Comparing
Modern JavaScript date utility library
Create your next immutable state by mutating the current one
| Metric | date-fns | immer |
|---|---|---|
| Ecosystem | npm | npm |
| Difficulty | Intermediate | Beginner ✓ |
| Weekly downloads | 71.4M↑ | 41.7M |
| Latest version | v4.1.0 | v11.1.4 |
| Recipes | 2↑ | 1 |
date-fns only
Shared
immer only
Use date-fns for formatting, parsing, arithmetic (add/subtract days, months, years), comparison, and locale-aware output in any JavaScript environment. Import only what you need and the bundle impact is minimal.
Use Immer whenever you have deeply nested state updates that are painful to write immutably: Redux reducers, Zustand's set function, or React useState with complex objects. It's built into Redux Toolkit's createSlice, so you're probably already using it.
date-fns v2 has limited first-party timezone support — for complex timezone-aware applications use Luxon or the Temporal polyfill. The function-heavy API can feel verbose for simple one-liners; Day.js's method chaining is more readable in those cases.
For flat, simple state (a counter, a boolean toggle), immer's overhead isn't worth it — just spread the object. Immer also has edge cases with classes, Maps, and Sets that require using enableMapSet() and enableAllPlugins().
date-fns
immer