# Writing global context by using the content of a variable instead of a property in quotation marks

**URL:** <https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132>\
**Category:** General\
**Tags:** function-node\
**Created:** [17 October 2022 09:18 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132 "2022-10-17T09:18:25Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![Gulpman](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gulpman/32/4452_2.png) [@Gulpman](https://discourse.nodered.org/u/Gulpman)\
**Post date:** [17 October 2022 09:18 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/1 "2022-10-17T09:18:25Z")

</div>

Hi everybody,

I am trying to write to a global context using a variable as first parameter instead of a hard-coded string but am strugling about what the syntax for that is.

If I am running the following code within a function node, it works flawlessly:

```auto
global.set("NewEnvironment.Abstellkammer.Climate.temperature", msg.payload.temperature, "file");
global.set("NewEnvironment.Abstellkammer.Climate.humidity", msg.payload.humidity, "file");

return msg;

```

(Abstellkammer = lumber room)

However, if I want to dynamically set the global context (don't know the exact name for this, I'm talking about the first parameter of global.set(...)) I am struggling to find the right syntax.

```auto
var myEnvironment = "NewEnvironment.";

myEnvironment = myEnvironment + msg.payload.RoomName + ".";
myEnvironment = myEnvironment + msg.payload.SensorType + ".";

global.set(myEnvironment, msg.payload.temperature, "file");
global.set(myEnvironment, msg.payload.humidity, "file");

return msg;

```

throws an error message:

```auto
"Error: Invalid property expression: unterminated expression"

```

I tried to find out about properties and tried different syntax to use my variable instead of a hard-coded first parameter, but have not been successful.

What I would like to achive, is that I am using the variable myEnvironment within the global.set function.

At the moment I'm helping myself out with using a gigantic switch node which takes care about the room name at first and duplicate versions of my function where the RoomName and SensorTypes are hard-coded.

Unfortunately I'm struggling on this tiny syntax thing here - as I think it should be possible to pass a variable there.

Any help is much appreciated.

Best  
Sascha

---

<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [17 October 2022 09:34 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/2 "2022-10-17T09:34:22Z")

</div>

Try adding `node.warn` to see what is happening...

```auto
let myEnvironment = "NewEnvironment.";

myEnvironment = myEnvironment + msg.payload.RoomName + ".";
myEnvironment = myEnvironment + msg.payload.SensorType + ".";

node.warn( { 
  "myEnvironment": myEnvironment,
  "msg.payload.temperature": msg.payload.temperature,
  "msg.payload.humidity": msg.payload.humidity
})

global.set(myEnvironment, msg.payload.temperature, "file");
global.set(myEnvironment, msg.payload.humidity, "file");

return msg;

```

* * *

NOTE:

this part...

```auto
global.set(myEnvironment, msg.payload.temperature, "file");
global.set(myEnvironment, msg.payload.humidity, "file");

```

essentially sets `global[myEnvironment]` to `msg.payload.temperature` then immediately overwirtes it with `msg.payload.humidity`

What are you really trying to achieve?

---

<div class="post-metadata">

**Author:** ![Gulpman](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gulpman/32/4452_2.png) [@Gulpman](https://discourse.nodered.org/u/Gulpman)\
**Post date:** [17 October 2022 11:24 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/3 "2022-10-17T11:24:11Z")

</div>

Hi @Steve-Mcl  
thank you very much for your fast reply.

> [...]  
> essentially sets `global[myEnvironment]` to `msg.payload.temperature` then immediately overwirtes it with `msg.payload.humidity`  
> What are you really trying to achieve?

I don't know why I didn't see this when I tried what felt like 100 alternatives, but reading "immediately overwrites..." helped me to find the error instantaneously. 🤦

I changed the code to the following, which is leading to the desired result:

```auto
var myEnvironment = "NewEnvironment.";

myEnvironment = myEnvironment + msg.payload.RoomName + ".";
myEnvironment = myEnvironment + msg.payload.SensorType + ".";

var myEnvTemp = myEnvironment + "temperature";
var myEnvHum = myEnvironment + "humidity";

global.set(myEnvTemp, msg.payload.temperature, "file");
global.set(myEnvHum, msg.payload.humidity, "file");

return msg;

```

The resulting structure then is:

```auto
{"Abstellkammer":{"Climate":{"temperature":24.58,"humidity":63.88}}}

```

which is, what my intention was. 🙂

And after I check-read this posting, further sensor data arrived into the structure, proving the correctness:

```auto
{"Abstellkammer":{"Climate":{"temperature":24.43,"humidity":58.72}},
"Wohnzimmer":{"Climate":{"temperature":22.23,"humidity":65.25}},
"Terrasse":{"Climate":{"temperature":20.88,"humidity":85.18}},
"Bad":{"Climate":{"temperature":23.53,"humidity":88.97}}} 

```

🙂

Thank you very much for your help @Steve-Mcl

---

<div class="post-metadata">

**Author:** ![Steve-Mcl](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/steve-mcl/32/4826_2.png) [@Steve-Mcl](https://discourse.nodered.org/u/Steve-Mcl)\
**Post date:** [17 October 2022 11:50 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/4 "2022-10-17T11:50:49Z")

</div>

Glad it's sorted & you understand what/why etc 🙂

Here are some other approached...

```javascript
const room = msg.payload.RoomName
const sensorType = msg.payload.SensorType
const data = {temperature: msg.payload.temperature, humidity: msg.payload.humidity}
global.set(`${room}.${sensorType}`, data, "file");

```

```javascript
const room = global.get(msg.payload.RoomName, "file") || {}
const sensor = room[msg.payload.SensorType] || {}
sensor.temperature = msg.payload.temperature
sensor.humidity = msg.payload.humidity
room[msg.payload.SensorType] = thisSensor
global.set(msg.payload.RoomName, room, "file");

```

maybe they will help you get a deeper understanding?

---

<div class="post-metadata">

**Author:** ![Gulpman](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/gulpman/32/4452_2.png) [@Gulpman](https://discourse.nodered.org/u/Gulpman)\
**Post date:** [17 October 2022 13:43 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/5 "2022-10-17T13:43:39Z")

</div>

Indeed that helps a lot in understanding - and saving many, many try & errors on my side 😅

---

<div class="post-metadata">

**Author:** ![system](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/1X/d073cd938eafa2e558d7c2cd59003b3ef4963033.png) [@system](https://discourse.nodered.org/u/system)\
**Post date:** [31 October 2022 13:44 UTC](https://discourse.nodered.org/t/writing-global-context-by-using-the-content-of-a-variable-instead-of-a-property-in-quotation-marks/69132/6 "2022-10-31T13:44:23Z")

</div>

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