# Trying to understand - - TypeError: Cannot read property 'length' of undefined
**URL:** https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168
**Category:** General
**Created:** [25 August 2021 16:17 UTC](https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168 "2021-08-25T16:17:21Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@RaptorUK](https://discourse.nodered.org/u/RaptorUK)
#### Post date: [25 August 2021 16:17 UTC](https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168/1 "2021-08-25T16:17:21Z")
I've ben trying to create a set of Yes/No type buttons which after a set timeout will default to "No" . . . I've managed to get it working but lost a lot of time to the following error: _ **TypeError: Cannot read property 'length' of undefined** _
I've gotten around this but would like to understand why the error was being generated . . .
I have some test nodes to illustrate the issue:
Failing nodes:
```auto
[{"id":"acad1cef.8f8a3","type":"inject","z":"b7065b03.85e128","name":"enable","props":[{"p":"enabled","v":"true","vt":"bool"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payloadType":"str","x":310,"y":1240,"wires":[["9c356d1d.26da9"]]},{"id":"9c356d1d.26da9","type":"function","z":"b7065b03.85e128","name":"","func":"var print = { payload: msg.payload.length };\n\nprint = msg;\n\nreturn print;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":470,"y":1240,"wires":[["2db2248d.8c444c"]]},{"id":"2db2248d.8c444c","type":"debug","z":"b7065b03.85e128","name":"msg","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":630,"y":1240,"wires":[]}]
```
Not failing nodes:
```auto
[{"id":"acad1cef.8f8a3","type":"inject","z":"b7065b03.85e128","name":"enable","props":[{"p":"payload"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"true","payloadType":"bool","x":310,"y":1240,"wires":[["9c356d1d.26da9"]]},{"id":"9c356d1d.26da9","type":"function","z":"b7065b03.85e128","name":"","func":"var print = { payload: msg.payload.length };\n\nprint = msg;\n\nreturn print;","outputs":1,"noerr":0,"initialize":"","finalize":"","libs":[],"x":470,"y":1240,"wires":[["2db2248d.8c444c"]]},{"id":"2db2248d.8c444c","type":"debug","z":"b7065b03.85e128","name":"msg","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":630,"y":1240,"wires":[]}]
```
The difference is that the failing node injects _ **msg.enabled = true** _ the not failing node injects _ **msg.payload = true** _
---
### Author:  [@hotNipi](https://discourse.nodered.org/u/hotNipi)
#### Post date: [25 August 2021 16:35 UTC](https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168/2 "2021-08-25T16:35:18Z")
For failing case the `inject` node does not send `payload` property (msg has only `enabled` property)
But in the following function you are trying to read `payload.length`. If property of object does not exist, you can't examine any part of it.
In this case you cant ask the `length` of `msg.payload` because `msg` does not have `payload`
---
### Author:  [@RaptorUK](https://discourse.nodered.org/u/RaptorUK)
#### Post date: [25 August 2021 16:44 UTC](https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168/3 "2021-08-25T16:44:06Z")
> [@hotNipi](#):
>
> For failing case the `inject` node does not send `payload` property (msg has only `enabled` property)
> But in the following function you are trying to read `payload.length` .
Ahh, I see . . . I assumed that;
```auto
var print = { payload: msg.payload.length },
```
was a kind of variable type or prototype, I didn't realise it would actually look for msg.payload.length
Thanks for the explanation. Every day is a school day 👍
---
### Author:  [@system](https://discourse.nodered.org/u/system)
#### Post date: [8 September 2021 16:44 UTC](https://discourse.nodered.org/t/trying-to-understand-typeerror-cannot-read-property-length-of-undefined/50168/4 "2021-09-08T16:44:51Z")
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