Moment vs date-fns vs Day.js
The JavaScript date library landscape — why Moment is declining and what to use instead
Weekly Downloads — Last 6 Months
Weekly
28.6M
Monthly
115.9M
Growth
+4%
Bundle (gzip)
75.4 kB
Weekly
46.3M
Monthly
187.1M
Growth
+18%
Bundle (gzip)
17.1 kB
Package Breakdown
The original JavaScript date library — now in maintenance mode
✓ Best For
Maintaining existing Moment codebases only — not recommended for new projects
✗ Weakness
67kB gzipped, mutable, not tree-shakeable, officially in maintenance mode
Functional, tree-shakeable date utilities for modern JavaScript
✓ Best For
Projects using tree-shaking, TypeScript projects (excellent types), functional programming style, and when you only need a subset of date functions
✗ Weakness
More verbose API than Moment or Day.js, no plugin system
2kB Moment.js alternative with a compatible API
✓ Best For
Migrating from Moment.js, projects needing a small bundle footprint, and teams who prefer Moment's chaining API over functional style
✗ Weakness
Plugin system required for advanced features, smaller than date-fns for complex needs
Which Date Library Should You Use in 2026?
For new projects, the choice is between date-fns and Day.js. Use date-fns if you're TypeScript-heavy and want the most comprehensive, tree-shakeable solution. Use Day.js if you want the smallest possible bundle or are migrating from Moment.js.
Do not use Moment.js for new projects. The maintainers themselves have deprecated it. The bundle cost alone is reason enough, but the mutability issues and lack of tree-shaking make it the wrong choice by any modern metric.
For migrating existing Moment.js code, Day.js is the fastest path — most code works with only import changes.
Recommended: dayjs
Smallest bundle (2kB), Moment-compatible API for easy migration, and growing faster than date-fns.
Which to Use For Each Use Case
| Use Case | Winner |
|---|---|
| New project, need date formatting | dayjs |
| TypeScript project with complex date logic | date-fns |
| Migrating from Moment.js | dayjs |
| Need only 2-3 date functions | date-fns |
FAQ
Is Moment.js dead?+
How hard is it to migrate from Moment to Day.js?+
Should I use date-fns or Day.js?+
What about the native JavaScript Temporal API?+
Related Comparisons
Moment.js was the definitive JavaScript date library for nearly a decade. Its comprehensive API, reliable parsing, and broad compatibility made it the default choice for any date manipulation need. But Moment has a critical flaw by modern standards — it's mutable and ships 67kB gzipped, an enormous cost for a utility library. The Moment team itself declared the library in maintenance mode in 2020 and recommends alternatives.
This comparison tells one of the clearest stories in the npm trends dataset: Moment's absolute download numbers remain high (legacy projects haven't switched), but the trend line is declining while date-fns and Day.js are both growing. New projects are not choosing Moment.
The Decline of Moment and Rise of Alternatives
Moment's problems became apparent as JavaScript ecosystem priorities shifted. Tree-shaking became standard — but Moment can't be tree-shaken because it extends a single object. Bundle size became a key metric — Moment's 67kB gzip cost is hard to justify for date formatting. Immutability became a best practice — Moment mutates dates in place, causing subtle bugs.
date-fns addressed all three: it's fully tree-shakeable (only import what you use), immutable, and provides a functional programming model where every function takes a date and returns a new date. The tradeoff is a more verbose API — instead of moment(date).add(1, 'day').format('MM/DD/YYYY'), you chain individual functions.
Day.js chose a different tradeoff: maintain Moment's familiar API (so migration is trivial) but rebuild it as a 2kB immutable library. Most Moment code works in Day.js with only import changes. This Moment API compatibility made it the easiest migration path and drove rapid adoption.
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