How to have one static folder per app ?

Let’s say I have three app: app1, app2, app3, and would like to get my static files independently

What should be the syntax in ?

> STATIC_URL = '/static/'
>     os.path.join(BASE_DIR, "static"),
>     '/app1/static/',
>     '/app2/static/',
>     '/app3/static/',
> )

Then in each templates/web files, does it mean I just need

<script src="{% static 'start.js' %}"></script>

or do I need to specify more ?

While you can do it that way, Django does define a convention that is slightly different. See the docs at How to manage static files (e.g. images, JavaScript, CSS) | Django documentation | Django