# Bug? using \`change\` node (jsonata) to add non-existing flow/global variables generates no error

**URL:** <https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148>\
**Category:** General\
**Created:** [30 August 2022 19:20 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148 "2022-08-30T19:20:39Z")\
**Posts on this page:** 14\
**Page:** 1

<div class="post-metadata">

**Author:** ![zenofmud](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/zenofmud/32/316_2.png) [@zenofmud](https://discourse.nodered.org/u/zenofmud)\
**Post date:** [30 August 2022 19:20 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/1 "2022-08-30T19:20:39Z")

</div>

NR v3.0.2

If you use use jsonata in a `change` node and try to add flow/global variables together and one of the flow/global variables does not exist, no error and no result is returned.

Example flow:

 ![Screen Shot 2022-08-30 at 3.19.16 PM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/b/0/b0f8ad82619b93bc266f123b6dce08e5a34387f4.png)

```auto
[{"id":"1b34f2e69b481f3d","type":"inject","z":"51b4376bd7d81c4b","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"55","payloadType":"num","x":130,"y":120,"wires":[["7c08c8263ebca986"]]},{"id":"7c08c8263ebca986","type":"change","z":"51b4376bd7d81c4b","name":"","rules":[{"t":"set","p":"var1","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":150,"y":180,"wires":[["4204bdfb2b189e0f"]]},{"id":"9ac824b955284c63","type":"debug","z":"51b4376bd7d81c4b","name":"debug 3","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":140,"y":300,"wires":[]},{"id":"92c935c39b9f84fb","type":"catch","z":"51b4376bd7d81c4b","name":"","scope":null,"uncaught":false,"x":340,"y":140,"wires":[["7cc339226879bd18"]]},{"id":"7cc339226879bd18","type":"debug","z":"51b4376bd7d81c4b","name":"debug 4","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":500,"y":140,"wires":[]},{"id":"4204bdfb2b189e0f","type":"change","z":"51b4376bd7d81c4b","name":"add three flow variables together","rules":[{"t":"set","p":"payload","pt":"msg","to":"$flowContext('var1')+$flowContext('var2')+$flowContext('var3')","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":220,"y":240,"wires":[["9ac824b955284c63"]]}]

```

---

<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:** [30 August 2022 19:38 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/2 "2022-08-30T19:38:56Z")

</div>

try

```auto
$sum([
    $flowContext('var1'),
    $flowContext('var2'),
    $flowContext('var3')
])

```

If one is not defined it can not be added using +, but can be sum()'ed.  
There are other cases where the behaviour you see occurs, it can be helpful at time.

---

<div class="post-metadata">

**Author:** ![zenofmud](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/zenofmud/32/316_2.png) [@zenofmud](https://discourse.nodered.org/u/zenofmud)\
**Post date:** [30 August 2022 19:44 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/3 "2022-08-30T19:44:41Z")

</div>

> [@E1cid](#):
>
> If one is not defined it can not be added using +

the question is should it throw an error instead of returning nothing?

---

<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:** [30 August 2022 20:04 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/4 "2022-08-30T20:04:13Z")

</div>

if no property is set as there is an undefined, you then can detect it in flow to continue or not, as said i find this help full at times, as i can stop the flow without error handling from another flow. So my vote is I like it this way.

---

<div class="post-metadata">

**Author:** ![drmibell](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/drmibell/32/8424_2.png) [@drmibell](https://discourse.nodered.org/u/drmibell)\
**Post date:** [31 August 2022 20:34 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/5 "2022-08-31T20:34:10Z")

