You don’t need anything more than html/css/js knowledge. You do need to be able to follow instructions 
Try here and go through the thing it should get you a nice hello world app going: https://dev.twitch.tv/docs/extensions/
You don’t need anything more than html/css/js knowledge. You do need to be able to follow instructions Try here and go through the thing it should get you a nice hello world app going: https://dev.twitch.tv/docs/extensions/