移动端应用rem定义相对长度单位

    (function (doc, win) {
        var fs = document.body.clientWidth / 750 * 28;
        fs = fs > 24 ? 24 : fs;
        fs = fs < 12 ? 12 : fs;
        document.documentElement.style.fontSize = fs + "px";

        var docEl = doc.documentElement,
            resizeEvt = ‘orientationchange‘ in window ? ‘orientationchange‘ : ‘resize‘,
            recalc = function () {
                var clientWidth = docEl.clientWidth;
                if (!clientWidth) return;
                if (clientWidth >= 750) {
                    docEl.style.fontSize = ‘100px‘;
                } else {
                    docEl.style.fontSize = 100 * (clientWidth / 750) + ‘px‘;
                }
            };

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