</div>

I don't think this is a bug, but I'm less comfortable with it than @E1cid. There may also be more going on. In this version of @zenofmud's flow, the `function` node does what I would expect in JavaScript: the undefined flow variables are returned as `undefined`, the sum is `NaN`, and there is no error. The `change` node seems to ignore any property that is undefined, and JSONata behaves differently than JS. Everything may be working as intended, but the inconsistency is a bit off-putting.

```auto
[{"id":"1b34f2e69b481f3d","type":"inject","z":"edd7b753d67c3de6","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"55","payloadType":"num","x":190,"y":60,"wires":[["7c08c8263ebca986"]]},{"id":"7c08c8263ebca986","type":"change","z":"edd7b753d67c3de6","name":"","rules":[{"t":"set","p":"var1","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":210,"y":140,"wires":[["16f98cf758e70bcc","4204bdfb2b189e0f"]]},{"id":"92c935c39b9f84fb","type":"catch","z":"edd7b753d67c3de6","name":"","scope":null,"uncaught":false,"x":380,"y":60,"wires":[["7cc339226879bd18"]]},{"id":"7cc339226879bd18","type":"debug","z":"edd7b753d67c3de6","name":"debug 4","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":540,"y":60,"wires":[]},{"id":"4204bdfb2b189e0f","type":"change","z":"edd7b753d67c3de6","name":"change to add 3 flow variables","rules":[{"t":"set","p":"payload","pt":"msg","to":"$flowContext('var1')+$flowContext('var2')+$flowContext('var3')","tot":"jsonata"},{"t":"set","p":"var1","pt":"msg","to":"var1","tot":"flow"},{"t":"set","p":"var2","pt":"msg","to":"var2","tot":"flow"},{"t":"set","p":"var3","pt":"msg","to":"var3","tot":"flow"},{"t":"set","p":"test0","pt":"msg","to":"var1 + var2 + var3","tot":"jsonata"},{"t":"set","p":"test1","pt":"msg","to":"$sum([$flowContext('var1'),$flowContext('var2'),$flowContext('var3')])","tot":"jsonata"}],"action":"","property":"","from":"","to":"","reg":false,"x":450,"y":160,"wires":[["f672c0dbd3d4de96"]]},{"id":"16f98cf758e70bcc","type":"function","z":"edd7b753d67c3de6","name":"function to add 3 flow variables","func":"msg.var1 = flow.get('var1')\nmsg.var2 = flow.get('var2')\nmsg.var3 = flow.get('var3')\nmsg.payload = flow.get('var1') + flow.get('var2') + flow.get('var3')\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":450,"y":120,"wires":[["f672c0dbd3d4de96"]]},{"id":"f672c0dbd3d4de96","type":"debug","z":"edd7b753d67c3de6","name":"debug","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":670,"y":140,"wires":[]}]

```

---

<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:** [2 September 2022 13:59 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/6 "2022-09-02T13:59:20Z")

</div>

> [@drmibell](#):
>
> Everything may be working as intended, but the inconsistency is a bit off-putting.

I agree with everything working as intended. As for the inconsistency, this is not ours to question - it is what JSONata does as far as I can see.

For example,

If you add 55 and 2 undefined, you get nothing...  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/6/b/6becae3eaca033f6134ec8f185d4c7265b134cef.png)

If you sum 55 and 2 undefined, you get 55...  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/f/a/fae3d847450401d9a16ff64ede1686e7dea1afde.png)

And if you put the values in an array, you can see why `$sum(var1,var2,var3)` returns `[55]` ...  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/2/3/2344bd0464403882db8a0e35dd8b5cb06726e2c9.png)

* * *

The results are same in node-red...

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/0/c/0c32e6751be6f9325563c00df7aaf0563d90bdfc.png)

So to summarise, node-red is doing what JSONata intends as far as I can see.

---

<div class="post-metadata">

**Author:** ![zenofmud](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/zenofmud/32/316_2.png) [@zenofmud](https://discourse.nodered.org/u/zenofmud)\
**Post date:** [2 September 2022 14:08 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/7 "2022-09-02T14:08:48Z")

</div>

@Steve-Mcl the thing is that with the example I provide, there is no msg.payload in the output msg from the change node.

