# Catching errors in \`subflow\` - more help please

**URL:** <https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746>\
**Category:** General\
**Created:** [17 June 2024 05:04 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746 "2024-06-17T05:04:53Z")\
**Posts on this page:** 9\
**Page:** 1

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [17 June 2024 05:04 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/1 "2024-06-17T05:04:53Z")

</div>

I did a bit of digging and it paid off.

(extract from code used:)

```auto
if (typeof msg.delay === "undefined")
{
    const id = env.get("NR_NODE_PATH");
    const ids = id.split("/");
    const errr = `msg.delay not set in message going into ${ids[1]}`;
    node.error(errr, msg);
    msg.source = ids[1];
    return;
}

```

Which is all well and good for THAT instance and THAT error.

So it now begs the question to me:  
How do I `catch` errors in a subflow and pass on the error to the _parent_ flow so the \*parent flow's error message points to the subflow node.

I'm not sure how it will work with this node already managing it's own errors.

Could I just negate this part and handle all errors with the `catch` node in the subflow?  
Would make it easier.  
🙂

I've kinda done it, but the formatting is not the best and I just get a message with the dummy error message and the node's number all in one line.

How would I format it so the node number is per _real_ error messages?  
And maybe pass on the whole error message too?  
(Trying ITMT)

# Update:

This is a test flow I made to check.

Thoughts?

```auto
[{"id":"089874d72f82b238","type":"subflow","name":"Error handler for subflows","info":"2024 06 17\n==========\n\nBasic overview.\n`TEST node` causes an error.\n(any input)\n\n`Upsend error message` relays the\nerror message to the parent flow.\n`error.source` -> subflow with error\n`_error.source.name` -> name of node that\ncaused the error.\n`_error.message` -> the error message\n\nSuggestion:\n-----------\nThe `catch` node should only catch\nerrors from `function` nodes.\n","category":"","in":[{"x":230,"y":70,"wires":[{"id":"18bb902b0b89f912"}]}],"out":[{"x":360,"y":190,"wires":[{"id":"830e5e8780badf3b","port":0}]}],"env":[],"meta":{},"color":"#DDAA99"},{"id":"18bb902b0b89f912","type":"function","z":"089874d72f82b238","name":"TEST node","func":"node.error(\"Error\",msg)","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":410,"y":70,"wires":[[]]},{"id":"830e5e8780badf3b","type":"catch","z":"089874d72f82b238","name":"","scope":["18bb902b0b89f912"],"uncaught":false,"x":200,"y":190,"wires":[["06b515199b7eb047"]]},{"id":"06b515199b7eb047","type":"function","z":"089874d72f82b238","name":"Upsend error message","func":"const id = env.get(\"NR_NODE_PATH\");\nconst ids = id.split(\"/\");\nconst errr = `Something went wrong in subflow (See source number below).\\nopen the _error.source object (below) to get more details`;\nmsg.source = ids[1];\nnode.error(errr, msg);\n \n","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":440,"y":240,"wires":[[]]},{"id":"52cc9476d774b429","type":"subflow:089874d72f82b238","z":"7e987ddf260bdf0d","name":"","x":420,"y":3410,"wires":[["58bd64507cef17b7"]]},{"id":"897d573b21452c75","type":"inject","z":"7e987ddf260bdf0d","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"","payloadType":"date","x":170,"y":3410,"wires":[["52cc9476d774b429"]]},{"id":"58bd64507cef17b7","type":"debug","z":"7e987ddf260bdf0d","name":"Used for testing.","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":860,"y":3410,"wires":[]},{"id":"a28a91a006a4fee5","type":"catch","z":"7e987ddf260bdf0d","name":"","scope":["52cc9476d774b429"],"uncaught":false,"x":360,"y":3510,"wires":[["2257c395145111bb","ffcfe59eeec7ec81"]]},{"id":"2257c395145111bb","type":"debug","z":"7e987ddf260bdf0d","name":"Ok error message","active":false,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":870,"y":3450,"wires":[]},{"id":"ffcfe59eeec7ec81","type":"change","z":"7e987ddf260bdf0d","name":"","rules":[{"t":"move","p":"_error.source","pt":"msg","to":"error.source","tot":"msg"}],"action":"","property":"","from":"","to":"","reg":false,"x":600,"y":3510,"wires":[["2acd17e7327bb6bc"]]},{"id":"2acd17e7327bb6bc","type":"debug","z":"7e987ddf260bdf0d","name":"Better error message","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":880,"y":3510,"wires":[]}]

```

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [17 June 2024 09:43 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/2 "2024-06-17T09:43:35Z")

</div>

It seems to me that if an error occurs in a subflow it's useful for that node to raise an error message in the debug pane. However it gives no indication of which flow called the subflow and caused the error.

I don't use subflows much but if I did I would set a policy of always testing for msg.error in the subflow output.

