rem单位适配

(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);    recalc();})(document, window)