# Message structure checking not working as I thought

**URL:** <https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817>\
**Category:** General\
**Created:** [26 October 2020 09:41 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817 "2020-10-26T09:41:37Z")\
**Posts on this page:** 16\
**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:** [26 October 2020 09:41 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/1 "2020-10-26T09:41:37Z")

</div>

Ok, sorry, but this is confusing me.

I've recently been down the message structure trip and have learnt a couple of things.

So, I get a message from `openweathermap` node.

The rain fall is given in the message as: `msg.data.rain["1h"]`  
Well, that's what is seems like when it is raining in the place.

So it has now raised the problem/question if there is no rain.

That part of the message doesn't exist.

So I wrote this:

```auto
node.warn(msg.data.rain["1h"]);

var x = msg.data.rain["1h"];

node.warn(x);

```

(Just to be sure)

Nothing.

No `undefined` messages.... No messages at all.

Why?

If that part of the message doesn't exist, why am I not getting an `undefined` message from 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:** [26 October 2020 09:46 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/2 "2020-10-26T09:46:37Z")

</div>

> [@Trying\_to\_learn](#):
>
> If that part of the message doesn't exist, why am I not getting an `undefined` message from it?

Does the `msg.data` part exist?  
Does the `msg.data.rain` part exist?

are you getting an error?

Perhaps you should check before accessing...

```JavaScript

// disable this to avoid an error when data or data.rain are undefined
// node.warn(msg.data.rain["1h"]);  

//if msg.data && msg.data.rain are SOMETHING, 
// then set x to msg.data.rain["1h"]  
// otherwise set x to null
var x = (msg.data && msg.data.rain) ? msg.data.rain["1h"] : null;

node.warn(x);

```

#### EDIT

A tip for when you use `node.warn` - it can be dificult to see what the node.warn is warning you about when its just a number. Also, when its an object, you dont get to expand it etc.

When doing node.warn, I always do this....

```auto
node.warn(["rain value",x])

```

And you can even do this....

```javascript
node.warn( ["check the msg object value for msg.data.rain.1h should be same as x", msg, x] );

```

... and see both the msg and the item of interest in the same `warn` message at the same time (no more guessing which `msg` was used to get `x`)

---

<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:** [26 October 2020 10:00 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/3 "2020-10-26T10:00:56Z")

</div>

If there is no rain, `msg.data.rain` doesn't exist.

So I'm not sure that would work.

Got this working though.

```auto
if (msg.data.rain === undefined)
{
    msg.payload = "clear";
} else
{
    msg.payload = msg.data.rain["1h"];
}
return msg;

```

---

<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:** [26 October 2020 10:07 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/4 "2020-10-26T10:07:20Z")

</div>

Sorry Steve,

I got a bit confused. But thanks for helping with checking the structure.

I'm guessing that the `[1]` part was not helping. So checking that the part before that existed seems to do the trick.

---

<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:** [26 October 2020 10:07 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/5 "2020-10-26T10:07:36Z")

</div>

> [@Trying\_to\_learn](#):
>
> If there is no rain, `msg.data.rain` doesn't exist.

Yeah - and?

```javascript
//if msg.data && msg.data.rain are SOMETHING, 
// then set x to msg.data.rain["1h"]  
// otherwise set x to null
var x = (msg.data && msg.data.rain) ? msg.data.rain["1h"] : null;

```

^ do you not understand what that is doing? What happens is...

- if `msg.data` is `undefined` - x gets set to `null` (or "clear" or whatever you want)
- if `msg.data` is present BUT `msg.data.rain` is undefined - x gets set to `null` (or "clear" or whatever you want)
- if `msg.data` is present AND `msg.data.rain` is present - x gets set to `msg.data.rain["1h"]`

> [@Trying\_to\_learn](#):
>
> So I'm not sure that would work.

Yes it will - you didnt try did you!

  
  

> [@Trying\_to\_learn](#):
>
> Got this working though.
> 
> ```javascript
> if (msg.data.rain === undefined)
> {
> msg.payload = "clear";
> } else
> {
> msg.payload = msg.data.rain["1h"];
> }
> return msg;
> 
> ```

And what if msg.data is empty? You WILL get an error in your version!

