for a library when time zone arithmetic gets messy or parsing across browsers breaks. The two common picks are date-fns (modular, tree-shakeable, import only the functions you use) and Day.js (one tiny chainable object, under 2 KB). Both carry long open-issue lists, because dates are genuinely hard even for mature libraries. Skim those issues for your cases before you commit, so you hit the sharp corner now and not in production.
Compare date-fns and Day.js for my project: [describe my stack, whether bundle size matters, and what date work I need]. Cover bundle size, time zone support, and API style. Then look at each one's open GitHub issues and tell me which unresolved problems would actually bite my use case.
Date plus Intl covers most projects. A date library pays for itself only when time zones or parsing get hard.
Additional Resources
Explore these carefully curated resources to deepen your understanding and practice the concepts covered in this lesson.
date-fns
DocumentationModular date functions you can tree-shake, import only what you use.
https://date-fns.org
Day.js
DocumentationA tiny library (under 2 KB) with a familiar, chainable API for formatting and comparing dates.
https://day.js.org