# fp-ts

> Functional programming in TypeScript

Latest version **2.16.11** (published 2025-08-18) · MIT license · 0 weekly downloads

## Install

```sh
npm install fp-ts
pnpm add fp-ts
yarn add fp-ts
bun add fp-ts
```

## Health

**Score 50/100 (C)** — status: stable.

Positive: has types; esm support; no vulnerabilities; popular repo.

Warnings: low downloads.

Negative: stale.

## Facts

| | |
|---|---|
| Version | 2.16.11 |
| Published | 2025-08-18 |
| First published | 2017-02-11 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Dependencies | 0 |
| Unpacked size | 4.5 MB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| GitHub stars | 11544 |
| Author | Giulio Canti |
| Maintainers | gcanti |
| Keywords | typescript, algebraic-data-types, functional-programming |

## Links

- npm: https://www.npmjs.com/package/fp-ts
- Repository: https://github.com/gcanti/fp-ts
- Issues: https://github.com/gcanti/fp-ts/issues
- npm.io page: https://npm.io/package/fp-ts

## Alternatives

- [@openai/codex-sdk](https://npm.io/package/@openai/codex-sdk.md) — 731.4K weekly downloads
- [babel-plugin-transform-react-jsx](https://npm.io/package/babel-plugin-transform-react-jsx.md) — 565.0K weekly downloads
- [babel-helper-remove-or-void](https://npm.io/package/babel-helper-remove-or-void.md) — 508.5K weekly downloads
- [@pnpm/store-controller-types](https://npm.io/package/@pnpm/store-controller-types.md) — 186.9K weekly downloads
- [react-native-signature-canvas](https://npm.io/package/react-native-signature-canvas.md) — 155.6K weekly downloads

## Recent versions

- 2.16.11 (latest) — 2025-08-18
- 3.0.0-alpha.26 (next) — 2022-09-25
- 2.13.0-rc.6 (rc) — 2022-09-20
- 1.19.5 (old-version-1) — 2019-07-22
- 2.16.10 — 2025-04-18
- 2.16.9 — 2024-07-25
- 2.16.8 — 2024-07-07
- 2.16.7 — 2024-06-29
- 2.16.6 — 2024-05-19
- 2.16.5 — 2024-03-25
- 2.16.4 — 2024-03-18
- 2.16.3 — 2024-03-11
- 2.16.2 — 2024-01-03
- 2.16.1 — 2023-07-27
- 2.16.0 — 2023-05-25
- … 218 more at https://npm.io/package/fp-ts/versions

## README

<h3 align="center">
  <a href="https://gcanti.github.io/fp-ts/">
    <img src="./docs/fp-ts-logo.png">
  </a>
</h3>

<p align="center">
Functional programming in TypeScript
</p>

<p align="center">
  <a href="https://github.com/gcanti/fp-ts/actions">
    <img src="https://github.com/gcanti/fp-ts/actions/workflows/main.yml/badge.svg?branch=master" alt="build status" height="20">
  </a>
  <a href="https://www.npmjs.com/package/fp-ts">
    <img src="https://img.shields.io/npm/dm/fp-ts.svg" alt="npm downloads" height="20">
  </a>
</p>

**📢 Important Announcement: fp-ts is Joining the Effect-TS Ecosystem!**

We are excited to announce that the `fp-ts` project is officially merging with the Effect-TS ecosystem. This is a significant step forward in the functional programming landscape, bringing together two powerful libraries under one roof. Giulio Canti, the author of `fp-ts`, is being welcomed into the Effect organization, promising an exciting future with enhanced capabilities and support.

**What This Means for New Users:**

Effect-TS can be regarded as the successor to `fp-ts v2` and embodies what would be considered `fp-ts v3`. This merger marks a significant evolution in the library's capabilities, integrating more features and functionalities tailored towards robust, type-safe, and scalable functional programming.

For more details on this merger and what it entails, please refer to the official [announcement here](https://dev.to/effect/a-bright-future-for-effect-455m). Additionally, you can explore more about Effect-TS and its offerings on our [website and documentation](https://effect.website/).

# Introduction

`fp-ts` is a library for _typed functional programming_ in TypeScript.

`fp-ts` aims to allow developers to use _popular patterns and abstractions_ that are available in most functional languages. For this, it includes the most popular data types, type classes and abstractions such as [Option](https://gcanti.github.io/fp-ts/modules/Option.ts), [Either](https://gcanti.github.io/fp-ts/modules/Either.ts), [IO](https://gcanti.github.io/fp-ts/modules/IO.ts), [Task](https://gcanti.github.io/fp-ts/modules/Task.ts), [Functor](https://gcanti.github.io/fp-ts/modules/Functor.ts), [Applicative](https://gcanti.github.io/fp-ts/modules/Applicative.ts), [Monad](https://gcanti.github.io/fp-ts/modules/Monad.ts) to empower users to write pure FP apps and libraries built atop higher order abstractions.

A distinctive feature of `fp-ts` with respect to other functional libraries is its implementation of [Higher Kinded Types](<https://en.wikipedia.org/wiki/Kind_(type_theory)>), which TypeScript doesn't support natively.

**Inspired by**

- [Haskell](https://www.haskell.org)
- [PureScript](https://www.purescript.org)
- [Scala](https://www.scala-lang.org)

# Sponsors

<table>
  <tr>
    <td align="center">
      <a href="https://unsplash.com/">
        <img src="https://avatars.githubusercontent.com/u/9951955?s=200&v=4" width="200px;" alt="Unsplash" />
      </a>
      <br />
      <b>Unsplash</b>
      <br />
      <a href="https://unsplash.com/">https://unsplash.com/</a>
      <br />
      <p width="200px">
        The internet’s source for visuals.<br/>
        Powered by creators everywhere.
    </td>
  </tr>
</table>

# Installation

To install the stable version:

```
npm install fp-ts
```

Make sure to always have a single version of `fp-ts` installed in your project. Multiple versions are known to cause `tsc` to hang during compilation. You can check the versions currently installed using `npm ls fp-ts` (make sure there's a single version and all the others are marked as `deduped`).

## TypeScript compatibility

**Strictness** – This library is conceived, tested and is supposed to be consumed by TypeScript with the `strict` flag turned on.

| `fp-ts` version | required `typescript` version |
| --------------- | ----------------------------- |
| 2.0.x+          | 3.5+                          |
| 1.15.x+         | 3.1+                          |
| <= 1.14.4       | 2.8+ (\*)                     |

(\*) If you are running `< typescript@3.0.1` you have to polyfill the `unknown` type. You can use [unknown-ts](https://github.com/gcanti/unknown-ts) as a polyfill.

# Documentation

**Disclaimer**. Teaching functional programming is out of scope of this project, so the documentation assumes you already know what FP is.

- [Docs](https://gcanti.github.io/fp-ts)
- [Learning Resources](https://gcanti.github.io/fp-ts/learning-resources/)
- [Ecosystem](https://gcanti.github.io/fp-ts/ecosystem/)
- API Reference
  - [version 2.x (current)](https://gcanti.github.io/fp-ts/modules/)
  - [version 1.x](https://github.com/gcanti/fp-ts/tree/1.x/docs/modules/)

# Help

If you need help with `fp-ts` check out:

- this [Discord server](https://discord.gg/HVWmBBXM8A)
- the `#fp-ts` channel on [FP slack](https://fpslack.com/).

# Development

- [Code conventions](https://gcanti.github.io/fp-ts/guides/code-conventions)

# License

The MIT License (MIT)

---
_Source: https://npm.io/package/fp-ts · Machine-readable twin of the npm.io package page. Health data is recomputed on every publish._