Confusion about global variables

[jackson]

I tried to set both flow and global variables and I don't think I properly understand how they function. For example, I have a flow that sets a global variable global.GlobalTherm.Temp. When I inject the global variable into a debug using:

[{"id":"120c2b43.843be5","type":"debug","z":"30882327.2d261c","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":440,"y":520,"wires":[]}]

I get { Temp: 65 } which means it's clearly getting stored. However, whenever I try to do anything with that variable, I get a type error. For example:

[{"id":"69b204b.37764fc","type":"function","z":"30882327.2d261c","name":"convert to f","func":"global.GlobalTherm.Diff = global.GlobalTherm.Temp-10\nreturn global;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":550,"y":720,"wires":[["5f0f5493.5ed0ac"]]}]

yields: "TypeError: Cannot read property 'Temp' of undefined". I think I'm just confused about how node red uses global variables, etc. Can someone explain what exactly I'm doing wrong?

[kuema]

In your function node, you need to use global.get('GlobalTherm') instead of global.GlobalTherm.

Here are the docs for reference: Writing Functions : Node-RED

Also, to return the global value from your function node, your can't just return it as is, but return a proper message object.
Just modify the payload of the existing message, something like this should work

let temp = global.get('GlobalTherm');

temp.Diff = temp.Temp - 10;

msg.payload = temp;

return msg;

Be aware that this will return a reference to the same object as in the global context, not a copy. So downstream nodes could work with different data, if other nodes modify the object in the global context.