Webpack Cheatsheet¶

Webpack - Static Module Bundler

Webpack is a static module bundler for modern JavaScript applications. When webpack processes your application, it internally builds a dependency graph from one or more entry points and then combines every module your project needs into one or more bundles.

Table of Contents¶

Installation
Basic Configuration
Entry Points
Output
Loaders
Plugins
Mode
Development Server
Code Splitting
Optimization
Module Resolution
Hot Module Replacement
Environment Variables
Production Build
Advanced Configuration
Performance
Troubleshooting
Best Practices

Installation¶

Global Installation¶

# Install webpack globally
npm install -g webpack webpack-cli

# Check version
webpack --version

Local Installation (Recommended)¶

# Initialize npm project
npm init -y

# Install webpack locally
npm install --save-dev webpack webpack-cli

# Install webpack dev server
npm install --save-dev webpack-dev-server

# Install common loaders and plugins
npm install --save-dev html-webpack-plugin css-loader style-loader file-loader url-loader

Package.json Scripts¶

{
  "scripts": {
    "build": "webpack --mode production",
    "dev": "webpack --mode development",
    "start": "webpack serve --mode development",
    "watch": "webpack --mode development --watch"
  }
}

Basic Configuration¶

Minimal webpack.config.js¶

const path = require('path');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

Complete Basic Configuration¶

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'bundle.[contenthash].js',
    path: path.resolve(__dirname, 'dist'),
    clean: true
  },
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: ['style-loader', 'css-loader']
      },
      {
        test: /\.(png|svg|jpg|jpeg|gif)$/i,
        type: 'asset/resource'
      }
    ]
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: './src/index.html'
    })
  ]
};

TypeScript Configuration¶

const path = require('path');

module.exports = {
  entry: './src/index.ts',
  module: {
    rules: [
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/
      }
    ]
  },
  resolve: {
    extensions: ['.tsx', '.ts', '.js']
  },
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

Entry Points¶

Single Entry Point¶

module.exports = {
  entry: './src/index.js'
};

Multiple Entry Points¶

module.exports = {
  entry: {
    main: './src/index.js',
    vendor: './src/vendor.js'
  }
};

Dynamic Entry Points¶

module.exports = {
  entry: () => {
    return {
      main: './src/index.js',
      admin: './src/admin.js'
    };
  }
};

Entry with Dependencies¶

module.exports = {
  entry: {
    main: {
      import: './src/index.js',
      dependOn: 'shared'
    },
    admin: {
      import: './src/admin.js',
      dependOn: 'shared'
    },
    shared: 'lodash'
  }
};

Output¶

Basic Output Configuration¶

const path = require('path');

module.exports = {
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

Multiple Entry Output¶

module.exports = {
  entry: {
    main: './src/index.js',
    admin: './src/admin.js'
  },
  output: {
    filename: '[name].bundle.js',
    path: path.resolve(__dirname, 'dist')
  }
};

Output with Hashing¶

module.exports = {
  output: {
    filename: '[name].[contenthash].js',
    path: path.resolve(__dirname, 'dist'),
    clean: true
  }
};

Public Path Configuration¶

module.exports = {
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist'),
    publicPath: '/assets/'
  }
};

Library Output¶

module.exports = {
  output: {
    filename: 'my-library.js',
    path: path.resolve(__dirname, 'dist'),
    library: {
      name: 'MyLibrary',
      type: 'umd'
    }
  }
};

Loaders¶

CSS Loaders¶

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: ['style-loader', 'css-loader']
      },
      {
        test: /\.s[ac]ss$/i,
        use: ['style-loader', 'css-loader', 'sass-loader']
      },
      {
        test: /\.less$/i,
        use: ['style-loader', 'css-loader', 'less-loader']
      }
    ]
  }
};

JavaScript Loaders¶

module.exports = {
  module: {
    rules: [
      {
        test: /\.m?js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: ['@babel/preset-env']
          }
        }
      },
      {
        test: /\.tsx?$/,
        use: 'ts-loader',
        exclude: /node_modules/
      }
    ]
  }
};

File Loaders¶

module.exports = {
  module: {
    rules: [
      {
        test: /\.(png|svg|jpg|jpeg|gif)$/i,
        type: 'asset/resource'
      },
      {
        test: /\.(woff|woff2|eot|ttf|otf)$/i,
        type: 'asset/resource'
      },
      {
        test: /\.(csv|tsv)$/i,
        use: ['csv-loader']
      },
      {
        test: /\.xml$/i,
        use: ['xml-loader']
      }
    ]
  }
};

