rem.js

(function(doc, win) {

var docEl = doc.documentElement,

resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',

recalc = function() { 

var clientWidth = docEl.clientWidth;

if (!clientWidth) return;

docEl.style.fontSize = 50 * (clientWidth / 320) + 'px';

 

 

};

if (!doc.addEventListener) return;

win.addEventListener(resizeEvt, recalc, false);

doc.addEventListener('DOMContentLoaded', recalc, false);

})(document, window);