rem适配代码段

(function () {
                var resizeEvent = 'orientationchange'in window ? 'orientationchange' :'resize';
                var rescale = function(){
                    document.documentElement.style.fontSize = document.documentElement.clientWidth / 320 *20 + 'px';
                }
                window.addEventListener(resizeEvent,rescale,false);
                document.addEventListener('DOMContentLoaded',rescale,false);
            })();