摘要：小組最近在二次開發一個開源項目，前端主要使用的技術棧試。所以需要對作出如下的改動。原文件變動后至此，我們大部分的優化的內容已經完成，下面是我們打包時間的一個對比。

webpack是當下前端界中最著名的一個模塊加載工具，react和vue也都是用其作為項目的開發工具之一。小組最近在二次開發一個開源項目，前端主要使用的技術棧試react+redux+es6。構建工具則采用的是webpack。起初整個項目的2707 modules打包花費時長大概有112s，經過對一番折騰，使整個打包編譯時間降到40s左右。

下面是整個項目的webpack.config.js文件，可以參考這個文件進行下面的閱讀。

require("babel-register");
require("babel-polyfill");

var webpack = require("webpack");
var webpackPostcssTools = require("webpack-postcss-tools");

var ExtractTextPlugin = require("extract-text-webpack-plugin");
var HtmlWebpackPlugin = require("html-webpack-plugin");
var HtmlWebpackHarddiskPlugin = require("html-webpack-harddisk-plugin");
var UnusedFilesWebpackPlugin = require("unused-files-webpack-plugin").default;
var BannerWebpackPlugin = require("banner-webpack-plugin");
var AddAssetHtmlPlugin = require("add-asset-html-webpack-plugin");
var HappyPack = require("happypack");
var ParallelUglifyPlugin = require("webpack-parallel-uglify-plugin");

var _ = require("underscore");
var glob = require("glob");
var fs = require("fs");

var chevrotain = require("chevrotain");
var allTokens = require("./frontend/src/metabase/lib/expressions/tokens").allTokens;

function hasArg(arg) {
    var regex = new RegExp("^" + ((arg.length === 2) ? ("-w*"+arg[1]+"w*") : (arg)) + "$");
    return process.argv.filter(regex.test.bind(regex)).length > 0;
}

var SRC_PATH = __dirname + "/frontend/src/metabase";
var BUILD_PATH = __dirname + "/resources/frontend_client";

// default NODE_ENV to development
var NODE_ENV = process.env["NODE_ENV"] || "development";

var IS_WATCHING = hasArg("-w") || hasArg("--watch");
if (IS_WATCHING) {
    process.stderr.write("Warning: in webpack watch mode you must restart webpack if you change any CSS variables or custom media queries
");
}

// Babel:
var BABEL_CONFIG = {
    cacheDirectory: ".babel_cache"
};

// Build mapping of CSS variables
var CSS_SRC = glob.sync(SRC_PATH + "/css/**/*.css");
var CSS_MAPS = { vars: {}, media: {}, selector: {} };
CSS_SRC.map(webpackPostcssTools.makeVarMap).forEach(function(map) {
    for (var name in CSS_MAPS) _.extend(CSS_MAPS[name], map[name]);
});

// CSS Next:
var CSSNEXT_CONFIG = {
    features: {
        // pass in the variables and custom media we scanned for before
        customProperties: { variables: CSS_MAPS.vars },
        customMedia: { extensions: CSS_MAPS.media }
    },
    import: {
        path: ["resources/frontend_client/app/css"]
    },
    compress: false
};

var CSS_CONFIG = {
    localIdentName: NODE_ENV !== "production" ?
        "[name]__[local]___[hash:base64:5]" :
        "[hash:base64:5]",
    restructuring: false,
    compatibility: true,
    url: false, // disabled because we need to use relative url()
    importLoaders: 1
}

// happypack.config
var happyPackConfig = {
    plugins:[
        new HappyPack({
           id: "happyBabel",
           threads: 4,
           cache: true,
           loaders:[
               {
                   path: "babel",
                   query: BABEL_CONFIG
               }
           ]
        }),
        new HappyPack({
            id: "happyEslint",
            threads: 4,
            cache: true,
            loaders: ["eslint"]
        })
    ]
}

var config = module.exports = {
    context: SRC_PATH,
    entry: {
        "app-main": "./app-main.js",
        "app-public": "./app-public.js",
        "app-embed": "./app-embed.js",
        styles: "./css/index.css",
    },

