rem自动计算

 写法一：

//rem自动计算
(function (designWidth, maxWidth, viewWidth) {
    var doc = document,
        win = window,
        docEl = doc.documentElement,
        remStyle = document.createElement("style"),
        tid;

    function refreshRem() {
        var width = docEl.getBoundingClientRect().width;
        maxWidth = maxWidth || 540;
        width > maxWidth && (width = maxWidth);
        var rem = width * 100 / designWidth;
        if (viewWidth == null || viewWidth < maxWidth) {
            remStyle.innerHTML = 'html{font-size:' + rem + 'px;}';
        } else {
            remStyle.innerHTML = 'html{font-size:' + rem + 'px; max-' + viewWidth + 'px; margin: auto}';
        }
    }

    if (docEl.firstElementChild) {
        docEl.firstElementChild.appendChild(remStyle);
    } else {
        var wrap = doc.createElement("div");
        wrap.appendChild(remStyle);
        doc.write(wrap.innerHTML);
        wrap = null;
    }
    refreshRem();

    win.addEventListener("resize", function () {
        clearTimeout(tid);
        tid = setTimeout(refreshRem, 300);
    }, false);

    win.addEventListener("pageshow", function (e) {
        if (e.persisted) {
            clearTimeout(tid);
            tid = setTimeout(refreshRem, 300);
        }
    }, false);

    if (doc.readyState === "complete") {
        doc.body.style.fontSize = "16px";
    } else {
        doc.addEventListener("DOMContentLoaded", function (e) {
            doc.body.style.fontSize = "16px";

        }, false);
    }
})(750, 750);

写法二：

//修改页面title
var pageTitle=document.getElementsByTagName("title")[0].innerHTML;
if(location.href.indexOf("index.html")>-1 || location.href.indexOf("html")==-1){
    document.getElementsByTagName("title")[0].innerHTML="一汽-大众商城-一汽-大众官方电商平台-只为简单汽车生活";
}
//微信JSSDK
document.write('<script type="text/javascript" src="https://res.wx.qq.com/open/js/jweixin-1.3.2.js"></script>');
//rem自动计算
(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 / 750) + 'px';
        };

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

写法三：

//rem自动计算
(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 / 750) + 'px';
        };

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