In reply to Justin Tadlock.

The problem is not with "how to do X", the problem with all JS frameworks is with "WTF X is not working" moments. In wordpress media you have backbone over underscore over jquery. This is three times removed from what the browser actually does and what the browser debuging tools provide. The need to learn totally different concepts to understand how backbone and underscore actually work make the media library impossible to hack. As a contrast, the customizer code is ugly, but because it do not have the additional abstraction layers it is at least possible to follow and debug it.