计算rem

(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 = 100 * (clientWidth / 375) + 'px';

};
if(!doc.addEventListener) return;
win.addEventListener(resizeEvt, recalc, false);
doc.addEventListener('DOMContentLoaded', recalc, false);
})(document, window);