Noob set flow variable question

[vkuehn]

Accroding to the documentation it should work to set variables from a function node to the flow like that.

if (flow.get("bot_command")!==undefined){
    flow.set("bot_command", "c0,0");
}
msg.payload = flow.get('bot_command');
return msg;

Also that didn't work

do I have to prepare something before using flow variables ?

[gerry]

I think the expression should be
== 'undefined'

[vkuehn]

@gerry That did actually work, thanks.
Would you know how to do the same in a change node ?

[knolleary]

You cannot do a 'set if not defined' type of rule in the Change node, but aside from that, you can set a flow context value. In the screenshot you've shared, I can see you were using msg.paylod and not msg.payload.

[Colin]

@vkuehn

if (flow.get("bot_command")!==undefined)

That says that if it is not undefined then set it. Perhaps you meant if it is undefined then set it.

if (flow.get("bot_command")===undefined){

that syntax is frowned on, however, as the name undefined can be set to a value. An alternative is

if (typeof(flow.get("bot_command")) === "undefined"){

or, if know that the variable should never be zero or false or an empty string then you can use

msg.payload = flow.get("bot_command")  ||  "c0,0"
flow.set("bot_command",msg.payload)
return msg

[vkuehn]

@knolleary thanks changing it to payload did work....sorry posting a typo
it would be nice if that is possible
@Colin thanks for the hints