---

<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:** [26 October 2020 10:10 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/6 "2020-10-26T10:10:09Z")

</div>

> [@Steve-Mcl](#):
>
> ```auto
> var x = (msg.data && msg.data.rain) ? msg.data.rain["1h"] : null;
> 
> ```
> 
> ^ do you not understand what that is doing?

No, I have never been good with that sort of stuff. So, no: I didn't try it. I don't understand how it works.

I may have to sit down and learn it one day, but it really just blows my socks off with the iterations (or what ever it is called.)

Back in 1980 I may have understood it but only if it was written in BASIC.

---

<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:** [26 October 2020 10:12 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/7 "2020-10-26T10:12:37Z")

</div>

> [@Steve-Mcl](#):
>
> And what if msg.data is empty?

I'm guessing that if it exists, there will be a value. If there is no value, it is undefined.  
As I have got two places showing rain and no rain and where there is no rain, the path/structure doesn't exist.

**and** I used `msg.data.rain`.... not just `msg.data`.

---

<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:** [26 October 2020 10:16 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/8 "2020-10-26T10:16:57Z")

</div>

```auto
var x = (msg.data && msg.data.rain) ? msg.data.rain["1h"] : null;

```

2 constructs exist her...

1. ternary operator : `something == a_value ? true_value: otherwise_value`  
or in english : if `something equals a_value` return `true_value` otherwise return `otherwise_value`

2. short circuits : (msg.data && msg.data.rain)

So again...

```auto
var x = (msg.data && msg.data.rain) ? msg.data.rain["1h"] : "clear";
// if msg.data is undefined/null/false - set x to "clear" - STOP 
// if msg.data.rain is undefined/null/false - set x to "clear" - STOP 
// if msg.data && msg.data.rain are SOMETHING set x to msg.data.rain["1h"]  

```

---

<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:** [26 October 2020 10:20 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/9 "2020-10-26T10:20:00Z")

</div>

> [@Trying\_to\_learn](#):
>
> > [@Steve-Mcl](#):
> >
> > And what if msg.data is empty?
> 
> I'm guessing that if it exists, there will be a value. If there is no value, it is undefined.

Andrew - guessing is why you have so many problems.

In your version, if `msg.data` is undefined - your function node will throw an error.

why? - because you try to evaluate msg.data.rain

look at the first line of your "working" function...

```auto
if (msg.data.rain === undefined)

```

This will **instantly** throw an error if msg.data is missing.

where as the version i provided will NOT throw an error.

* * *

Any how, you crack on asking for answers then ignore them.

---

<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:** [26 October 2020 10:21 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/10 "2020-10-26T10:21:12Z")