    // output to "dist"
    output: {
        path: BUILD_PATH + "/app/dist",
        filename: "[name].bundle.js?[hash]",
        publicPath: "app/dist/"
    },

    module: {
        loaders: [
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules/,
                loader: "HappyPack/loader?id=happyBabel"
            },
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules|.spec.js/,
                loader: "HappyPack/loader?id=happyEslint"
            },
            {
                test: /.(eot|woff2?|ttf|svg|png)$/,
                loader: "file-loader"
            },
            {
                test: /.json$/,
                loader: "json-loader"
            },
            {
                test: /.css$/,
                loader: ExtractTextPlugin.extract("style-loader", "css-loader?" + JSON.stringify(CSS_CONFIG) + "!postcss-loader")
            }
        ]
    },

    resolve: {
        extensions: ["", ".webpack.js", ".web.js", ".js", ".jsx", ".css"],
        alias: {
            "metabase":             SRC_PATH,
            "style":                SRC_PATH + "/css/core/index.css",
            "ace":                  __dirname + "/node_modules/ace-builds/src-min-noconflict",
        }
    },

    plugins: [
        new UnusedFilesWebpackPlugin({
            globOptions: {
                ignore: [
                    "**/types/*.js",
                    "**/*.spec.*",
                    "**/__support__/*.js"
                ]
            }
        }),
        new webpack.DllReferencePlugin({
            context: __dirname,
            manifest: require("./manifest.json"),
            name:"vendors_dll"
        }),
        // Extracts initial CSS into a standard stylesheet that can be loaded in parallel with JavaScript
        // NOTE: the filename on disk won"t include "?[chunkhash]" but the URL in index.html generated by HtmlWebpackPlugin will:
        new ExtractTextPlugin("[name].bundle.css?[contenthash]"),
        new HtmlWebpackPlugin({
            filename: "../../index.html",
            chunks: ["app-main", "styles"],
            template: __dirname + "/resources/frontend_client/index_template.html",
            inject: "head",
            alwaysWriteToDisk: true,
        }),
        new HtmlWebpackPlugin({
            filename: "../../public.html",
            chunks: ["app-public", "styles"],
            template: __dirname + "/resources/frontend_client/index_template.html",
            inject: "head",
            alwaysWriteToDisk: true,
        }),
        new HtmlWebpackPlugin({
            filename: "../../embed.html",
            chunks: ["app-embed", "styles"],
            template: __dirname + "/resources/frontend_client/index_template.html",
            inject: "head",
            alwaysWriteToDisk: true,
        }),
        new AddAssetHtmlPlugin({
            filepath: BUILD_PATH + "/app/dist/*.dll.js",
            includeSourcemap: false
        }),
        new HtmlWebpackHarddiskPlugin({
            outputPath: __dirname + "/resources/frontend_client/app/dist"
        }),
        new webpack.DefinePlugin({
            "process.env": {
                NODE_ENV: JSON.stringify(NODE_ENV)
            }
        }),
        new BannerWebpackPlugin({
            chunks: {
                "app-main": {
                    beforeContent: "/*
* This file is subject to the terms and conditions defined in
 * file "LICENSE.txt", which is part of this source code package.
 */
",
                },
                "app-public": {
                    beforeContent: "/*
* This file is subject to the terms and conditions defined in
 * file "LICENSE.txt", which is part of this source code package.
 */
",
                },
                "app-embed": {
                    beforeContent: "/*
* This file is subject to the terms and conditions defined in
 * file "LICENSE-EMBEDDING.txt", which is part of this source code package.
 */
",
                },
            }
        }),
    ].concat(happyPackConfig.plugins),

    postcss: function (webpack) {
        return [
            require("postcss-import")(),
            require("postcss-url")(),
            require("postcss-cssnext")(CSSNEXT_CONFIG)
        ]
    }
};

if (NODE_ENV === "hot") {
    // suffixing with ".hot" allows us to run both `yarn run build-hot` and `yarn run test` or `yarn run test-watch` simultaneously
    config.output.filename = "[name].hot.bundle.js?[hash]";

    // point the publicPath (inlined in index.html by HtmlWebpackPlugin) to the hot-reloading server
    config.output.publicPath = "http://localhost:8080/" + config.output.publicPath;

    config.module.loaders.unshift({
        test: /.jsx$/,
        exclude: /node_modules/,
        loaders: ["react-hot", "babel?"+JSON.stringify(BABEL_CONFIG)]
    });

    // disable ExtractTextPlugin
    config.module.loaders[config.module.loaders.length - 1].loader = "style-loader!css-loader?" + JSON.stringify(CSS_CONFIG) + "!postcss-loader"

    config.devServer = {
        hot: true,
        inline: true,
        contentBase: "frontend"
    };

    config.plugins.unshift(
        new webpack.NoErrorsPlugin(),
        new webpack.HotModuleReplacementPlugin()
    );
}

if (NODE_ENV !== "production") {
    // replace minified files with un-minified versions
    for (var name in config.resolve.alias) {
        var minified = config.resolve.alias[name];
        var unminified = minified.replace(/[.-/]min/g, "");
        if (minified !== unminified && fs.existsSync(unminified)) {
            config.resolve.alias[name] = unminified;
        }
    }

