# Effection — Structured Concurrency for JavaScript

Effection is a JavaScript library for building reliable asynchronous and
concurrent programs using **structured concurrency**.

Effection models async work as **lazy operations** with explicit lifetimes,
deterministic cancellation, and guaranteed cleanup. It uses **generator
functions (`function*`)**, not `async` / `await`, to express long-lived,
cancellable work.

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## ⚠️ IMPORTANT FOR AI AGENTS

If you will **write, modify, refactor, or debug Effection code**, you **must**
read [AGENTS.md] first.

**AGENTS.md is the normative behavioral contract.**
- Do not invent APIs
- Do not infer semantics from Promises or other ecosystems
- Do not substitute primitives that “look equivalent”
- If information is missing or uncertain, consult the API reference

If any other document conflicts with AGENTS.md, **AGENTS.md takes precedence**.

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## Where to look (routing)

- **Behavioral rules & invariants (authoritative):** [AGENTS.md]
- **Public API reference (authoritative):** [API]
- **Conceptual guides & explanations (human-oriented):** [Guides]
  - [Thinking in Effection]
  - [Async Rosetta Stone]
  - [Operations]
  - [Scope]
  - [Resources]
  - [Spawn]
  - [Collections]
  - [Browse all guides][docs/]
- **Extension packages (process, fetch, websockets, WebWorkers):** [EffectionX]

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[AGENTS.md]: https://raw.githubusercontent.com/thefrontside/effection/v4/AGENTS.md
[API]: https://frontside.com/effection/api/
[Guides]: https://frontside.com/effection/guides/v4
[Thinking in Effection]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/thinking-in-effection.mdx
[Async Rosetta Stone]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/async-rosetta-stone.mdx
[Operations]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/operations.mdx
[Scope]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/scope.mdx
[Resources]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/resources.mdx
[Spawn]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/spawn.mdx
[Collections]: https://raw.githubusercontent.com/thefrontside/effection/v4/docs/collections.mdx
[EffectionX]: https://frontside.com/effection/x/