# Message queue node that can be indexed

**URL:** <https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555>\
**Category:** General\
**Created:** [19 January 2020 01:23 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555 "2020-01-19T01:23:00Z")\
**Posts on this page:** 14\
**Page:** 2

<div class="post-metadata">

**Author:** ![dceejay](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/dceejay/32/38_2.png) [@dceejay](https://discourse.nodered.org/u/dceejay)\
**Post date:** [20 January 2020 08:49 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/21 "2020-01-20T08:49:42Z")

</div>

Well you first should try to get it from context... which I think you are doing.....

```auto
var queue_array = flow.get("queue") // I'm guessing this checks if the array exists.

```

but then at the end you have to save it back to context... otherwise next time it won't be there...

---

<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:** [20 January 2020 08:53 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/22 "2020-01-20T08:53:49Z")

</div>

Woo - hoo!

I think that was lucky of me as I just worked that out - I think.

I added this to the end of the block:  
`flow.set('queue',queue_array);`

But the output I am seeing is not understandable.

Oh, after looking a bit harder, I think I get it.

I'll apply it to the other node I am actually using and see if it helps.

Hmmmmm....  
Ok, I think I have one part of it working.

But now I can't **wipe** the array when I want to. I have _accidentally_ saved 15 entries and can't wipe them.

I thought the command would be `queue_array = [];` because that was what I had before when it kept getting wiped.

This is a snip-it of the code:

```auto
    if (msg.payload == "WIPE ALL")
    {
        // Wipe the whole array
    node.warn("Initialising array");
    queue_array = [];
    return;

```

This is what is telling me the array isn't being wiped.

```auto
let index = context.get('SIZE') || 0; // I hope this part works. (See below)
node.warn("Index size from context " + index);
index = queue_array.length; // This should get the *length* of the array.
node.warn("Index size from array " + index);

```

I see `0` then for the second line I see `15`.

So I am still missing something.

---

<div class="post-metadata">

**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [20 January 2020 09:36 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/23 "2020-01-20T09:36:09Z")

</div>

> [@Trying\_to\_learn](#):
>
> The `queue.pop( )` isn't covered in the link supplied about JS arrays. The only `pop` is for `JS popup` which is a popup message.

Pop is covered in the link that I gave. Just after `map` and before `push`.

> [@Trying\_to\_learn](#):
>
> This is what is telling me the array isn't being wiped.

You didn't write it back again so you didn't save the change.

---

<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:** [20 January 2020 09:38 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/24 "2020-01-20T09:38:49Z")

</div>

D'oh! Yeah. Silly me.  
I really must make idiots look smart.

---

<div class="post-metadata">

**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [20 January 2020 09:42 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/25 "2020-01-20T09:42:22Z")

</div>

You have some other logic issues too. As your code stands, you will never have a `next` will you? That's because you are adding to the queue after your other logic, I think that you need to add to it first?

---

<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:** [20 January 2020 10:14 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/26 "2020-01-20T10:14:26Z")

</div>

> [@TotallyInformation](#):
>
> As your code stands, you will never have a `next` will you?

True.  
The _idea_ is that things are put in the array.  
As they are put in, the only one I can really use is the _previous_ one.

But 😉

I scroll back a few entries and _what ever_. I may want to go to the _next_ entry too.

I'm working on it. Found quite a few problems with how the pointers are kept, etc.

Be Back Soon.

---

<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:** [20 January 2020 10:38 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/27 "2020-01-20T10:38:00Z")

</div>

Ok, I'm stuck.

`node.warn("Next entry " + i+1);`

Doesn't work.

I get `11` if i = `1`.

Is there a way - without introducing a new variable to get it to show i+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:** [20 January 2020 10:51 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/28 "2020-01-20T10:51:53Z")

</div>

This flow works - as best I can tell.

The node counters are NOT zero counting which I think helps with seeing which message you are viewing.

Could you help me with a more tidy way with the variable `j` in the scheme of things.

That doesn't mean directly you. But more a general request for help.  
Sorry the main `function` node still has a bit of old stuff in it.

