Supporting cardinality (i.e. preventing how many items can be selected with JS)

To make this patch work you have to set your entity browser to Selection display plugin: None in General information.
Then in widget setting you have to uncheck Automatically submit selection on your view.

The problem is that using multi-step selection like in the File Browser included solution Drupal keeps detaching and re-attaching the behaviors after each file selection, side-stepping the Onclick function. I didn't see how to make this work with the multi selection. However, the patch does not break behavior for multi step selection, it just doesn't provide the cardinality support.

I think it would be better to just move away from the multi step selection because it's not what users expect, I also think it's confusing you can select one file multiple times when clicking. The industry standard is to unselect when clicking a selected file and in UX following these standards is super important.

Please note the users I credited in the commit message since I just ported over their code.

I see adding things in the commit message field didn't work, how to I attribute the patch? The original authors are RajabNatshah, phenaproxima, balsama

Fixing backbone error

no prob! unfortunately it is not, the flexibility of the whole system is great but it's also making it hard to apply style and behavior in a generic way.
We don't need much in terms of structure to hook onto though, it's mostly the grid-item class we're targeting here that is not available elswhere. Then again grid rows can take on many different HTML structures, it's practically impossible to support all. I imagine there might be one person trying to use a complex SOLR view for entity browsing and another poor soul who is integrating some data view that comes with it's own features. etc.

The most generic solution I can think of is targeting all image elements within the view.

Understood, yeah it's quite a lot to test and I can imagine you'll find areas that can use refinement. I'd personally like to copy over the use of the checkmark icon in the dropzone tab to the library tab.
Also I'm doing a quick re-upload of the patch here because the previous one contains a console.log message.

For anyone interested in including the patch is his website or installation profile, at the bottom of this blog post there's a video showing how single-file fields, multifile fields, and unlimited fields are handled: https://www.sooperthemes.com/drupal-blog/8-days-drupal-8-media-managemen...