Comparing
2KB immutable date time library alternative to Moment.js with the same modern API
RFC9562 UUIDs
| Metric | dayjs | uuid |
|---|---|---|
| Ecosystem | npm | npm |
| Difficulty | Intermediate | Intermediate |
| Weekly downloads | 43.9M | 242.6M↑ |
| Latest version | v1.11.20 | v13.0.0 |
| Recipes | 1 | 7↑ |
dayjs only
Shared
uuid only
Use Day.js when you need date parsing, formatting, arithmetic (add/subtract days/months), or comparisons in browser code where bundle size matters. Its plugin system covers timezones, relative time ('3 hours ago'), duration, and ISO weeks.
Use uuid whenever you need a unique ID that doesn't require a database sequence: primary keys in distributed systems, idempotency keys for API calls, session tokens, file names, or correlation IDs for logging.
For complex timezone-aware calendar applications, consider Temporal (the upcoming TC39 proposal) or date-fns with explicit timezone handling. Day.js's plugin system can grow large if you need many features.
For database primary keys where you control the DB, auto-incrementing integers are smaller and faster to index. For sortable unique IDs (e.g. for pagination), consider ULID or UUIDv7, which encode a timestamp prefix.
dayjs
uuid
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