That's the node with the `j` variable in it.  
The node shows how many entries in the array. NOT zero counting.  
So as the node shows the index number, I wanted it to also be non-zero counting.

Found a couple of spelling mistakes.

```auto
[{"id":"8e458e68.2f8d88","type":"function","z":"184dc884.7aba5f","name":"Array","func":"//\nvar output = \"\"; // This is what returns the indexed value.\nvar i = context.get('pointer') || 0;\nvar j = 0;\nvar queue_array = flow.get(\"queue\") // I'm guessing this checks if the array exists.\nif (!Array.isArray(queue_array))\n{\n // If not, set up array.\n node.warn(\"Initialising array\");\n queue_array = [];\n flow.set('queue',queue_array);\n node.warn(\"Array set up.\");\n}\n\nsize = queue_array.length;\n\nif (msg.topic == \"CONTROL\")\n{\n // Stuff to be done with array.\n if (msg.payload == \"NEXT\")\n {\n // Display next item\n i = i + 1;\n j = i + 1;\n node.warn(\"Next entry \" + j);\n output = queue_array[i];\n msg.payload = output;\n context.set('pointer',i); // Save the value.\n node.status(size + \" \" + j);\n return msg;\n } else\n if (msg.payload == \"PREVIOUS\")\n {\n // Display previous item\n i = i - 1;\n j = i + 1;\n node.warn(\"Previous entry \" + j);\n output = queue_array[i];\n msg.payload = output;\n context.set('pointer',i); // Save the value.\n node.status(size + \" \" + j);\n return msg;\n } else\n if (msg.payload == \"WIPE\")\n {\n // Delete this item\n } else\n if (msg.payload == \"WIPE ALL\")\n {\n // Wipe the whole array\n node.warn(\"Initialising array\");\n queue_array = [];\n flow.set('queue',queue_array);\n node.warn(\"Array Wiped.\");\n return;\n }\n}\n\nnode.warn(\"saving data to array\");\n\nqueue_array.push(msg.payload);\n\nsize = queue_array.length;\n\ncontext.set('pointer',i); // Save the value - for what ever reason.\n\nflow.set('queue',queue_array);\nnode.status(size + \" \" + pointer);\n\nreturn;\n","outputs":1,"noerr":0,"x":490,"y":1320,"wires":[["e09fc19c.cf203"]]},{"id":"c0ef557b.139f1","type":"template","z":"184dc884.7aba5f","name":"","field":"payload","fieldType":"msg","format":"handlebars","syntax":"mustache","template":"Message {{payload}}","output":"str","x":230,"y":1280,"wires":[["8e458e68.2f8d88","fcb9dca0.971b5"]]},{"id":"e09fc19c.cf203","type":"debug","z":"184dc884.7aba5f","name":"Index result","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":650,"y":1320,"wires":[]},{"id":"c4bbdffc.81ab78","type":"inject","z":"184dc884.7aba5f","name":"Next","topic":"CONTROL","payload":"NEXT","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":240,"y":1360,"wires":[["8e458e68.2f8d88"]]},{"id":"16235d1e.a6c2db","type":"inject","z":"184dc884.7aba5f","name":"Previous","topic":"CONTROL","payload":"PREVIOUS","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":230,"y":1390,"wires":[["8e458e68.2f8d88"]]},{"id":"8d565471.b8f5a","type":"inject","z":"184dc884.7aba5f","name":"Wipe All","topic":"CONTROL","payload":"WIPE ALL","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":230,"y":1470,"wires":[["8e458e68.2f8d88"]]},{"id":"bb6554dd.38b188","type":"inject","z":"184dc884.7aba5f","name":"Wipe","topic":"CONTROL","payload":"WIPE","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":240,"y":1440,"wires":[["8e458e68.2f8d88"]]},{"id":"26162964.640a16","type":"random","z":"184dc884.7aba5f","name":"Random number","low":"1","high":"10","inte":"true","property":"payload","x":200,"y":1250,"wires":[["c0ef557b.139f1"]]},{"id":"fcb9dca0.971b5","type":"debug","z":"184dc884.7aba5f","name":"History","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","x":500,"y":1230,"wires":[]},{"id":"638c9635.68a788","type":"inject","z":"184dc884.7aba5f","name":"Add new item to array","topic":"","payload":"blah_","payloadType":"str","repeat":"","crontab":"","once":false,"onceDelay":0.1,"x":190,"y":1220,"wires":[["26162964.640a16"]]}]