 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/b/2/b22847ef159b4c5b866421fb12143a5505c5cc15.png)

```auto
[{"id":"35e0cbf557489b94","type":"subflow","name":"Convert oz to g","info":"","category":"","in":[{"x":280,"y":80,"wires":[{"id":"35b905044e421edf"}]}],"out":[{"x":520,"y":80,"wires":[{"id":"35b905044e421edf","port":0}]}],"env":[],"meta":{},"color":"#DDAA99"},{"id":"35b905044e421edf","type":"function","z":"35e0cbf557489b94","name":"function 1","func":"if (typeof msg.payload != \"number\") {\n msg.error = \"No valid ounces value received\"\n node.error(\"Bad input data\")\n}\nelse {\n msg.payload = msg.payload * 28.34949\n}\nreturn msg;\n","outputs":1,"timeout":0,"noerr":0,"initialize":"","finalize":"","libs":[],"x":400,"y":80,"wires":[[]]},{"id":"8c20323b911f6b0e","type":"inject","z":"a847a62177aa3eb7","name":"Good data - number","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"16","payloadType":"num","x":130,"y":80,"wires":[["07f0f1c64feada9a"]]},{"id":"07f0f1c64feada9a","type":"subflow:35e0cbf557489b94","z":"a847a62177aa3eb7","name":"","x":340,"y":100,"wires":[["a4e6ab74fc44acb2"]]},{"id":"5f5172ff34f848ef","type":"debug","z":"a847a62177aa3eb7","name":"Good conversion - Grams","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":730,"y":80,"wires":[]},{"id":"1d45b002d145855a","type":"inject","z":"a847a62177aa3eb7","name":"Bad data - string","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"16","payloadType":"str","x":120,"y":120,"wires":[["07f0f1c64feada9a"]]},{"id":"a4e6ab74fc44acb2","type":"switch","z":"a847a62177aa3eb7","name":"msg.error?","property":"error","propertyType":"msg","rules":[{"t":"null"},{"t":"else"}],"checkall":"true","repair":false,"outputs":2,"x":510,"y":100,"wires":[["5f5172ff34f848ef"],["adab2f4de69d3a1c"]]},{"id":"adab2f4de69d3a1c","type":"debug","z":"a847a62177aa3eb7","name":"Error message","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"error","targetType":"msg","statusVal":"","statusType":"auto","x":700,"y":120,"wires":[]}]

```

This is the output if I pass a valid number to the subflow  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/5/9/59d0eb56277e767db09dafb6e7d00a22ac1b7587.png)

And here is the result of passing a string  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/0/7/0745bb49e058d58d46d3f60628ff8694ed59f2db.png)

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [17 June 2024 09:45 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/3 "2024-06-17T09:45:56Z")

</div>

Thanks.

That's an interesting approach to it.

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [17 June 2024 09:54 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/4 "2024-06-17T09:54:24Z")

</div>

In fact a subflow can have two outputs, one for good data, one for error notifications. So I could dispense with the switch node  
 ![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/7/2/727b0977a020347ea341de48d7b99d22b5540e7f.png)

![image](https://us1.discourse-cdn.com/flex026/uploads/nodered/original/3X/4/c/4ce0adebe8ddacec4851e9ec0a61374d6326e5e6.png)

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [17 June 2024 09:55 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/5 "2024-06-17T09:55:33Z")

</div>

So the second output is just the direct output from the internal `catch` node?

I'm only saying/asking about it because I have `error catching routines` on all my flows - in the production machines - to help handle errors.

---

<div class="post-metadata">

**Author:** ![jbudd](https://avatars.discourse-cdn.com/v4/letter/j/5f8ce5/32.png) [@jbudd](https://discourse.nodered.org/u/jbudd)\
**Post date:** [17 June 2024 10:09 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/6 "2024-06-17T10:09:04Z")

</div>

Well not in that example.  
I don't have a catch node because I'm happy to see an error message in the debug.  
After all an error occurred; I see no value in making it less obvious.

Instead the function in my simple subflow has two outputs which are directed to the relevant output from the subflow.

I think this approach relies on the fact that a node.error() call does not halt further processing in a function node.

Generally speaking my flows are not as complex as yours. My ideas might well be inappropriate for your production algorithms.

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [17 June 2024 10:11 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/7 "2024-06-17T10:11:56Z")

</div>

Ok, thanks.

We may be on _different pages_ on the workings. But that's ok.

I'm trying to get a bigger picture of how to do this so if it is a _complicated_ `subflow` and an error happens, I can get the `subflow` name/number - to identify it from all other instances of it - and the actual error the `subflow` created.

I think my way the original error is held in the `_error` part of the message.

---

<div class="post-metadata">

**Author:** ![Trying\_to\_learn](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/trying_to_learn/32/28400_2.png) [@Trying\_to\_learn](https://discourse.nodered.org/u/Trying_to_learn)\
**Post date:** [17 June 2024 10:12 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/8 "2024-06-17T10:12:42Z")

</div>

Thanks though. It is sometimes good to look at it from a different point of view.

And yes, alas my flows are a bit _scary_)

---

<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:** [15 September 2024 10:13 UTC](https://discourse.nodered.org/t/catching-errors-in-subflow-more-help-please/88746/9 "2024-09-15T10:13:34Z")

</div>

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