以rem为单位根据移动设备的分辨率动态设置font-size

无需指定font-size的大小

<script>

    // //- 设置根元素fontSize~
    // (function (doc, win) {
    //     var _root = doc.documentElement,
    //         resizeEvent = 'orientationchange' in window ? 'orientationchange' : 'resize',
    //         resizeCallback = function () {
    //             var clientWidth = _root.clientWidth,
    //                 fontSize = 0;
    //             if (!clientWidth) return;
    //             if(clientWidth < 640) {
    //                 fontSize = clientWidth / 10;
    //             } else {
    //                 fontSize = 640 / 10;
    //             }
    //             _root.style.fontSize = fontSize + 'px';
    //         };
    //     if (!doc.addEventListener) return;
    //     win.addEventListener(resizeEvent, resizeCallback, false);
    //     doc.addEventListener('DOMContentLoaded', resizeCallback, false);
    // })(document, window);
    !
            function(a, b) {
                function c() {
                    var b = f.getBoundingClientRect().width;
                    b / i > 1080 && (b = 1080 * i);
                    var c = b / 10;
                    f.style.fontSize = c + "px", k.rem = a.rem = c
                }
                var d, e = a.document,
                        f = e.documentElement,
                        g = e.querySelector('meta[name="viewport"]'),
                        h = e.querySelector('meta[name="flexible"]'),
                        i = 0,
                        j = 0,
                        k = b.flexible || (b.flexible = {});
                if (g) {
                    console.warn("将根据已有的meta标签来设置缩放比例");
                    var l = g.getAttribute("content").match(/initial\-scale=([\d\.]+)/);
                    l && (j = parseFloat(l[1]), i = parseInt(1 / j))
                } else if (h) {
                    var m = h.getAttribute("content");
                    if (m) {
                        var n = m.match(/initial\-dpr=([\d\.]+)/),
                                o = m.match(/maximum\-dpr=([\d\.]+)/);
                        n && (i = parseFloat(n[1]), j = parseFloat((1 / i).toFixed(2))), o && (i = parseFloat(o[1]), j = parseFloat((1 / i).toFixed(2)))
                    }
                }
                if (!i && !j) {
                    var p = a.navigator.userAgent,
                            q = ( !! p.match(/android/gi), !! p.match(/iphone/gi)),
                            r = q && !! p.match(/OS 9_3/),
                            s = a.devicePixelRatio;
                    i = q && !r ? s >= 3 && (!i || i >= 3) ? 3 : s >= 2 && (!i || i >= 2) ? 2 : 1 : 1, j = 1 / i
                }
                if (f.setAttribute("data-dpr", i), !g) if (g = e.createElement("meta"), g.setAttribute("name", "viewport"), g.setAttribute("content", "initial-scale=" + j + ", maximum-scale=" + j + ", minimum-scale=" + j + ", user-scalable=no"), f.firstElementChild) f.firstElementChild.appendChild(g);
                else {
                    var t = e.createElement("div");
                    t.appendChild(g), e.write(t.innerHTML)
                }
                a.addEventListener("resize", function() {
                    clearTimeout(d), d = setTimeout(c, 300)
                }, !1), a.addEventListener("pageshow", function(a) {
                    a.persisted && (clearTimeout(d), d = setTimeout(c, 300))
                }, !1), "complete" === e.readyState ? e.body.style.fontSize = 12 * i + "px" : e.addEventListener("DOMContentLoaded", function() {
                    e.body.style.fontSize = 12 * i + "px"
                }, !1), c(), k.dpr = a.dpr = i, k.refreshRem = c, k.rem2px = function(a) {
                    var b = parseFloat(a) * this.rem;
                    return "string" == typeof a && a.match(/rem$/) && (b += "px"), b
                }, k.px2rem = function(a) {
                    var b = parseFloat(a) / this.rem;
                    return "string" == typeof a && a.match(/px$/) && (b += "rem"), b
                }
            }(window, window.lib || (window.lib = {}));
</script>