Proxying website use backend

Hello.
I have an iOS app where needs a proxying website through private server(HTTP / HTTPS proxy), but its idea each time has some trouble, when I am trying to solve their on the client-side, how I can solve this problem use the back end.

IMPORTANT: need proxying website which has various type of JavaScript. Appearing idea use anonymizer, I am trying various websites like 2ip and another anonymizer, it’s work good BUT when I use anonymizer for a web site like, youtube which have JS I can’t saw video content, If the site has PHP it’s not a problem looking a video content through a proxy.

Question: How I can solve this problem use back end(Technology doesn`t matter) if I want proxying websites with video content through a proxy, and these sites have JS?