关于移动端rem单位对应响应屏幕

参考京东2018年的rem单位设置(比例已经过整改)：

;(function(win) {
    var doc = win.document;
    var docEl = doc.documentElement;
    var ADD_STYLE = document.createElement("style");
    ADD_STYLE.id = "public_style";
    doc.querySelector("head").appendChild(ADD_STYLE);
    function rem(){
        var e,b=doc.querySelector("#public_style"),
        c=document.documentElement.clientWidth||document.body.clientWidth,d=1;
        d=c/750,e=100*d,b.innerHTML="html{font-size:"+e+"px;}",a=d; window._z = d;
    }
    var a=0;rem(),window.addEventListener("resize",rem);
})(window);

 

 

 

参考淘宝2018年的rem单位设置(比例已经过整改)：

!function(e, t) {
    var n = t.documentElement,
    d = e.devicePixelRatio || 1;
    function i(){
        var e = n.clientWidth / 7.50;
          n.style.fontSize = e + "px"
    } 
    if(function e(){ 
        t.body ? t.body.style.fontSize = "16px" : t.addEventListener("DOMContentLoaded", e) 
    }(),i(), e.addEventListener("resize", i),
    e.addEventListener("pageshow", function(e){ 
        e.persisted && i()
    }),d >= 2){
        var o = t.createElement("body"),
        a = t.createElement("div");
        a.style.border = ".5px solid transparent", o.appendChild(a), n.appendChild(o), 1 === a.offsetHeight && n.classList.add("hairlines"), n.removeChild(o)
    }
}(window, document)

 

 

 

参考腾讯2018年的rem单位设置

    <script type="text/javascript">
        'use strict';

(function (doc, win) {
    var width = 750;
    var height = 1500;
    var docEl = doc.documentElement;
    var rszEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';
    var reCalc = function () {
        var reCalc = function reCalc() {
            var winWidth = docEl.clientWidth;
            var winHeight = docEl.clientHeight;
            if (!winWidth) return;
            var fontSize;
            if (winWidth < winHeight) {
                if (winWidth / winHeight > height / width) {
                    fontSize = 100 * (winHeight / height);
                } else {
                    fontSize = 100 * (winWidth / width);
                }
            } else {
                if (winWidth / winHeight > height / width) {
                    fontSize = 100 * (winWidth / height);
                } else {
                    fontSize = 100 * (winHeight / width);
                }
            }
            docEl.style.fontSize = (fontSize > 110 ? 110 : fontSize) + 'px';
            return reCalc;
        };
        return reCalc();
    }();
    if (!doc.addEventListener) return;
    win.addEventListener(rszEvt, reCalc);
})(document, window);
    </script>

 

 

 

 

参考天猫2015年的rem单位设置(比例已经过整改)：

;(function(win, lib) {
    var doc = win.document;
    var docEl = doc.documentElement;
    var metaEl = doc.querySelector('meta[name="viewport"]');
    var flexibleEl = doc.querySelector('meta[name="flexible"]');
    var dpr = 0;
    var scale = 0;
    var tid;
    var flexible = lib.flexible || (lib.flexible = {});
    
    if (metaEl) {
        console.warn('将根据已有的meta标签来设置缩放比例');
        var match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);
        if (match) {
            scale = parseFloat(match[1]);
            dpr = parseInt(1 / scale);
        }
    } else if (flexibleEl) {
        var content = flexibleEl.getAttribute('content');
        if (content) {
            var initialDpr = content.match(/initial\-dpr=([\d\.]+)/);
            var maximumDpr = content.match(/maximum\-dpr=([\d\.]+)/);
            if (initialDpr) {
                dpr = parseFloat(initialDpr[1]);
                scale = parseFloat((1 / dpr).toFixed(2));    
            }
            if (maximumDpr) {
                dpr = parseFloat(maximumDpr[1]);
                scale = parseFloat((1 / dpr).toFixed(2));    
            }
        }
    }

    if (!dpr && !scale) {
        var isAndroid = win.navigator.appVersion.match(/android/gi);
        var isIPhone = win.navigator.appVersion.match(/iphone/gi);
        var devicePixelRatio = win.devicePixelRatio;
        if (isIPhone) {
            // iOS下，对于2和3的屏，用2倍的方案，其余的用1倍方案
            if (devicePixelRatio >= 3 && (!dpr || dpr >= 3)) {                
                dpr = 3;
            } else if (devicePixelRatio >= 2 && (!dpr || dpr >= 2)){
                dpr = 2;
            } else {
                dpr = 1;
            }
        } else {
            // 其他设备下，仍旧使用1倍的方案
            dpr = 1;
        }
        scale = 1 / dpr;
    }

    docEl.setAttribute('data-dpr', dpr);
    if (!metaEl) {
        metaEl = doc.createElement('meta');
        metaEl.setAttribute('name', 'viewport');
        metaEl.setAttribute('content', 'initial-scale=' + scale + ', maximum-scale=' + scale + ', minimum-scale=' + scale + ', user-scalable=no');
        if (docEl.firstElementChild) {
            docEl.firstElementChild.appendChild(metaEl);
        } else {
            var wrap = doc.createElement('div');
            wrap.appendChild(metaEl);
            doc.write(wrap.innerHTML);
        }
    }

    function refreshRem(){
        var width = docEl.getBoundingClientRect().width;
        if (width / dpr > 540) {
            width = 540 * dpr;
        }
        var rem = width / 7.5;
        docEl.style.fontSize = rem + 'px';
        flexible.rem = win.rem = rem;
    }

    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 = 12 * dpr + 'px';
    } else {
        doc.addEventListener('DOMContentLoaded', function(e) {
            doc.body.style.fontSize = 12 * dpr + 'px';
        }, false);
    }
    

    refreshRem();

    flexible.dpr = win.dpr = dpr;
    flexible.refreshRem = refreshRem;
    flexible.rem2px = function(d) {
        var val = parseFloat(d) * this.rem;
        if (typeof d === 'string' && d.match(/rem$/)) {
            val += 'px';
        }
        return val;
    }
    flexible.px2rem = function(d) {
        var val = parseFloat(d) / this.rem;
        if (typeof d === 'string' && d.match(/px$/)) {
            val += 'rem';
        }
        return val;
    }

})(window, window['lib'] || (window['lib'] = {}));



这是GitHub里面选取淘宝适配代码  原文地址：【https://github.com/amfe/lib-flexible/blob/master/src/flexible.js】

 

 

参考以上设置，几乎都是更改html标签上的fontSize大小来设配内部元素设置的rem值；

数值更改为：用设计图750像素的参考单位下，1rem = 100px;