@johnhenry/iteration

npm install @johnhenry/iteration

Zero runtime dependencies. The most mature library in this section — it has shipped under three names across several years.

What’s in it

Transducers — composable transformations that work identically over sync and async iterables, without allocating an intermediate array per step.

itertools parity — the Python itertools surface (chain, cycle, islice, groupby, tee, product, permutations, and the rest) in TypeScript, for both iterator flavours.

Terminal consumers — reduce, collect, first, every, and friends that end a pipeline.

Bounded concurrency — run an async pipeline N-at-a-time without unbounded fan-out.

Cancellation and backpressure — channels that respect a slow consumer rather than buffering without limit, and pipelines that stop promptly when cancelled.

Provenance

The version number is fresh; the code isn’t. This library has been renamed twice:

1. async-itertools — the original, now archived. The 1.x releases and the 2.0 milestones described above (transducer rewrite, cancellation, bounded concurrency, backpressure) all happened under that name.
2. mallory-iteration — absorbed into a pure-TypeScript monorepo, full git history preserved via git subtree.
3. @johnhenry/iteration — the current name, shipping from the johnhenry/math monorepo, restarted at 0.0.0 under the new scope.

If you’re evaluating maturity from the version number, don’t. Read the history instead.