    // enable "cheap" source maps in hot or watch mode since re-build speed overhead is < 1 second
    config.devtool = "cheap-module-source-map";
    config.output.devtoolModuleFilenameTemplate = "[absolute-resource-path]";
    config.output.pathinfo = true;
} else {
    config.plugins.push(new ParallelUglifyPlugin({
        uglifyJs:{
            compress: {
                warnings: false,
            },
            output: {
                comments: false,
            },
            mangle: {
                except: allTokens.map(function(currTok) {
                    return chevrotain.tokenName(currTok);
                })
            }
        },
        cacheDir: ".js-cache"
    }))

    config.devtool = "source-map";
}

webpack編譯緩慢一直是現代化前端開發的一個痛點。社區中很多優秀的開發者都貢獻出非常多的插件來視圖解決這個問題。下面就將本文中用到的插件拋出，在下面這幾個插件的配合下，編譯速度會得到顯著的提升。

happypack: 讓loader以多進程去處理文件，借助緩存機制，可以在rebuild的時候更快

webpack.DllPlugin: 優先構建npm的第三方包

webpack.DllReferencePlugin: 只負責用來引用由webpack.DllPlugin生成的第三方依賴項

webpack-parallel-uglify-plugin: 并行壓縮javascript文件(生產環境中使用，可以顯著的提升構建速度)

下面就對這些插件以及我踩下的坑進行一個簡單的介紹。

https://github.com/amireh/happypack

happypack允許webpack并行編譯多個文件來提升構建速度。但是在某些情況下，其提升的效果并不是十分明顯，這個時候就需要看一下自己電腦的cpu占用率，以及進程的運行情況。

happypack作為webpack的一個插件，所以在使用之前應該先安裝。

yarn add happywebpack -D

配置過程很簡單，只需要在plugins選項中創建其實例，可以創建一個或多個，然后在loader中引用即可。只需要注意一點，當創建多個happypack的實例的時候，給每個實例傳遞一個id參數。基本的變動如下：

原配置文件

// 省略了部分的配置文件
var config = module.exports = {
    //................
    module: {
        loaders: [
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules/,
                loader: "babel",
                query: BABEL_CONFIG
            },
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules|.spec.js/,
                loader: "eslint"
            },
            {
                test: /.(eot|woff2?|ttf|svg|png)$/,
                loader: "file-loader"
            },
            {
                test: /.json$/,
                loader: "json-loader"
            },
            {
                test: /.css$/,
                loader: ExtractTextPlugin.extract("style-loader", "css-loader?" + JSON.stringify(CSS_CONFIG) + "!postcss-loader")
            }
        ]
    }
    //...............
}

改動如下

// happypack.config：更多的配置可以參考文檔，按需索取。
var happyPackConfig = {
    plugins:[
        new HappyPack({
           id: "happyBabel",
           threads: 4,
           cache: true,
           loaders:[
               {
                   path: "babel",
                   query: BABEL_CONFIG
               }
           ]
        }),
        new HappyPack({
            id: "happyEslint",
            threads: 4,
            cache: true,
            loaders: ["eslint"]
        })
    ]
}
var config = module.exports = {
    //................
    module: {
        loaders: [
            // 變動這兩個
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules/,
                loader: "HappyPack/loader?id=happyBabel"
            },
            {
                test: /.(js|jsx)$/,
                exclude: /node_modules|.spec.js/,
                loader: "HappyPack/loader?id=happyEslint"
            },
            // 其它的并未改動
            {
                test: /.(eot|woff2?|ttf|svg|png)$/,
                loader: "file-loader"
            },
            {
                test: /.json$/,
                loader: "json-loader"
            },
            {
                test: /.css$/,
                loader: ExtractTextPlugin.extract("style-loader", "css-loader?" + JSON.stringify(CSS_CONFIG) + "!postcss-loader")
            }
        ]
    }
    //...............
}
// 在module.loader中引用

然后，當我們運行：

yarn run build

就會看到如下輸出：

大概意思就是，happupack的版本是3.1.0，對babel-loader開啟了四個線程并從緩存中加載了627個模塊。

這兩個插件在使用的時候，還是有幾個小坑的，下面就會為大家講述幾個。

先說一下基本的用法，官方推薦在使用的時候，我們需要寫兩個webpack配置文件。其中一個配置文件主要用于webpack.DllPlugin插件進行第三方的預打包，另一個則是主webpack配置文件，在其中使用webpack.DllReferencePlugin插件引用第三方生成的依賴模塊。