Asset Modules¶

module.exports = {
  module: {
    rules: [
      {
        test: /\.png/,
        type: 'asset/resource'
      },
      {
        test: /\.html/,
        type: 'asset/resource'
      },
      {
        test: /\.txt/,
        type: 'asset/source'
      },
      {
        test: /\.jpg/,
        type: 'asset',
        parser: {
          dataUrlCondition: {
            maxSize: 4 * 1024 // 4kb
          }
        }
      }
    ]
  }
};

Loader Options¶

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [
          'style-loader',
          {
            loader: 'css-loader',
            options: {
              modules: true,
              sourceMap: true
            }
          }
        ]
      }
    ]
  }
};

Plugins¶

HTML Webpack Plugin¶

const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  plugins: [
    new HtmlWebpackPlugin({
      template: './src/index.html',
      filename: 'index.html',
      inject: 'body'
    })
  ]
};

Extract CSS Plugin¶

const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  module: {
    rules: [
      {
        test: /\.css$/i,
        use: [MiniCssExtractPlugin.loader, 'css-loader']
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      filename: '[name].[contenthash].css'
    })
  ]
};

Define Plugin¶

const webpack = require('webpack');

module.exports = {
  plugins: [
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify('production'),
      'process.env.API_URL': JSON.stringify('https://api.example.com')
    })
  ]
};

Copy Webpack Plugin¶

const CopyWebpackPlugin = require('copy-webpack-plugin');

module.exports = {
  plugins: [
    new CopyWebpackPlugin({
      patterns: [
        { from: 'public', to: 'public' },
        { from: 'assets/images', to: 'images' }
      ]
    })
  ]
};

Bundle Analyzer Plugin¶

const BundleAnalyzerPlugin = require('webpack-bundle-analyzer').BundleAnalyzerPlugin;

module.exports = {
  plugins: [
    new BundleAnalyzerPlugin({
      analyzerMode: 'static',
      openAnalyzer: false
    })
  ]
};

Clean Webpack Plugin¶

const { CleanWebpackPlugin } = require('clean-webpack-plugin');

module.exports = {
  plugins: [
    new CleanWebpackPlugin()
  ]
};

Mode¶

Development Mode¶

module.exports = {
  mode: 'development',
  devtool: 'eval-source-map'
};

Production Mode¶

module.exports = {
  mode: 'production',
  devtool: 'source-map'
};

Mode-specific Configuration¶

module.exports = (env, argv) => {
  const isProduction = argv.mode === 'production';

  return {
    mode: argv.mode,
    devtool: isProduction ? 'source-map' : 'eval-source-map',
    optimization: {
      minimize: isProduction
    }
  };
};

Development Server¶

Basic Dev Server¶

module.exports = {
  devServer: {
    static: './dist',
    port: 3000,
    open: true
  }
};

Advanced Dev Server Configuration¶

module.exports = {
  devServer: {
    static: {
      directory: path.join(__dirname, 'dist')
    },
    compress: true,
    port: 3000,
    hot: true,
    open: true,
    historyApiFallback: true,
    proxy: {
      '/api': {
        target: 'http://localhost:8080',
        changeOrigin: true,
        pathRewrite: {
          '^/api': ''
        }
      }
    }
  }
};

HTTPS Dev Server¶

module.exports = {
  devServer: {
    https: true,
    // or with custom certificates
    https: {
      key: fs.readFileSync('/path/to/server.key'),
      cert: fs.readFileSync('/path/to/server.crt'),
      ca: fs.readFileSync('/path/to/ca.pem')
    }
  }
};

Code Splitting¶

Entry Point Splitting¶

module.exports = {
  entry: {
    main: './src/index.js',
    vendor: './src/vendor.js'
  }
};

Dynamic Imports¶

// In your JavaScript code
import('./math.js').then(math => {
  console.log(math.add(16, 26));
});

// Or with async/await
async function loadMath() {
  const math = await import('./math.js');
  return math.add(16, 26);
}

SplitChunks Plugin¶

module.exports = {
  optimization: {
    splitChunks: {
      chunks: 'all',
      cacheGroups: {
        vendor: {
          test: /[\\/]node_modules[\\/]/,
          name: 'vendors',
          chunks: 'all'
        },
        common: {
          name: 'common',
          minChunks: 2,
          chunks: 'all',
          enforce: true
        }
      }
    }
  }
};

Advanced Code Splitting¶

module.exports = {
  optimization: {
    splitChunks: {
      chunks: 'all',
      minSize: 20000,
      maxSize: 244000,
      cacheGroups: {
        default: {
          minChunks: 2,
          priority: -20,
          reuseExistingChunk: true
        },
        vendor: {
          test: /[\\/]node_modules[\\/]/,
          priority: -10,
          reuseExistingChunk: true
        },
        react: {
          test: /[\\/]node_modules[\\/](react|react-dom)[\\/]/,
          name: 'react',
          chunks: 'all'
        }
      }
    }
  }
};