```

And this is for the single `wipe` part of the `function` node code:

```auto
        // Delete this item
        j = i + 1;
        node.warn("Removing item " + j + " which is " + queue_array[i]);
        queue_array.splice(i,1);
        flow.set('queue', queue_array);
        return;

```

All seems to work as I want.

(Just copy/paste this in the code at the `delete this item` part is. Which as posted is basically empty.)

Could someone give it a _sanity check_?  
Please.

---

<div class="post-metadata">

**Author:** ![knolleary](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/knolleary/32/3_2.png) [@knolleary](https://discourse.nodered.org/u/knolleary)\
**Post date:** [20 January 2020 11:20 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/29 "2020-01-20T11:20:58Z")

</div>

> [@Trying\_to\_learn](#):
>
> Ok, I'm stuck.
> 
> `node.warn("Next entry " + i+1);`
> 
> Doesn't work.
> 
> I get `11` if i = `1` .

The problem here is JavaScript uses the `+` symbol for both joining strings and adding numbers.

Because your statement has a string in it (the `"Next entry "` part), it will assume it should treat everything as a string, so the `1` ends up being `11` - just as `8` would end up as `81`.

The trick is to give the JavaScript interpreter a hint as to what order it should do the operations. I see you've used spaces in your statement, but you need to use brackets:

```auto
node.warn("Next entry " + (i+1) );

```

With those brackets, it will first do the `i+1`- where both sides are numbers, so it does numeric addition. It then does `"Next entry " + <result of (i+1)>` where there is a String, so it does a string join.

I hope that clarifies it.

---

<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:** [20 January 2020 11:24 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/30 "2020-01-20T11:24:09Z")

</div>

Yes, thanks Nic.

I was suspicious of doing that. It is I have just spent the last . . . . (long time) getting this working and am starting to lose self belief.

I'll go in and modify the code now.

That kind of lies with the old _BASIC_ syntax. But . . . . . I am good at messing things up and just hadn't got around to trying that.

Self doubt isn't a good thing.

---

<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:** [20 January 2020 11:36 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/31 "2020-01-20T11:36:42Z")

</div>

I've posted the working flow here if you want to look at it and have a look at what I did.

[Working flow](https://discourse.nodered.org/t/how-to-create-an-array-list-individual-entries-and-delete-slected-items/20621)

---

<div class="post-metadata">

**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [20 January 2020 12:28 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/32 "2020-01-20T12:28:14Z")

</div>

Since we should all now be using newer versions of Node.js, we can also make use of ES6 features. So a nice way to output a string with an embedded simple calculation is:

```auto
node.warn( `Next entry ${i+1}` );

```

Note the backticks

---

<div class="post-metadata">

**Author:** ![cymplecy](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/cymplecy/32/2773_2.png) [@cymplecy](https://discourse.nodered.org/u/cymplecy)\
**Post date:** [20 January 2020 13:28 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/33 "2020-01-20T13:28:50Z")

</div>

> [@TotallyInformation](#):
>
> So a nice way to output a string with an embedded simple calculation is:

I think us JS muggles should stick with the simplest way of doing something 🙂

You wizards can do things the fancy ways 🙂  
#KISS

---

<div class="post-metadata">

**Author:** ![TotallyInformation](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/totallyinformation/32/31_2.png) [@TotallyInformation](https://discourse.nodered.org/u/TotallyInformation)\
**Post date:** [20 January 2020 18:00 UTC](https://discourse.nodered.org/t/message-queue-node-that-can-be-indexed/20555/34 "2020-01-20T18:00:13Z")

</div>

Haha, I would argue that, in this case, the fancy way may well **be** the easiest 😀

Anyway, it is through learning new ways that we keep ourselves youthful - or "childish" as our better halves would doubtless characterise things. 🤣

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