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'] = {}));
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;
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