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Manual NodeRED Function Node Patterns
znetsixe edited this page 2026-05-11 22:24:29 +02:00
Node-RED Function Node Patterns (EVOLV Summary)
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Note
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Based on: https://nodered.org/docs/user-guide/writing-functions
Return Semantics
return msg;sends to output 1.return [msg1, msg2, ...];sends one message per output position.- Use
nullfor outputs that should not emit.
Examples:
return [msg, null, null];-> output 1 onlyreturn [null, msg, null];-> output 2 only
Message Mutation Pattern
- Start with the incoming
msg, set fields (msg.topic,msg.payload), then return/send. - This preserves message context unless there is a deliberate reason to create a new object.
Async Function Pattern
- For asynchronous work, call
node.send(...)and thennode.done(). - Avoid returning a message when output is sent asynchronously.
EVOLV Practical Rule
- In example flows (including parsers), always align return-array position with downstream wiring.
- For dashboard parser functions, keep one stable output mapping per metric to avoid wire-level regressions.