iamkun/dayjs

Choose this fork if your goal is to study or teach Day.js internals. Do not choose it for production adoption unless you are prepared to rebase onto upstream yourself, because it is stale and materially behind current Day.js.

Prefer upstream Day.js unless you specifically need this exact frozen fork state. The fork shows no unique functionality and is materially behind upstream, so it adds risk without clear adopter benefit.

Prefer upstream Day.js unless you explicitly need a frozen 2020 snapshot; this fork adds no clear user-facing benefits and is too far behind for routine adoption.

Prefer upstream for almost any new or maintained project. This fork is best treated as a stale frozen copy: it adds no visible features, lags far behind, and is only defensible if you explicitly need the 2019 state unchanged.

Do not adopt this fork for new work. Use upstream Day.js unless you specifically need an untouched 2019 snapshot.

Prefer upstream for almost all new or maintained projects. Choose this fork only if you need its older snapshot and specific locale/type changes, and you are prepared to own the maintenance gap.

Choose this fork only if you specifically need its older snapshot or fork-local documentation/test changes. For most adopters, upstream Day.js is the better default because this fork is stale and far behind current maintenance.

Prefer this fork only if the nil-check fix solves a concrete issue for you. For general use, upstream Day.js is the better choice because this fork is tiny, narrow, and materially behind.

Prefer this fork only if you want a lighter, customized Day.js base and can accept divergence plus weaker upstream tooling. If you want a stable drop-in date library with active maintenance, upstream Day.js is the safer choice.