# FxTS [](https://github.com/marpple/FxTS/actions) [](https://www.npmjs.com/package/@fxts/core) [](./LICENSE) FxTS is a functional programming library for TypeScript. - Provides [lazy evaluation](https://fxts.dev/guide/lazy-evaluation) for memory-efficient data processing with functions like [pipe](https://fxts.dev/api/pipe), [map](https://fxts.dev/api/map), [filter](https://fxts.dev/api/filter), and [take](https://fxts.dev/api/take). - Handles [concurrent requests](https://fxts.dev/guide/handle-concurrency) efficiently with [concurrent](https://fxts.dev/guide/concurrent) and [toAsync](https://fxts.dev/api/toAsync). - Offers excellent TypeScript support with strong type inference. - Follows standard [iteration protocols](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Iteration_protocols) (Iterable/AsyncIterable). ## Why FxTS? | | FxTS | lodash | Native (Array + [Iterator Helpers](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Iterator)) | | --------------------------------------------- | ---------------------------------------------------------- | ----------------- | ------------------------------------------------------------------------------------------------------------------------------ | | Lazy evaluation | ✅ | 🔶 `_.chain` only | ✅ ES2025 | | AsyncIterable pipelines | ✅ | ❌ | ❌ (proposal stage) | | Concurrency control with backpressure | ✅ [`concurrentPool`](https://fxts.dev/api/concurrentPool) | ❌ | ❌ | | Curried, data-last composition (`pipe`) | ✅ | 🔶 `lodash/fp` | ❌ | | Early termination across async work (`take`) | ✅ | ❌ | 🔶 sync only | | Literal-preserving inference (`Record<"a"…>`) | ✅ | ❌ | — | | Deep utils (`isEqual`, `cloneDeep`, `merge`) | ✅ | ✅ | ❌ | Migrating from `p-limit`/`p-map`? See the [migration guide](https://fxts.dev/guide/migrate-from-p-map). ## Installation ``` npm install @fxts/core ``` ## Usage Use `pipe` for function composition or `fx` for method chaining: ```ts import { each, filter, fx, map, pipe, range, take } from "@fxts/core"; pipe( range(10), map((a) => a + 10), filter((a) => a % 2 === 0), take(2), each((a) => console.log(a)), ); // chaining fx(range(10)) .map((a) => a + 10) .filter((a) => a % 2 === 0) .take(2) .each((a) => console.log(a)); ``` ## Usage (concurrent) Handle multiple async operations in parallel with `concurrent`: ```ts import { concurrent, countBy, flat, fx, map, pipe, toAsync } from "@fxts/core"; // maybe 1 seconds api const fetchWiki = (page: string) => fetch(`https://en.wikipedia.org/w/api.php?action=parse&page=${page}`); const countWords = async (concurrency: number) => pipe( ["html", "css", "javascript", "typescript"], toAsync, map(fetchWiki), map((res) => res.text()), map((words) => words.split(" ")), flat, concurrent(concurrency), countBy((word) => word), ); await countWords(); // 4 seconds await countWords(2); // 2 seconds ``` ## Documentation For more information, visit [fxts.dev](https://fxts.dev). For LLM-friendly documentation, see [llms.txt](https://fxts.dev/llms.txt). ## Contributing We welcome contributions from everyone in the community. Please read our [Contributing Guide](./CONTRIBUTING.md). ## License Apache License 2.0 © [Marpple](https://www.marpple.com). See [LICENSE](./LICENSE) for details.