FxTS is a functional programming library for TypeScript.
- Provides lazy evaluation for memory-efficient data processing with functions like pipe, map, filter, and take.
- Handles concurrent requests efficiently with concurrent and toAsync.
- Built on the standard iteration protocols - LLM SDK streams, Node.js streams, and paginated APIs are pipelines out of the box.
- Offers excellent TypeScript support with strong type inference.
| FxTS | lodash | Native (Array + Iterator Helpers) | |
|---|---|---|---|
| Lazy evaluation | ✅ | 🔶 _.chain only |
✅ ES2025 |
| AsyncIterable pipelines | ✅ | ❌ | ❌ (proposal stage) |
| Concurrency control with backpressure | ✅ concurrentPool |
❌ | ❌ |
Curried, data-last composition (pipe) |
✅ | 🔶 lodash/fp |
❌ |
Promise-unwrapping composition (pipe infers Awaited values) |
✅ | ❌ | ❌ |
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.
npm install @fxts/core
Use pipe for function composition or fx for method chaining:
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));Handle multiple async operations in parallel with concurrent:
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 secondsFor more information, visit fxts.dev.
For LLM-friendly documentation, see llms.txt.
We welcome contributions from everyone in the community. Please read our Contributing Guide.