!function (win) {
    var isIE = !!window.ActiveXObject;
    var isIE6 = isIE && !window.XMLHttpRequest;
    var isIE8 = isIE && !!document.documentMode;
    var isIE7 = isIE && !isIE6 && !isIE8;

    var v, initial_scale, timeCode, dom = win.document, domEle = dom.documentElement, viewport = dom.querySelector('meta[name="viewport"]'), flexible = dom.querySelector('meta[name="flexible"]');
    if (viewport) {
        var o = viewport.getAttribute("content").match(/initial\-scale=(["']?)([\d\.]+)\1?/);
        if (o) {
            initial_scale = parseFloat(o[2]);
            v = parseInt(1 / initial_scale);
        }
    } else if (flexible) {
        var o = flexible.getAttribute("content").match(/initial\-dpr=(["']?)([\d\.]+)\1?/);
        if (o) {
            v = parseFloat(o[2]);
            initial_scale = parseFloat((1 / v).toFixed(2))
        }
    }
    if (!v && !initial_scale) {
        var n = (win.navigator.appVersion.match(/android/gi), win.navigator.appVersion.match(/iphone/gi));
        v = win.devicePixelRatio;
        v = n ? v >= 3 ? 3 : v >= 2 ? 2 : 1 : 1, initial_scale = 1 / v
    }
    //没有viewport标签的情况下
    if (domEle.setAttribute("data-dpr", v), !viewport) {
        if (viewport = dom.createElement("meta"), viewport.setAttribute("name", "viewport"), viewport.setAttribute("content", "initial-scale=" + initial_scale + ", maximum-scale=" + initial_scale + ", minimum-scale=" + initial_scale + ", user-scalable=no"), domEle.firstElementChild) {
            domEle.firstElementChild.appendChild(viewport)
        } else {
            var m = dom.createElement("div");
            m.appendChild(viewport), dom.write(m.innerHTML)
        }
    }
    function resize() {
        var domWidth = 0;
        if (isIE8 || isIE7) {
            domWidth = domEle.getBoundingClientRect().right;
        }else{
            domWidth = domEle.getBoundingClientRect().width;
        }
        if (domWidth / v > 540) {
            domWidth = 540 * v;
        }
        win.rem = domWidth / 16;
        domEle.style.fontSize = win.rem + "px";
    }

    win.dpr = v;


    if (isIE8 || isIE7) {
        win.attachEvent("onresize", function () {
            clearTimeout(timeCode), timeCode = setTimeout(resize, 300)
        });
        win.attachEvent("onpageshow", function (b) {
            b.persisted && (clearTimeout(timeCode), timeCode = setTimeout(resize, 300))
        });
    } else {
        win.addEventListener("resize", function () {
            clearTimeout(timeCode), timeCode = setTimeout(resize, 300)
        }, false);
        win.addEventListener("pageshow", function (b) {
            b.persisted && (clearTimeout(timeCode), timeCode = setTimeout(resize, 300))
        }, false);
    }

    resize();
}(window);