</div>

I pull the rain data like this if undefined it returns 0

```auto
[{"id":"ffc02d8f.5c58c8","type":"inject","z":"8d22ae29.7df6d","name":"","props":[{"p":"payload.ChargeState","v":"11","vt":"num"},{"p":"msg.data","v":"{\"coord\":{\"lon\":0.28,\"lat\":50.77},\"weather\":[{\"id\":500,\"main\":\"Rain\",\"description\":\"light rain\",\"icon\":\"10d\"}],\"base\":\"stations\",\"main\":{\"temp\":285.29,\"feels_like\":283.19,\"temp_min\":284.26,\"temp_max\":285.93,\"pressure\":1000,\"humidity\":81},\"visibility\":10000,\"wind\":{\"speed\":2.68,\"deg\":279,\"gust\":7.15},\"rain\":{\"1h\":0.44},\"clouds\":{\"all\":87},\"dt\":1603706880,\"sys\":{\"type\":3,\"id\":2012607,\"country\":\"GB\",\"sunrise\":1603694438,\"sunset\":1603730684},\"timezone\":0,\"id\":2650497,\"name\":\"Eastbourne\",\"cod\":200}","vt":"json"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","x":110,"y":2140,"wires":[["1d751194.60f8de"]]},{"id":"1632356d.a64dc3","type":"inject","z":"8d22ae29.7df6d","name":"","props":[{"p":"payload.ChargeState","v":"11","vt":"num"},{"p":"msg.data","v":"{\"coord\":{\"lon\":0.28,\"lat\":50.77},\"weather\":[{\"id\":500,\"main\":\"Rain\",\"description\":\"light rain\",\"icon\":\"10d\"}],\"base\":\"stations\",\"main\":{\"temp\":285.29,\"feels_like\":283.19,\"temp_min\":284.26,\"temp_max\":285.93,\"pressure\":1000,\"humidity\":81},\"visibility\":10000,\"wind\":{\"speed\":2.68,\"deg\":279,\"gust\":7.15},\"clouds\":{\"all\":87},\"dt\":1603706880,\"sys\":{\"type\":3,\"id\":2012607,\"country\":\"GB\",\"sunrise\":1603694438,\"sunset\":1603730684},\"timezone\":0,\"id\":2650497,\"name\":\"Eastbourne\",\"cod\":200}","vt":"json"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","x":110,"y":2200,"wires":[["1d751194.60f8de"]]},{"id":"1d751194.60f8de","type":"function","z":"8d22ae29.7df6d","name":"","func":"msg.rain = msg.data.rain || {\"1h\":0};\nmsg.rain = Object.values(msg.rain)[0];\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":280,"y":2180,"wires":[["49952583.65b3fc"]]},{"id":"49952583.65b3fc","type":"debug","z":"8d22ae29.7df6d","name":"","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"true","targetType":"full","statusVal":"","statusType":"auto","x":470,"y":2160,"wires":[]}]

```

---

<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:** [26 October 2020 10:27 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/11 "2020-10-26T10:27:56Z")

</div>

Ok, I used the wrong word.

I have seen two places. When one place has rain, the _path_ in the message payload exists.  
If there is no rain, the _path_ in the message payload doesn't.

So I _guess_ that what I said is true: if there is rain, the path exists, and if there is no rain, the path doesn't.

By my original inclusion of the `["1"]` messed up the checking.  
Dunno why.  
But if I only check the path to `msg.data.rain` and not `msg.data.rain["1"]` the check works.

> [@Steve-Mcl](#):
>
> if `msg.data` is undefined

I **know** in all my examples it was `msg.data.rain` and not `msg.data`.  
So the rest of your reply is ..... _void_?

`msg.data` always exists in all tests / messages received from the node.  
It is just `msg.data.rain` may not.

It isn't that I ignore answers.  
It is more I ask a question and don't sit here/_there_ expecting an answer.  
I try to nut it out in the mean time myself.

I sometimes need to ask it on the forum to help myself get my head around the problem.  
I'm sure I have mentioned this and declared it many times.

Sorry. It may not be a _nice_ way, but it is the only way I seem to be able to get things done.

---

<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:** [26 October 2020 10:29 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/12 "2020-10-26T10:29:02Z")

</div>

Yes that is fair enough. But I wanted to return `Clear` so in the field which says "Rain" it displays "Clear".

---

<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:** [26 October 2020 10:29 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/13 "2020-10-26T10:29:39Z")

</div>

change value from 0 to clear in function node.

```auto
msg.rain = msg.data.rain || {"1h":"Clear"};
msg.rain = Object.values(msg.rain)[0];
return msg;

```

---

<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:** [26 October 2020 10:30 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/14 "2020-10-26T10:30:12Z")

</div>

> [@Trying\_to\_learn](#):
>
> `msg.data` always exists in all tests / messages received from the node.  
> It is just `msg.data.rain` may not.

And that statement is why you have bugs as far as I am concerned.

Programmers should NEVER assume anything.

---

<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:** [26 October 2020 10:31 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/15 "2020-10-26T10:31:54Z")

</div>

I can't prove that is true.  
I am not that smart a programmer.  
I admit that.

I can only say that all the messages comply (obey?) this theory.

So until it isn't disproved I can't see why it can't be _true_ at this point.

---

<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:** [9 November 2020 10:31 UTC](https://discourse.nodered.org/t/message-structure-checking-not-working-as-i-thought/34817/16 "2020-11-09T10:31:54Z")

</div>

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