Caching. That you control in code - not controlled by server headers which never worked reliably back to the earliest days. Already addressed in browsers in win

Caching. That you control in code - not controlled by server headers which never worked reliably back to the earliest days. Already addressed in browsers in window.caches, serviceworker. It's not so much you need JQuery version x cached from another origin, but once its loaded from your site, it never needs to be sent again. Heck you cache everything, or everything except index.html if you want to.