How to set a specific topic to the output of a function node

[Flixm]

Hi,
how can i set the function node to get a specific topic for the calculated output ? e.g.: "Wert"

or much better to get only the result of the calclation, and only if both topics are loaded?

if (msg.topic === "bezug") context.set("W1",msg.payload);
if (msg.topic === "pvplus") context.set("W2",msg.payload);

var W1 = context.get("W1") || 0;
var W2 = context.get("W2") || 0;

msg.payload = W2 - W1;
return msg;

[jbudd]

[{"id":"f666d9b2662603c9","type":"inject","z":"6b7503f72b16f50f","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"bezug","payload":"42","payloadType":"num","x":120,"y":100,"wires":[["823a77b9cbe585d3"]]},{"id":"690bf51451ad3433","type":"inject","z":"6b7503f72b16f50f","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"pvplus","payload":"101","payloadType":"num","x":120,"y":180,"wires":[["823a77b9cbe585d3"]]},{"id":"823a77b9cbe585d3","type":"join","z":"6b7503f72b16f50f","name":"","mode":"custom","build":"object","property":"payload","propertyType":"msg","key":"topic","joiner":"\\n","joinerType":"str","accumulate":true,"timeout":"","count":"2","reduceRight":false,"reduceExp":"","reduceInit":"","reduceInitType":"","reduceFixup":"","x":270,"y":140,"wires":[["1f9983cdfb96e1a1"]]},{"id":"259678b0f2244ed8","type":"change","z":"6b7503f72b16f50f","name":"","rules":[{"t":"set","p":"topic","pt":"msg","to":"Wert","tot":"str"}],"action":"","property":"","from":"","to":"","reg":false,"x":630,"y":140,"wires":[["77c8ae21ad74b861"]]},{"id":"1f9983cdfb96e1a1","type":"change","z":"6b7503f72b16f50f","name":"","rules":[{"t":"set","p":"payload","pt":"msg","to":"payload.bezug - payload.pvplus","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":440,"y":140,"wires":[["259678b0f2244ed8"]]},{"id":"77c8ae21ad74b861","type":"debug","z":"6b7503f72b16f50f","name":"debug 258","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":810,"y":140,"wires":[]}]

[Flixm]

hey,
the first time i tried to work with a function node ... and it´s still easier to solve with standard nodes

[jbudd]

Yup, it;s often a mistake to just reach for a function node.
And you can combine the two change nodes into one for an even sleeker look.