# Confusion about global variables
**URL:** https://discourse.nodered.org/t/confusion-about-global-variables/50420
**Category:** General
**Created:** [31 August 2021 03:48 UTC](https://discourse.nodered.org/t/confusion-about-global-variables/50420 "2021-08-31T03:48:33Z")
**Posts on this page:** 3
**Page:** 1
### Author:  [@jackson](https://discourse.nodered.org/u/jackson)
#### Post date: [31 August 2021 03:48 UTC](https://discourse.nodered.org/t/confusion-about-global-variables/50420/1 "2021-08-31T03:48:33Z")
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?
---
### Author:  [@kuema](https://discourse.nodered.org/u/kuema)
#### Post date: [31 August 2021 05:00 UTC](https://discourse.nodered.org/t/confusion-about-global-variables/50420/2 "2021-08-31T05:00:16Z")
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](https://nodered.org/docs/user-guide/writing-functions#global)
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
```auto
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.
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [30 October 2021 05:00 UTC](https://discourse.nodered.org/t/confusion-about-global-variables/50420/3 "2021-10-30T05:00:17Z")
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