Optimization¶

Minification¶

const TerserPlugin = require('terser-webpack-plugin');

module.exports = {
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          compress: {
            drop_console: true
          }
        }
      })
    ]
  }
};

CSS Optimization¶

const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');

module.exports = {
  optimization: {
    minimizer: [
      new CssMinimizerPlugin()
    ]
  }
};

Tree Shaking¶

module.exports = {
  mode: 'production',
  optimization: {
    usedExports: true,
    sideEffects: false
  }
};

Runtime Chunk¶

module.exports = {
  optimization: {
    runtimeChunk: 'single'
  }
};

Module Concatenation¶

module.exports = {
  optimization: {
    concatenateModules: true
  }
};

Module Resolution¶

Resolve Configuration¶

const path = require('path');

module.exports = {
  resolve: {
    extensions: ['.js', '.jsx', '.ts', '.tsx', '.json'],
    alias: {
      '@': path.resolve(__dirname, 'src'),
      'components': path.resolve(__dirname, 'src/components'),
      'utils': path.resolve(__dirname, 'src/utils')
    },
    modules: [
      'node_modules',
      path.resolve(__dirname, 'src')
    ]
  }
};

Resolve Fallback¶

module.exports = {
  resolve: {
    fallback: {
      "fs": false,
      "path": require.resolve("path-browserify"),
      "crypto": require.resolve("crypto-browserify")
    }
  }
};

Hot Module Replacement¶

Enable HMR¶

const webpack = require('webpack');

module.exports = {
  devServer: {
    hot: true
  },
  plugins: [
    new webpack.HotModuleReplacementPlugin()
  ]
};

HMR in Code¶

// In your JavaScript modules
if (module.hot) {
  module.hot.accept('./library.js', function() {
    console.log('Accepting the updated library module!');
    // Re-render or update your app
  });
}

React Hot Reload¶

const ReactRefreshWebpackPlugin = require('@pmmmwh/react-refresh-webpack-plugin');

module.exports = {
  module: {
    rules: [
      {
        test: /\.[jt]sx?$/,
        exclude: /node_modules/,
        use: [
          {
            loader: 'babel-loader',
            options: {
              plugins: ['react-refresh/babel']
            }
          }
        ]
      }
    ]
  },
  plugins: [
    new ReactRefreshWebpackPlugin()
  ]
};

Environment Variables¶

DefinePlugin for Environment Variables¶

const webpack = require('webpack');

module.exports = {
  plugins: [
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV),
      'process.env.API_URL': JSON.stringify(process.env.API_URL || 'http://localhost:3000')
    })
  ]
};

Environment-specific Configuration¶

module.exports = (env, argv) => {
  const isProduction = argv.mode === 'production';

  return {
    mode: argv.mode,
    plugins: [
      new webpack.DefinePlugin({
        'process.env.NODE_ENV': JSON.stringify(argv.mode),
        'process.env.API_URL': JSON.stringify(
          isProduction ? 'https://api.production.com' : 'http://localhost:3000'
        )
      })
    ]
  };
};

DotEnv Plugin¶

const Dotenv = require('dotenv-webpack');

module.exports = {
  plugins: [
    new Dotenv({
      path: './.env',
      safe: true,
      systemvars: true
    })
  ]
};

Production Build¶

Production Configuration¶

const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');
const CssMinimizerPlugin = require('css-minimizer-webpack-plugin');
const TerserPlugin = require('terser-webpack-plugin');

module.exports = {
  mode: 'production',
  entry: './src/index.js',
  output: {
    filename: '[name].[contenthash].js',
    path: path.resolve(__dirname, 'dist'),
    clean: true
  },
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader',
          options: {
            presets: ['@babel/preset-env']
          }
        }
      },
      {
        test: /\.css$/,
        use: [MiniCssExtractPlugin.loader, 'css-loader']
      }
    ]
  },
  plugins: [
    new HtmlWebpackPlugin({
      template: './src/index.html',
      minify: {
        removeComments: true,
        collapseWhitespace: true,
        removeRedundantAttributes: true,
        useShortDoctype: true,
        removeEmptyAttributes: true,
        removeStyleLinkTypeAttributes: true,
        keepClosingSlash: true,
        minifyJS: true,
        minifyCSS: true,
        minifyURLs: true
      }
    }),
    new MiniCssExtractPlugin({
      filename: '[name].[contenthash].css'
    })
  ],
  optimization: {
    minimize: true,
    minimizer: [
      new TerserPlugin({
        terserOptions: {
          compress: {
            drop_console: true
          }
        }
      }),
      new CssMinimizerPlugin()
    ],
    splitChunks: {
      chunks: 'all',
      cacheGroups: {
        vendor: {
          test: /[\\/]node_modules[\\/]/,
          name: 'vendors',
          chunks: 'all'
        }
      }
    },
    runtimeChunk: 'single'
  }
};