I guess this means that when using JSONata you better examine the results before trying to use it 🙁

---

<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:** [2 September 2022 14:59 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/8 "2022-09-02T14:59:09Z")

</div>

> [@zenofmud](#):
>
> the thing is that with the example I provide, there is no msg.payload in the output msg from the change node.

Yeah, I did see that Paul - to be clear, the JSONata outputs nothing (as in "not a `null`" / "not an `undefined`" - it literally doesn't output anything). This is how node-red currently represents that JSONata behaviour.

I'm not saying it should or shouldn't output a `payload: null` or `payload: undefined` or `payload: NaN` or even throw an error, just that doesnt and that is its current behaviour - and some users flows will now likely depend on that behaviour. Something that, if were to be changed, would only happen in a major Version release (next one is v4.0.0). If users feel strongly about this, then please raise an issue so that it is tracked. Nick may reject it but sitting here alone it will be missed.

---

<div class="post-metadata">

**Author:** ![drmibell](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/drmibell/32/8424_2.png) [@drmibell](https://discourse.nodered.org/u/drmibell)\
**Post date:** [2 September 2022 15:31 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/9 "2022-09-02T15:31:06Z")

</div>

> [@Steve-Mcl](#):
>
> this is not ours to question

I mentioned one thing that is strictly a NR (not JSONata) issue. The `function` and `change` nodes seem to treat undefined context variables differently.

```auto
[{"id":"f3402886d726ed8e","type":"inject","z":"edd7b753d67c3de6","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"55","payloadType":"num","x":190,"y":240,"wires":[["9a2f9e298ebfdb10"]]},{"id":"9a2f9e298ebfdb10","type":"change","z":"edd7b753d67c3de6","name":"","rules":[{"t":"set","p":"var1","pt":"flow","to":"payload","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":210,"y":300,"wires":[["a3cbfa87b1e424fe","85ebed23269f0e77"]]},{"id":"a3cbfa87b1e424fe","type":"function","z":"edd7b753d67c3de6","name":"function to get 3 flow variables","func":"msg.var1 = flow.get('var1')\nmsg.var2 = flow.get('var2')\nmsg.var3 = flow.get('var3')\n// msg.payload = flow.get('var1') + flow.get('var2') + flow.get('var3')\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":450,"y":280,"wires":[["9a2a484c67f51362"]]},{"id":"85ebed23269f0e77","type":"change","z":"edd7b753d67c3de6","name":"change to get 3 flow variables","rules":[{"t":"set","p":"payload","pt":"msg","to":"$flowContext('var1')+$flowContext('var2')+$flowContext('var3')","tot":"jsonata"},{"t":"set","p":"var1","pt":"msg","to":"var1","tot":"flow"},{"t":"set","p":"var2","pt":"msg","to":"var2","tot":"flow"},{"t":"set","p":"var3","pt":"msg","to":"var3","tot":"flow"}],"action":"","property":"","from":"","to":"","reg":false,"x":450,"y":320,"wires":[["9a2a484c67f51362"]]},{"id":"9a2a484c67f51362","type":"debug","z":"edd7b753d67c3de6","name":"debug","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":670,"y":300,"wires":[]}]

```

---

<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:** [2 September 2022 15:44 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/10 "2022-09-02T15:44:08Z")

</div>

> [@drmibell](#):
>
> The `function` and `change` nodes seem to treat undefined context variables differently

I disagree. JSONata is NOT returning a value and "no value" is represented by "no property" in JS. "No property" is different to a `property: null`, `property: undefined`, etc etc

Just because the function node does what it does (which btw is because you assigned an `undefined` to a property of an `object` [aka the `msg`]) does not mean that is how the JSONata in a change MUST work when faced with an undefined value.

Look at the array example...

> [@Steve-Mcl](#):
>
> ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/2/3/2344bd0464403882db8a0e35dd8b5cb06726e2c9.png)

... its like the values dont exist (as in not a `null`, not an `undefined`).

