动端(手机端)页面自适应解决方案—rem布局
假设设计妹妹给我们的设计稿尺寸为750 * 1340。结合网易、淘宝移动端首页html元素上的动态font-size属性、设计稿尺寸、前端与设计之间协作流程一般分为下面两种：
一、网易做法：
引入：页面开头处引入下面这段代码，用于动态计算font-size
(function(doc, win) {var docEl = doc.documentElement,isIOS = navigator.userAgent.match(/\(i[^;]+;( U;)? CPU.+Mac OS X/),dpr = isIOS ? Math.min(win.devicePixelRatio, 3) : 1,dpr = window.top === window.self ? dpr : 1, //被iframe引用时，禁止缩放dpr = 1,scale = 1 / dpr,resizeEvt = 'orientationchange' in window ? 'orientationchange' : 'resize';docEl.dataset.dpr = dpr;var metaEl = doc.createElement('meta');metaEl.name = 'viewport';metaEl.content = 'initial-scale=' + scale + ',maximum-scale=' + scale + ', minimum-scale=' + scale;docEl.firstElementChild.appendChild(metaEl);var recalc = function() {var width = docEl.clientWidth;if (width / dpr > 750) {width = 750 * dpr;}// 乘以100，px : rem = 100 : 1docEl.style.fontSize = 100 * (width / 750) + 'px';};recalc()if (!doc.addEventListener) return;win.addEventListener(resizeEvt, recalc, false);})(document, window);
使用：
未引入前：
body {width: 750px;height: 640px;}
引入后：除以100并将px换成rem
body {width: 7.5rem;height: 6.4rem;}
换算的依据：
// 乘以100，px : rem = 100 : 1var recalc = function() {var width = docEl.clientWidth;if (width / dpr > 750) {width = 750 * dpr;}// 乘以100，px : rem = 100 : 1docEl.style.fontSize = 100 * (width / 750) + 'px';};
二、淘宝做法（推荐做法，尤其是app内嵌页面）：
引入：页面开头处引入下面这段代码，用于动态计算font-size，或者单独放入一个文件，引入文件也可以
;(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) {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;// 适配平板if (width / dpr > 540) {width = 540 * dpr;}var rem = width / 10;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'] = {}));
使用：
未引入前：
body {width: 750px;height: 640px;}
引入后：
@font-size-base: 75;body {width: 750rem/@font-size-base;height: 640rem/@font-size-base;}
换算依据：
function refreshRem() {var width = docEl.getBoundingClientRect().width;// 适配平板if (width / dpr > 540) {width = 540 * dpr;}var rem = width / 10;docEl.style.fontSize = rem + 'px';flexible.rem = win.rem = rem;}
这边是用的less，如果您没有用less，就需要手动计算，当然也可以转化为px : rem = 100 : 1。
如果想转化为px : rem = 100 : 1，可以修改上面的refreshRem函数：
function refreshRem() {var width = docEl.getBoundingClientRect().width// 适配平板if (width / dpr > 750) {width = 750 * dpr}var rem = 100 * (width / 750)docEl.style.fontSize = rem + 'px'flexible.rem = win.rem = rem;}
使用：
未引入前：
body {width: 750px;height: 640px;}
引入后：除以100并将px换成rem
body {width: 7.5rem;height: 6.4rem;}
换算依据就是上面修改的代码：
function refreshRem() {var width = docEl.getBoundingClientRect().width// 适配平板if (width / dpr > 750) {width = 750 * dpr}var rem = 100 * (width / 750)docEl.style.fontSize = rem + 'px'flexible.rem = win.rem = rem;}
