# effection

> Structured concurrency and effects for JavaScript

Latest version **4.1.1** (published 2026-09-03) · MIT license · 0 weekly downloads

## Install

```sh
npm install effection
pnpm add effection
yarn add effection
bun add effection
```

## Health

**Score 70/100 (B)** — status: active.

Positive: has types; esm support; no vulnerabilities; has provenance; recently updated; high maintenance score.

Warnings: low downloads.

## Facts

| | |
|---|---|
| Version | 4.1.1 |
| Published | 2026-09-03 |
| First published | 2018-11-02 |
| Weekly downloads | 0 |
| License | MIT |
| TypeScript types | bundled |
| Module format | ESM + CommonJS |
| Node | >= 16 |
| Dependencies | 0 |
| Unpacked size | 240 KB |
| Known vulnerabilities | 0 |
| Install scripts | no |
| Provenance | attested (GitHub Actions) |
| GitHub stars | 853 |
| Author | engineering@frontside.com |
| Maintainers | frontsidejack |

## Links

- npm: https://www.npmjs.com/package/effection
- Repository: https://github.com/thefrontside/effection
- Homepage: https://github.com/thefrontside/effection#readme
- Issues: https://github.com/thefrontside/effection/issues
- npm.io page: https://npm.io/package/effection

## Recent versions

- 4.1.1 (latest) — 2026-09-03
- 4.1.0-alpha.10 (next) — 2026-07-26
- 4.1.0 — 2026-07-30
- 4.0.4 — 2026-07-25
- 4.0.3 — 2026-06-10
- 4.1.0-alpha.9 — 2026-06-04
- 4.1.0-alpha.8 — 2026-06-02
- 4.1.0-alpha.7 — 2026-03-02
- 4.1.0-alpha.6 — 2026-03-02
- 4.1.0-alpha.5 — 2026-02-20
- 4.1.0-alpha.4 — 2026-02-19
- 4.1.0-alpha.3 — 2026-02-05
- 4.1.0-alpha.2 — 2026-02-05
- 4.1.0-alpha.1 — 2026-02-05
- 4.1.0-alpha.0 — 2026-02-04
- … 324 more at https://npm.io/package/effection/versions

## README

[![npm](https://img.shields.io/npm/v/effection.svg)](https://www.npmjs.com/package/effection)
[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](https://opensource.org/licenses/MIT)
[![Created by Frontside](https://img.shields.io/badge/created%20by-frontside-26abe8.svg)](https://frontside.com)
[![Chat on Discord](https://img.shields.io/discord/700803887132704931?Label=Discord)](https://discord.gg/Ug5nWH8)

# Effection

Structured concurrency and effects for JavaScript.

## Why use Effection?

Effection leverages the idea of [structured concurrency][structured concurrency]
to ensure that you don't leak any resources, effects, and that cancellation is
always properly handled. It helps you build concurrent code that feels rock
solid _at scale_, and it does all of this while feeling like normal JavaScript.

[Learn how to use Effection in your own project](https://frontside.com/effection)

## Platforms

Effection runs on all major JavaScript platforms including NodeJs, Browser, and
Deno. It is published on both [npm][npm-effection] and
[deno.land][deno-land-effection].

## Contributing to Website

Go to [website's readme](www) to learn how to contribute to the website.

## Development

[Deno][Deno] is the primary tool used for development, testing, and packaging.

### Testing

To run tests:

```text
$ deno task test
```

### Building NPM Packages

If you want to build a development version of the NPM package so that you can
link it locally, you can use the `build:npm` script and passing it a version
number. for example:

```text
$ deno task build:npm 3.0.0-mydev-snapshot.0
Task build:npm deno run -A tasks/build-npm.ts "3.0.0-mydev-snapshot.0"
[dnt] Transforming...
[dnt] Running npm install...

up to date, audited 1 package in 162ms

found 0 vulnerabilities
[dnt] Building project...
[dnt] Emitting ESM package...
[dnt] Emitting script package...
[dnt] Complete!
```

Now, the built npm package can be found in the `build/npm` directory.

## For AI Assistants

- [AGENTS.md](AGENTS.md) — Behavioral contract for AI agents working with
  Effection
- [llms.txt](https://frontside.com/effection/llms.txt) — Machine-readable index
  with EffectionX packages

[structured concurrency]: https://vorpus.org/blog/notes-on-structured-concurrency-or-go-statement-considered-harmful/
[discord]: https://discord.gg/Ug5nWH8
[Deno]: https://deno.land
[npm-effection]: https://www.npmjs.com/package/effection
[deno-land-effection]: https://deno.land/x/effection

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