移动端动态font-size

/**
 * Created by shimin on 2017/8/18.
 */
//计算dpr
!function(win, lib) {
    var timer,
        doc     = win.document,
        docElem = doc.documentElement,

        vpMeta   = doc.querySelector('meta[name="viewport"]'),
        flexMeta = doc.querySelector('meta[name="flexible"]'),

        dpr   = 0,
        scale = 0,

        flexible = lib.flexible || (lib.flexible = {});

    // 设置了 viewport meta
    if (vpMeta) {

        console.warn("将根据已有的meta标签来设置缩放比例");
        var initial = vpMeta.getAttribute("content").match(/initial\-scale=([\d\.]+)/);

        if (initial) {
            scale = parseFloat(initial[1]); // 已设置的 initialScale
            dpr = parseInt(1 / scale);      // 设备像素比 devicePixelRatio
        }

    }
    // 设置了 flexible Meta
    else if (flexMeta) {
        var flexMetaContent = flexMeta.getAttribute("content");
        if (flexMetaContent) {

            var initial = flexMetaContent.match(/initial\-dpr=([\d\.]+)/),
                maximum = flexMetaContent.match(/maximum\-dpr=([\d\.]+)/);

            if (initial) {
                dpr = parseFloat(initial[1]);
                scale = parseFloat((1 / dpr).toFixed(2));
            }

            if (maximum) {
                dpr = parseFloat(maximum[1]);
                scale = parseFloat((1 / dpr).toFixed(2));
            }
        }
    }

    // viewport 或 flexible
    // meta 均未设置
    if (!dpr && !scale) {
        // QST
        // 这里的 第一句有什么用 ?
        // 和 Android 有毛关系 ?
        var u = (win.navigator.appVersion.match(/android/gi), win.navigator.appVersion.match(/iphone/gi)),
            _dpr = win.devicePixelRatio;

        // 所以这里似乎是将所有 Android 设备都设置为 1 了
        dpr = u ? ( (_dpr >= 3 && (!dpr || dpr >= 3))
                ? 3
                : (_dpr >= 2 && (!dpr || dpr >= 2))
                    ? 2
                    : 1
        )
            : 1;

        scale = 1 / dpr;
    }

    docElem.setAttribute("data-dpr", dpr);

    // 插入 viewport meta
    if (!vpMeta) {
        vpMeta = doc.createElement("meta");

        vpMeta.setAttribute("name", "viewport");
        vpMeta.setAttribute("content",
            "initial-scale=" + scale + ", maximum-scale=" + scale + ", minimum-scale=" + scale + ", user-scalable=no");

        if (docElem.firstElementChild) {
            docElem.firstElementChild.appendChild(vpMeta)
        } else {
            var div = doc.createElement("div");
            div.appendChild(vpMeta);
            doc.write(div.innerHTML);
        }
    }

    function setFontSize() {
        var winWidth = docElem.getBoundingClientRect().width;

        if (winWidth / dpr > 540) {            (winWidth = 540 * dpr);        }        // 根节点 fontSize 根据宽度决定        var baseSize = winWidth / 10;        docElem.style.fontSize = baseSize + "px";        flexible.rem = win.rem = baseSize;    }    // 调整窗口时重置    win.addEventListener("resize", function() {        clearTimeout(timer);        timer = setTimeout(setFontSize, 300);    }, false);    // 这一段是我自己加的    // orientationchange 时也需要重算下吧    win.addEventListener("orientationchange", function() {        clearTimeout(timer);        timer = setTimeout(setFontSize, 300);    }, false);    // pageshow    // keyword: 倒退 缓存相关    win.addEventListener("pageshow", function(e) {        if (e.persisted) {            clearTimeout(timer);            timer = setTimeout(setFontSize, 300);        }    }, false);    // 设置基准字体    if ("complete" === doc.readyState) {        doc.body.style.fontSize = 12 * dpr + "px";    } else {        doc.addEventListener("DOMContentLoaded", function() {            doc.body.style.fontSize = 12 * dpr + "px";        }, false);    }    setFontSize();    flexible.dpr = win.dpr = dpr;    flexible.refreshRem = setFontSize;    flexible.rem2px = function(d) {        var c = parseFloat(d) * this.rem;        if ("string" == typeof d && d.match(/rem$/)) {            c += "px";        }        return c;    };    flexible.px2rem = function(d) {        var c = parseFloat(d) / this.rem;        if ("string" == typeof d && d.match(/px$/)) {            c += "rem";        }        return c;    }}(window, window.lib || (window.lib = {}));//计算viewport!(function(doc, win) {    var docEle = doc.documentElement,        evt = "onorientationchange" in window ? "orientationchange" : "resize",        fn = function() {            var width = docEle.clientWidth;            width && (docEle.style.fontSize = 20 * (width / 320) + "px");        };    win.addEventListener(evt, fn, false);    doc.addEventListener("DOMContentLoaded", fn, false);}(document, window));//媒体查询设置rem@media screen and (min-width: 320px) {    html {font-size: 14px;}}@media screen and (min-width: 360px) {    html {font-size: 16px;}}@media screen and (min-width: 400px) {    html {font-size: 18px;}}@media screen and (min-width: 440px) {    html {font-size: 20px;}}@media screen and (min-width: 480px) {    html {font-size: 22px;}}@media screen and (min-width: 640px) {    html {font-size: 28px;}}