Custom Javascript in Control Panel (getting started with Extensions)

I’m jumping into creating my first control panel extension to create a jquery based WYSIWYG editor. I’ve followed the docs for creating a base extension and the programming doesn’t bother me any, just wondering if someone can help me establish what hook I would need to tie into to get my own custom JS in the cpanel so that I can instantiate an editor on custom selectors / textareas.

I’ve tried to tie into the cp_js_end hook but I need a little direction for how to actually push a script out using this hook, as well as any insight or suggestions for other extension docs or tutorials that may help.

For the record I am well aware of wygwam and other editors that exist by creating custom field types, but I’m aiming to build an extension that solves the problem of WYSIWYG for large sites that have already been built on EE using simple textarea field types (unless there is an easy way to migrate all existing textareas to a new field type, but from my research nothing of the sort exists).

Thanks!