Try for yourself in the [playground](https://www.stedi.com/jsonata/playground?statev2=eJyLjlYqzi8tSk5V0lFKrSgoSi0uzszPA3ISawxqDIF0dUyegkKMUllikWGMkpWCgqlpTF4tUDwaJKIDJIxAhHEsUCi%2FxqjGuMZEKVZHyVQpFgAQ8xtI)

* * *

Even after all that 👆 it changes nothing to what I already said...

> [@Steve-Mcl](#):
>
> I'm not saying it should or shouldn't output a `payload: null` or `payload: undefined` or `payload: NaN` or even throw an error, just that doesnt and that is its current behaviour - and some users flows will now likely depend on that behaviour. Something that, if were to be changed, would only happen in a major Version release (next one is v4.0.0).

---

<div class="post-metadata">

**Author:** ![drmibell](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/drmibell/32/8424_2.png) [@drmibell](https://discourse.nodered.org/u/drmibell)\
**Post date:** [2 September 2022 15:57 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/11 "2022-09-02T15:57:13Z")

</div>

> [@Steve-Mcl](#):
>
> Even after all that 👆 it changes nothing to what I already said...

I understand and agree with everything you said, but I am now more confused. My example has nothing to do with JSONata. I don't understand why

```auto
msg.var2 = flow.get('var2')

```

in a `function` node should return `undefined` while

 ![Untitled](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/2/72fc8fc47ffc966f77218571a96732174ba8e603.jpeg)

in a `change` node returns "no property."

---

<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:** [2 September 2022 16:11 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/12 "2022-09-02T16:11:35Z")

</div>

> [@drmibell](#):
>
> in a `function` node should return `undefined` while
> 
> ![Untitled](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/2/72fc8fc47ffc966f77218571a96732174ba8e603.jpeg)
> 
> in a `change` node returns "no property."

Sorry Mike, I missed that detail.

> [@drmibell](#):
>
> ```auto
> msg.var2 = flow.get('var2')
> 
> ```
> 
> in a `function` node should return `undefined`

The behaviour (in a function node) is absolutely correct and as you demonstrate works as designed.

> [@drmibell](#):
>
> ![Untitled](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/2/72fc8fc47ffc966f77218571a96732174ba8e603.jpeg)
> 
> in a `change` node returns "no property."

This behaviour is debateable for sure but I am faily certain I know why this one does this (this time tho, I am not certain it is right or hasn't changed). Does anyone know if this behaviour has changed between V1 ~ v2 ~ v3?

---

<div class="post-metadata">

**Author:** ![zenofmud](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/zenofmud/32/316_2.png) [@zenofmud](https://discourse.nodered.org/u/zenofmud)\
**Post date:** [2 September 2022 17:53 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/13 "2022-09-02T17:53:05Z")

</div>

I'll test it on v3.0.2, v2.2.2 and v1.3.5

So I ran the flow on each of the versions - It looks like the same thing occurs in all three versions - I renamed the inject node with the version number for each run.  
NR v1.3.5

 ![Screen Shot 2022-09-02 at 3.39.23 PM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/4/6/461da57b05020bc05f813c74cffecb8eab7ed4d6.png)

NR v2.2.2

 ![Screen Shot 2022-09-02 at 3.54.41 PM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/2/c/2c5c50b29f1cb55a0d4982d759906db23a5ea95e.png)

NR v3.0.2

 ![Screen Shot 2022-09-02 at 4.12.37 PM](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/3/3/33c1636d1a0d68a03645e1e93e3d044cefbf974f.png)

---

<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:** [1 November 2022 17:54 UTC](https://discourse.nodered.org/t/bug-using-change-node-jsonata-to-add-non-existing-flow-global-variables-generates-no-error/67148/14 "2022-11-01T17:54:01Z")

</div>

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