# How do I set and then reference a global variable in an expression?

**URL:** <https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679>\
**Category:** General\
**Tags:** function-node, home-assistant\
**Created:** [4 December 2022 18:01 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679 "2022-12-04T18:01:12Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![UngluedChalice](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/ungluedchalice/32/71941_2.png) [@UngluedChalice](https://discourse.nodered.org/u/UngluedChalice)\
**Post date:** [4 December 2022 18:01 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679/1 "2022-12-04T18:01:12Z")

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I'm using Node Red 13.5.3 in Home Assistant and using a `call service` node that is part of the Home Assistant "node package" (not sure what the proper term is).

I want to set my shades to not close all the way in the winter so condensation doesn't build up.

Currently, if I want to set the shades to a certain setting I use the expression `{"position": 5` in the `call-service` node when calling the `set_cover_position` service in Home Assistant.

Instead of manually changing every single node to `{"position": 5}` and then to `{"position": 0}` when I want them to fully close again in the spring, I would like to set something (maybe it is called a Global Variable, I'm not sure, that's what I've tried so far). So instead of the expression `{"position": 30}`, I would do something like `{"position": GLOBAL_VARIABLE}`. Then I could change that global variable in one location and it would essentially update it for all nodes that reference it.

I tried to declare a global variable by typing `global.set("shade_closed_setting", "5")` in a function node. I'm not sure how to tell if I was successful or not.

Then I've just been guessing and testing to try to get it to work in the expression, but I have not been successful.  
Some of the things I've tried:  
`{"position": global.get("shade_closed_setting")}`  
`{"position": "global.shade_closed_setting"}`  
`{"position": global.shade_closed_setting}`

And I feel like I could keep guessing and testing forever. Unfortunately, I don't know any programming languages, which is probably the issue here.

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [4 December 2022 18:20 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679/2 "2022-12-04T18:20:41Z")

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You would select JSONata J: from the type input. Then you can use

```auto
{"position": $globalContext("shade_closed_setting")}

```

[edit] fixed typo

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<div class="post-metadata">

**Author:** ![UngluedChalice](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/ungluedchalice/32/71941_2.png) [@UngluedChalice](https://discourse.nodered.org/u/UngluedChalice)\
**Post date:** [4 December 2022 18:54 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679/3 "2022-12-04T18:54:20Z")

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Thank you, this allowed me to figure it out. The exact code you provided didn't work, but the debug node said "Did you mean $globalContext?" so I put the $ sign in and it worked!

Also, it needed it still as the expression rather than the JSON.

 ![Screen Shot 2022-12-04 at 12.52.39 PM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/0/0/00223cf50ec8c499d6fcee6e4dc4fbdd2af5b583.png)

`{ "position": $globalContext("shade_closed_setting")}`  
is the code that worked in the end

with  
`global.set("shade_closed_setting", 5)`  
in the function node in the "On Start" tab.

Thanks again!

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<div class="post-metadata">

**Author:** ![E1cid](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/e1cid/32/77971_2.png) [@E1cid](https://discourse.nodered.org/u/E1cid)\
**Post date:** [4 December 2022 18:57 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679/4 "2022-12-04T18:57:53Z")

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Yes I said use JSONata J: not JSON.

Glad you sorted it and figured out my typo in the example code. I corrected it above as to not mislead others.

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**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [18 December 2022 18:58 UTC](https://discourse.nodered.org/t/how-do-i-set-and-then-reference-a-global-variable-in-an-expression/71679/5 "2022-12-18T18:58:50Z")

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