摘要：下載或在項目中引入一般情況在中引入設置標簽視情況而定安裝或在中配置，在項目文件中找到，將添加到中，，下的根據設計稿而定具體如下編譯新加由于設計稿是添加到里面省略項目中使用假設設計稿和分別是，具體代碼

1.下載lib-flexible

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

2.在項目中引入lib-flexible 一般情況在(main.js中引入lib-flexible)

import "lib-flexible/flexible"

3.設置meta標簽(視情況而定)

4.安裝px2rem-loader

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

5.在webpack中配置px2rem-loader

1，在項目build文件中找到util.js，將px2rem-loader添加到cssLoaders中，
2，px2rem-loader 下的 remUnit 根據設計稿而定
具體如下：

exports.cssLoaders = function (options) {
  options = options || {}

  const cssLoader = {
    loader: "css-loader",
    options: {
      minimize: process.env.NODE_ENV === "production",
      sourceMap: options.sourceMap
    }
  }
  //rem編譯（新加px2）
  const px2remLoader = {
    loader: "px2rem-loader",
    options: {
      remUnit: 75 // 由于設計稿是750
    }
  }

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

6.項目中使用

假設設計稿width和font-size分別是200px，50px
具體代碼：(按照設計稿寫即可)

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

7.多帶帶使用flexible可直接添加一個rem.js文件，具體如下：

1，配合less，sass和stylus來做px轉換rem
2，具體可參看css編譯

/*
** 移動端自適應方案  FROM 手淘
*/
export const setViewport = (()=>{//此處是多帶帶使用
    const win = window
    const lib = window.lib || (window.lib = {})
//;(function(win, lib) {//此處是直接使用
    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("將根據已有的meta標簽來設置縮放比例");
        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，對于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 {
            // 其他設備下，仍舊使用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 = {}));