EVOLV/wiki/manuals/node-red/runtime-node-js.md

# Node-RED Runtime Node JS Manual (EVOLV Summary)

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Based on: https://nodered.org/docs/creating-nodes/node-js

## Input Handler Contract

- Node-RED calls runtime handlers as `function(msg, send, done)`.
- For compatibility, custom nodes should support fallback behavior when `send` is not provided.
- Use `done()` on successful completion and `done(err)` on failure.

## Output Routing Rules

- For single-output nodes: `send(msg)` sends on output 1.
- For multi-output nodes: pass an array with one slot per output, for example:
  - `[msg, null, null]` => output 1 only
  - `[null, msg, null]` => output 2 only
- Always construct the outbound message first, then send it.

## EVOLV Runtime Pattern

Recommended runtime input structure for `src/nodeClass.js`:

1. Normalize `send` fallback.
2. Wrap `switch(msg.topic)` in `try/catch`.
3. Route response messages to explicit output index with array format.
4. Call `done()`/`done(err)` consistently.

## Common Failure Mode

- Sending a bare object in a multi-output context can hide intended port routing.
- In EVOLV nodes with 3 outputs (`process`, `dbase`, `parent`), use explicit arrays for deterministic wiring behavior.