Can't get most basic jsonata expression right in change node. I need to route mesage to two different outputs depending on the topic ... (topic = "A") seems to work but boolean (topic = "B" or topic = "C") doesn't. Thanks.
If you want to route two different message types, not sure why you want a change node since this can be done with a switch node and without JSONata.
I meant switch node. How do you route in case of (topic = "B" or topic = "C")
Sorry, I did A, B and everything else. Adjust as needed of course. Also note that I've changed the setting at the bottom to stop after match rather than check all. Not sure how much difference this makes but it seems more logical to me and I wish it were the default to be honest.
For first output 1 need it to be A (no problem with that), for output 2 I need to be B "or" C
Add all 3 & connect the B and C outputs together with a junction node or direct to the next node.
Ok, or can just send B and C into the same place (without junction node)? I just wanted to do a jsonata boolean, didn't expect that wouldn't be able to solve it.
Yes, certainly. A junction can be convenient though and may help keep the visuals tidy.
JSONata can certainly do the job but it is a rather large industrial steam hammer to knock in a nail. 
JSONata adds significant overheads to your flow and is generally best kept for when nothing else fits or you need an object re-shaping (which is what it was originally for I believe).
You don't need a junction node, just feed the two outputs to the same place.
The output of $$.topic ="B" or $$.topic = "C" is a boolean so just add that as the expression.
e.g.
[{"id":"01a5fa39c9c56b5a","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"A","payload":"1","payloadType":"str","x":870,"y":7760,"wires":[["5742f760b0672199"]]},{"id":"5742f760b0672199","type":"switch","z":"d1395164b4eec73e","name":"","property":"topic","propertyType":"msg","rules":[{"t":"eq","v":"A","vt":"str"},{"t":"jsonata_exp","v":"$$.topic = \"B\" or $$.topic = \"C\"","vt":"jsonata"}],"checkall":"true","repair":false,"outputs":2,"x":1070,"y":7780,"wires":[["d890d64db2e56f8a"],["d09f296836f763f2"]]},{"id":"02b40896f488c50d","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"B","payload":"2","payloadType":"str","x":870,"y":7820,"wires":[["5742f760b0672199"]]},{"id":"f539489f4164f71c","type":"inject","z":"d1395164b4eec73e","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"C","payload":"3","payloadType":"str","x":870,"y":7880,"wires":[["5742f760b0672199"]]},{"id":"d890d64db2e56f8a","type":"debug","z":"d1395164b4eec73e","name":"debug 2575","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1250,"y":7760,"wires":[]},{"id":"d09f296836f763f2","type":"debug","z":"d1395164b4eec73e","name":"debug 2576","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"false","statusVal":"","statusType":"auto","x":1250,"y":7800,"wires":[]}]
Or if those are the only two outputs ("a" , "b" or "c") you could always use otherwise for second rule.
