This is the best answer by far. I got a job because of my Javascript skills and was able to translate a OLD site into a mobile ready site with ONLY javascript in 2 days (Trust me adding or changing existing css on this platform that was custom for them was almost impossible). It would generate a 2nd body tag (body_mobile) and if on mobile or during scale would hide the main one and show the mobile version and pull links and other content based on enclosed HTML elements.