移动端rem设置，自动更改html<font-size>

<script>        
        (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 = 20 * (clientWidth / 320) + ‘px‘;    
        };    
        if (!doc.addEventListener) return;    
        win.addEventListener(resizeEvt, recalc, false);    
        doc.addEventListener(‘DOMContentLoaded‘, recalc, false);    
        })(document, window);    
 </script>