1.下载lib-flexible

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

2.在项目中引入lib-flexible 平常状况在(main.js中引入lib-flexible)

import 'lib-flexible/flexible'

3.设置meta标签(视状况而定)

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

4.装置px2rem-loader

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

5.在webpack中设置px2rem-loader

1，在项目build文件中找到util.js，将px2rem-loader增加到cssLoaders中，
2，px2rem-loader 下的 remUnit 依据设想稿而定
详细以下：

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 // 因为设想稿是750
    }
  }

  function generateLoaders (loader, loaderOptions) {
    var loaders = [cssLoader,px2remLoader]//增加到loader内里
    省略.....
  }
}

6.项目中运用

假定设想稿width和font-size分别是200px，50px
详细代码：(根据设想稿写即可)

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

7.零丁运用flexible可直接增加一个rem.js文件，详细以下：

1，合营less，sass和stylus来做px转换rem
2，详细可参看css编译

/*
** 挪动端自适应计划  FROM 手淘
*/
export const setViewport = (()=>{//此处是零丁运用
    const win = window
    const lib = window.lib || (window.lib = {})
//;(function(win, lib) {//此处是直接运用
    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('将依据已有的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，关于2和3的屏，用2倍的计划，其他的用1倍计划
            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，依旧运用1倍的计划
            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 = {}));