1.下载lib-flexible

npm i lib-flexible --save
或
yarn add lib-flexible

2.在项目中引入lib-flexible 一般情况在(main.js中引入lib-flexible)

import 'lib-flexible/flexible'

3.设置meta标签(视情况而定)

<meta name="viewport" content="width=device-width, initial-scale=1.0">

4.安装px2rem-loader

npm install px2rem-loader   --save
或
yarn add px2rem-loader

5.在webpack中配置px2rem-loader

1，在项目build文件中找到util.js，将px2rem-loader添加到cssLoaders中，
2，px2rem-loader 下的 remUnit 根据设计稿而定
具体如下：

exports.cssLoaders = function (options) {options = options || {}const cssLoader = {loader: 'css-loader',options: {minimize: process.env.NODE_ENV === 'production',sourceMap: options.sourceMap}}//rem编译（新加px2）const px2remLoader = {loader: 'px2rem-loader',options: {remUnit: 75 // 由于设计稿是750}}function generateLoaders (loader, loaderOptions) {var loaders = [cssLoader,px2remLoader]//添加到loader里面省略.....}
}

6.项目中使用

假设设计稿width和font-size分别是200px，50px
具体代码：(按照设计稿写即可)

.demo{width: 200px;font-size: 50px;
}

7.单独使用flexible可直接添加一个rem.js文件，具体如下：

1，配合less，sass和stylus来做px转换rem
2，具体可参看css编译

/*
** 移动端自适应方案  FROM 手淘
*/
export const setViewport = (()=>{//此处是单独使用const win = windowconst lib = window.lib || (window.lib = {})
//;(function(win, lib) {//此处是直接使用let doc = win.document;let docEl = doc.documentElement;let metaEl = doc.querySelector('meta[name="viewport"]');let flexibleEl = doc.querySelector('meta[name="flexible"]');let dpr = 0;let scale = 0;let tid;let 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');let match = metaEl.getAttribute('content').match(/initial\-scale=([\d\.]+)/);if (match) {scale = parseFloat(match[1]);dpr = parseInt(1 / scale);}} else if (flexibleEl) {let content = flexibleEl.getAttribute('content');if (content) {let initialDpr = content.match(/initial\-dpr=([\d\.]+)/);let 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) {//let isAndroid = win.navigator.appVersion.match(/android/gi);let isIPhone = win.navigator.appVersion.match(/iphone/gi);let 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 {let wrap = doc.createElement('div');wrap.appendChild(metaEl);doc.write(wrap.innerHTML);}}function refreshRem(){let width = docEl.getBoundingClientRect().width;if (width / dpr > 540) {width = 540 * dpr;}let 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() {doc.body.style.fontSize = 12 * dpr + 'px';}, false);}refreshRem();flexible.dpr = win.dpr = dpr;flexible.refreshRem = refreshRem;flexible.rem2px = function(d) {let val = parseFloat(d) * this.rem;if (typeof d === 'string' && d.match(/rem$/)) {val += 'px';}return val;};flexible.px2rem = function(d) {let val = parseFloat(d) / this.rem;if (typeof d === 'string' && d.match(/px$/)) {val += 'rem';}return val;};});
//})(window, window.lib || (window.lib = {}));