rem适配问题

(function (doc, win) {
    var docEl = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize',//判断设备的方向变化（横竖屏）事件
        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);

body{font-size:20px}
说明：iphone4/5/5s(320px)下，1rem = 20px