30 lines
1006 B
Markdown
30 lines
1006 B
Markdown
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# Node-RED Function Node Patterns (EVOLV Summary)
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Based on: https://nodered.org/docs/user-guide/writing-functions
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## Return Semantics
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- `return msg;` sends to output 1.
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- `return [msg1, msg2, ...];` sends one message per output position.
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- Use `null` for outputs that should not emit.
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Examples:
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- `return [msg, null, null];` -> output 1 only
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- `return [null, msg, null];` -> output 2 only
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## Message Mutation Pattern
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- Start with the incoming `msg`, set fields (`msg.topic`, `msg.payload`), then return/send.
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- This preserves message context unless there is a deliberate reason to create a new object.
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## Async Function Pattern
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- For asynchronous work, call `node.send(...)` and then `node.done()`.
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- Avoid returning a message when output is sent asynchronously.
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## EVOLV Practical Rule
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- In example flows (including parsers), always align return-array position with downstream wiring.
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- For dashboard parser functions, keep one stable output mapping per metric to avoid wire-level regressions.
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