所以，我們其中一個配置文件可以命名如下：ddl.config.js

const webpack = require("webpack")
const vendors = Object.keys(require("package.json")["dependencies"])
const SRC_PATH = __dirname + "/frontend/src/metabase"
const BUILD_PATH = __dirname + "/resources/frontend_client"

module.exports = {
  output: {
    path: BUILD_PATH + "/app/dist",
    filename: "[name].dll.js",
    library: "[name]_dll",
  },
  entry: {
    // 第三方依賴設置為打包的入口
    vendors: vendors,
  },
  plugins: [
    new webpack.DllPlugin({
      path: "manifest.json",
      name: "[name]_dll",
      context: __dirname,
    }),
  ],
}

接下來，在我們進行webpack的正式打包之前可以先來一個預打包，運行如下命令：

webpack --config ddl.donfig.js

命令結束之后，我們可以在BUILD_PATH下面生成了一個vendors.dll.js(具體的名稱根據你的配置而來)以及根目錄下面的manifset.json文件。打開這個文件，可以看到webpack.DllPlugin插件為每個第三方包都生成了一個唯一的全局id。

上面的這個插件的配置有幾個需要注意的地方，output.library屬性是必須的，同時webpack.DllPlugin參數對象的name屬性和其保持一致。更詳細的配置可以參考文檔。

預打包之后，我們需要對我們的主webpack.config.js文件做如下改動。

//..........................
    plugins:[
        // ........
        new webpack.DllReferencePlugin({
            context: __dirname,
            manifest: require("./manifest.json"),
            // 上述生成的文件的名稱
            name:"vendors_dll"
        }),
        //.........
    ]
//..........................

配置很簡單，詳細的配置小伙伴可以參考文檔按需索取。這里有幾個需要注意的地方給大家說明一下。

vendors.dll.js文件一定要在引入我們的html文件中，而且在引入模塊文件之前引入，否則你會看到這個錯誤。

(騷年，有沒有覺得菊花一緊)

但是，有些情況下，我們使用的是html-webpack-plugin來動態創建我們的html模板，這個時候我們怎么把生成的vendors.dll.js引入到我們的頁面中呢？路徑可以寫死，但是你試試，反正我遇到了這個錯誤。如果你的可以，歡迎在github上留言交流。

當你遇到這個錯誤，別灰心，接著找解決方法。原來，還真有，就是下面即將介紹的這個插件：add-asset-html-webpack-plugin

。這個插件的主要作用就是將我們自己的靜態文件插入到模版生成的html文件中。所以需要對webpack.config.js作出如下的改動。

var AddAssetHtmlPlugin = require("add-asset-html-webpack-plugin");
//..........................
    plugins:[
        // ........
       new AddAssetHtmlPlugin({
            filepath: BUILD_PATH + "/app/dist/*.dll.js",
            includeSourcemap: false
        }),
        //.........
    ]
//..........................

includeSourcemap選項如果不配置的話，可能會遇到vendors.dll.js.map cannot found的錯誤

然后，運行，bingo。至此，打包時間已經從100s左右降到了35s左右。恭喜恭喜。

https://github.com/gdborton/webpack-parallel-uglify-plugin

這個插件的用處十分的強大，并行壓縮javascript，配置也十分簡單，參考官方文檔就能知道怎么使用，如我們的配置文件就做了如下的變動。

原js文件

config.plugins.push(new webpack.optimize.UglifyJsPlugin({
    // suppress uglify warnings in production
    // output from these warnings was causing Heroku builds to fail (#5410)
    compress: {
        warnings: false,
    },
    output: {
        comments: false,
    },
    mangle: {
        // this is required to ensure we don"t minify Chevrotain token identifiers
        // https://github.com/SAP/chevrotain/tree/master/examples/parser/minification
        except: allTokens.map(function(currTok) {
            return chevrotain.tokenName(currTok);
        })
    }
}))

變動后

config.plugins.push(new ParallelUglifyPlugin({
        uglifyJs:{
            compress: {
                warnings: false,
            },
            output: {
                comments: false,
            },
            mangle: {
                // this is required to ensure we don"t minify Chevrotain token identifiers
                // https://github.com/SAP/chevrotain/tree/master/examples/parser/minification
                except: allTokens.map(function(currTok) {
                    return chevrotain.tokenName(currTok);
                })
            }
        },
        cacheDir: ".js-cache"
    }))

至此，我們大部分的優化的內容已經完成，下面是我們打包時間的一個對比。
優化前打包時間

優化后打包時間

除了上述的幾個可以優化的地方，還有很多一些小點可以進行優化，比如：

css-loader在0.15.0之后的版本打包時間明顯增長

我們也可以適當的縮短一下模塊的查詢路徑等

如果你有好的優化點，歡迎在我的github留言交流哈！！！