# How to add to array elements?

**URL:** <https://discourse.nodered.org/t/how-to-add-to-array-elements/34981>\
**Category:** General\
**Created:** [28 October 2020 21:11 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981 "2020-10-28T21:11:26Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![Zerg](https://avatars.discourse-cdn.com/v4/letter/z/6de8d8/32.png) [@Zerg](https://discourse.nodered.org/u/Zerg)\
**Post date:** [28 October 2020 21:11 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981/1 "2020-10-28T21:11:26Z")

</div>

Could you help me to add an element/elements to the array and then display array in the debug window.  
I do something wrong!

```auto
var array = flow.get('array') || "";

flow.set("array", flow.get("array").push(msg.payload));
return [msg];

```

my flow

```auto
[{"id":"8e05673f.25a118","type":"tab","label":"Delay","disabled":false,"info":""},{"id":"e9887f38.771fb","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"100","payloadType":"num","x":170,"y":200,"wires":[["8f92e447.ec7758"]]},{"id":"8f92e447.ec7758","type":"function","z":"8e05673f.25a118","name":"","func":"var array = flow.get('array') || \"\";\n\nflow.set(\"array\", flow.get(\"array\").push(msg.payload));\nreturn [msg];","outputs":1,"noerr":0,"initialize":"","finalize":"","x":400,"y":240,"wires":[["48b4aadb.221d54","f70ea5c3.3a8408"]]},{"id":"f70ea5c3.3a8408","type":"ui_slider","z":"8e05673f.25a118","name":"Brightness","label":"Яркость","tooltip":"","group":"bf8577b0.734c08","order":2,"width":0,"height":0,"passthru":true,"outs":"end","topic":"brightness","min":"1","max":"254","step":1,"x":690,"y":240,"wires":[[]]},{"id":"48b4aadb.221d54","type":"debug","z":"8e05673f.25a118","name":"2","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":410,"y":300,"wires":[]},{"id":"fb80fc91.c062f","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"50","payloadType":"num","x":170,"y":240,"wires":[["8f92e447.ec7758"]]},{"id":"a10f32f8.65f5d","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"0","payloadType":"num","x":170,"y":280,"wires":[["8f92e447.ec7758"]]},{"id":"db752fb9.2d235","type":"function","z":"8e05673f.25a118","name":"array","func":"var array = [];\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":390,"y":160,"wires":[[]]},{"id":"bf8577b0.734c08","type":"ui_group","name":"test","tab":"96dac147.c7906","order":1,"disp":true,"width":"6","collapse":false},{"id":"96dac147.c7906","type":"ui_tab","name":"Array","icon":"dashboard","order":6,"disabled":false,"hidden":false}]

```

---

<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:** [28 October 2020 21:15 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981/2 "2020-10-28T21:15:13Z")

</div>

Hi @zerg,

```auto
var array = flow.get('array') || "";

```

This line will mean, if `array` doesn't exist in context, you are returning a blank string - `""`, not an array.

```auto
flow.set("array", flow.get("array").push(msg.payload));

```

This line we store the result of calling `flow.get("array").push(msg.payload)` into context.  
However, the `Array.push` function returns the length of the array - not the array itself, so that is what this line will be storing.

The correct version of your function is:

```auto
var array = flow.get('array') || [];
array.push(msg.payload);
flow.set("array", array);
return msg;

```

---

<div class="post-metadata">

**Author:** ![Zerg](https://avatars.discourse-cdn.com/v4/letter/z/6de8d8/32.png) [@Zerg](https://discourse.nodered.org/u/Zerg)\
**Post date:** [28 October 2020 22:16 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981/3 "2020-10-28T22:16:04Z")

</div>

Thank you for detailed explanation!  
One more question about array, how to add elements to the array constantly? Because, current solution every time remove all elements from the array and after added a new element?  
Question is: How to save "old" elements in array and every time add new elements?

fixed flow

```auto
[{"id":"8e05673f.25a118","type":"tab","label":"Delay","disabled":false,"info":""},{"id":"e9887f38.771fb","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"100","payloadType":"num","x":170,"y":200,"wires":[["8f92e447.ec7758"]]},{"id":"8f92e447.ec7758","type":"function","z":"8e05673f.25a118","name":"","func":"var array = flow.get('array') || [];\narray.push(msg.payload);\nflow.set(\"array\", array);\nreturn msg;","outputs":1,"noerr":0,"initialize":"","finalize":"","x":400,"y":240,"wires":[["48b4aadb.221d54","f70ea5c3.3a8408"]]},{"id":"f70ea5c3.3a8408","type":"ui_slider","z":"8e05673f.25a118","name":"Brightness","label":"Яркость","tooltip":"","group":"bf8577b0.734c08","order":2,"width":0,"height":0,"passthru":true,"outs":"end","topic":"brightness","min":"1","max":"254","step":1,"x":690,"y":240,"wires":[[]]},{"id":"48b4aadb.221d54","type":"debug","z":"8e05673f.25a118","name":"2","active":true,"tosidebar":true,"console":false,"tostatus":false,"complete":"payload","targetType":"msg","statusVal":"","statusType":"auto","x":410,"y":300,"wires":[]},{"id":"fb80fc91.c062f","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"50","payloadType":"num","x":170,"y":240,"wires":[["8f92e447.ec7758"]]},{"id":"a10f32f8.65f5d","type":"inject","z":"8e05673f.25a118","name":"","props":[{"p":"payload"},{"p":"topic","vt":"str"}],"repeat":"","crontab":"","once":false,"onceDelay":0.1,"topic":"","payload":"0","payloadType":"num","x":170,"y":280,"wires":[["8f92e447.ec7758"]]},{"id":"bf8577b0.734c08","type":"ui_group","name":"test","tab":"96dac147.c7906","order":1,"disp":true,"width":"6","collapse":false},{"id":"96dac147.c7906","type":"ui_tab","name":"Array","icon":"dashboard","order":6,"disabled":false,"hidden":false}]

```

---

<div class="post-metadata">

**Author:** ![Colin](https://sea2.discourse-cdn.com/flex026/user_avatar/discourse.nodered.org/colin/32/17040_2.png) [@Colin](https://discourse.nodered.org/u/Colin)\
**Post date:** [29 October 2020 10:27 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981/4 "2020-10-29T10:27:24Z")

</div>

> [@Zerg](#):
>
> current solution every time remove all elements from the array and after added a new element?

I don't understand what you mean by that. Do you mean that the array is cleared if you do a full Deploy or restart node red? If not that then what is it that clears the array?  
If it _is_ the deploy/restart problem you are worried about then you need to use persistent context so the values are retained over a restart. [Working with context : Node-RED](https://nodered.org/docs/user-guide/context)

---

<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:** [28 December 2020 10:27 UTC](https://discourse.nodered.org/t/how-to-add-to-array-elements/34981/5 "2020-12-28T10:27:29Z")

</div>

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