Read payload from a specific msg.topic

[SwatCat]

Hello, i have a long waiting question.

If i have many msg.topics with msg.payload each, how cand i read (with a function block) a msg.payload for a specific msg.topic??

[E1cid]

Use a join node.
you will find multiple examples here
https://discourse.nodered.org/search?q=join%20messages

Or save inputs to context storage, then you can access anytime
https://nodered.org/docs/user-guide/context

[SwatCat]

i can use SWITCH, but i need it in a function to use them in some conditions.

[Colin]

If you are just trying to route the message down different wires dependent on the topic then use a Switch node, not a function node.

If you do want to do it in a Function node then you can use a javascript switch statement to test the topic and then, for example, to send it to output 2 use
node.send([null, msg, null])
or you can do something clever with a lookup array containing all the topics and find the topic in the array and use the index to build the array to be returned.

[SwatCat]

so.... an IF condition for the msg.topic it will be enough? other easy way?

[Colin]

You don't need to use a new message

if (msg.topic == 1) {
 return [msg]
}

if (msg.topic == 2) {
 return [null, msg]
}