# Composable for Node.js (mercury-nodejs)

> A lightweight Event-over-HTTP function host and client: write decoupled functions in
> JavaScript/TypeScript and let Mercury Composable engines (Java, Rust) orchestrate them
> from Event Script flows and MiniGraph knowledge graphs. Orchestration stays in the
> engines; this package provides functions plus the engines' operational conventions
> (configuration, logging, trace, actuators). The engines' documentation lives at
> https://accenture.github.io/mercury-composable/ (its llms.txt maps the three layers).

> This file is the machine-readable map of this documentation site.

## Start here
- [Home](https://accenture.github.io/mercury-nodejs/): the three-layer theme and where a Node.js function sits (a leaf peer over Event-over-HTTP).
- [AI Agent Guide](https://accenture.github.io/mercury-nodejs/guides/ai-agent-guide/): **start here if you are an AI agent** — the complete authoring grammar on one page: contract, registration, composition, config keys, error rules.
- [Getting Started](https://accenture.github.io/mercury-nodejs/guides/getting-started/): a running function in five minutes, called from an engine flow.

## Foundations
- [Rationale](https://accenture.github.io/mercury-nodejs/guides/rationale/): why externalized functions — ecosystem gravity, the Event-over-HTTP seam, why the wrapper owns nothing but functions.
- [Design](https://accenture.github.io/mercury-nodejs/guides/design/): the anatomy — envelope codec, Event API host, primitive anycast bus (why not EventEmitter; faithful instances/isPrivate), PostOffice, actuators — and the minimalist rulings.

## Write functions
- [Function Writing Patterns](https://accenture.github.io/mercury-nodejs/guides/function-patterns/): the (headers, body) contract, the never-block-the-loop rule, AppException, trace context, private functions, composition.
- [Configuration, Logging & Actuators](https://accenture.github.io/mercury-nodejs/guides/config-logging-actuators/): resources convention, -D overrides, three log formats, actuator endpoints, health-function contract, Kubernetes probes.
- [Testing Your Functions](https://accenture.github.io/mercury-nodejs/guides/testing/): handler tests, fresh-registry bus tests, real-HTTP host tests, golden wire vectors.

## Join the engines
- [Join an Event Script Flow](https://accenture.github.io/mercury-nodejs/guides/join-event-script/): yaml.event.over.http, the flow task, what the function sees, the exception path.
- [Join a Knowledge Graph](https://accenture.github.io/mercury-nodejs/guides/join-knowledge-graph/): graph.task to a declarative target (engines >= v4.11.11), deadlines, the error.* contract.

## Reference
- [Configuration Reference](https://accenture.github.io/mercury-nodejs/guides/configuration-reference/): every well-known key, resolution order, substitution syntax.
- [HTTP Surface Reference](https://accenture.github.io/mercury-nodejs/guides/http-surface-reference/): /api/event protocol, actuator shapes, error signature, content types.
- [Release Notes](https://github.com/Accenture/mercury-nodejs/blob/main/CHANGELOG.md)