How to start to develope own functions in ArcGIS Online

[KaiBehncke]

Maybe someone can give me some precise hints.
I work since longtimes in the field of WebMapping and have experiences with
different WebMapping clients (OpenLayers, Mapbender etc.) and different formats and scripting languages
(PHP,JS....)

Now I want to build own functions in ArcGIS Online.
But I don`t know how to start (by the way, we have no ArcGIS or other ESRI products so far)?

I found that link https://developers.arcgis.com/javascript/latest/
but I always stumble about terms like "ArcGIS Maps SDK for JavaScript"...?(we don`t have ArcGIS, I would like to change ArcGIS Online).
Or is the "ArcGIS Maps SDK for JavaScript" exactly what one needs for AGO?

Does anybody know a good basic-tutorial how to create an own function in AGO?
Thank you very much, Kai

[Katie_Clark]

I'm not exactly sure what you mean by writing your own "function" in the context of AGOL, but for custom applications you'll need to host them yourself, not in ArcGIS Online, as AGOL doesn't allow custom code like that for security reasons. You can use ArcGIS Enterprise for this as well. 

If you want to do things like administrative tasks, you can look into using the ArcGIS API for Python. This would be run in ArcGIS Pro or a Notebook, etc. and you can manage your online content programmatically. 

[KaiBehncke]

Dear Katherine,

ok, thank you for answering 🙂

As far as I understand:

a) It is not possible to implement own JS-code in AGO and the Instant Apps or the Map Viewer /Map Viewer Classic, due to security reasons. So it is not possible to write own functions in that clients, rights?

b) It is not possible to download AGO or the Instant Apps to customise them on an own server.(e.g. on a linux server).

c) It is possible to use the ArcGIS Map Api
<script src="https://js.arcgis.com/4.27/"></script>

.....and create own code based on html/css/JS..... But then it`s not possible to you all the nice AGO-functions (creating maps by clicking). Then everything is "just codebased", right?

Is that right, what I have written?