Build Scripts¶

{
  "scripts": {
    "build": "webpack --mode production",
    "build:analyze": "webpack --mode production --env analyze",
    "build:stats": "webpack --mode production --json > stats.json"
  }
}

Advanced Configuration¶

Multi-page Application¶

const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  entry: {
    home: './src/home.js',
    about: './src/about.js',
    contact: './src/contact.js'
  },
  plugins: [
    new HtmlWebpackPlugin({
      filename: 'home.html',
      template: './src/home.html',
      chunks: ['home']
    }),
    new HtmlWebpackPlugin({
      filename: 'about.html',
      template: './src/about.html',
      chunks: ['about']
    }),
    new HtmlWebpackPlugin({
      filename: 'contact.html',
      template: './src/contact.html',
      chunks: ['contact']
    })
  ]
};

Micro-frontends Configuration¶

const ModuleFederationPlugin = require('@module-federation/webpack');

module.exports = {
  plugins: [
    new ModuleFederationPlugin({
      name: 'shell',
      remotes: {
        mfe1: 'mfe1@http://localhost:3001/remoteEntry.js',
        mfe2: 'mfe2@http://localhost:3002/remoteEntry.js'
      }
    })
  ]
};

Progressive Web App¶

const WorkboxPlugin = require('workbox-webpack-plugin');

module.exports = {
  plugins: [
    new WorkboxPlugin.GenerateSW({
      clientsClaim: true,
      skipWaiting: true
    })
  ]
};

Custom Loaders¶

// custom-loader.js
module.exports = function(source) {
  // Transform the source
  return `export default ${JSON.stringify(source)}`;
};

// webpack.config.js
module.exports = {
  module: {
    rules: [
      {
        test: /\.custom$/,
        use: path.resolve(__dirname, 'custom-loader.js')
      }
    ]
  }
};

Custom Plugins¶

class MyCustomPlugin {
  apply(compiler) {
    compiler.hooks.emit.tapAsync('MyCustomPlugin', (compilation, callback) => {
      console.log('This is an example plugin!');
      callback();
    });
  }
}

module.exports = {
  plugins: [
    new MyCustomPlugin()
  ]
};

Performance¶

Performance Budgets¶

module.exports = {
  performance: {
    maxAssetSize: 250000,
    maxEntrypointSize: 250000,
    hints: 'warning'
  }
};

Lazy Loading¶

// Dynamic imports for lazy loading
const LazyComponent = React.lazy(() => import('./LazyComponent'));

// Webpack magic comments
import(
  /* webpackChunkName: "my-chunk-name" */
  /* webpackMode: "lazy" */
  './modules/my-module.js'
);

Prefetching and Preloading¶

// Prefetch
import(
  /* webpackPrefetch: true */
  './modules/LoginModal.js'
);

// Preload
import(
  /* webpackPreload: true */
  './modules/ChartingLibrary.js'
);

Bundle Analysis¶

# Generate stats file
webpack --profile --json > stats.json

# Analyze with webpack-bundle-analyzer
npx webpack-bundle-analyzer stats.json

# Use webpack-bundle-analyzer plugin
npm install --save-dev webpack-bundle-analyzer

Troubleshooting¶

Common Issues and Solutions¶

Module Not Found¶

// Check resolve configuration
module.exports = {
  resolve: {
    extensions: ['.js', '.jsx', '.ts', '.tsx'],
    alias: {
      '@': path.resolve(__dirname, 'src')
    }
  }
};

Memory Issues¶

# Increase Node.js memory limit
node --max-old-space-size=4096 node_modules/.bin/webpack

# Or in package.json
{
  "scripts": {
    "build": "node --max-old-space-size=4096 node_modules/.bin/webpack"
  }
}

Slow Build Times¶

module.exports = {
  // Use cache
  cache: {
    type: 'filesystem'
  },

  // Exclude node_modules from babel-loader
  module: {
    rules: [
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: 'babel-loader'
      }
    ]
  },

  // Use thread-loader for expensive loaders
  module: {
    rules: [
      {
        test: /\.js$/,
        use: [
          'thread-loader',
          'babel-loader'
        ]
      }
    ]
  }
};

Source Map Issues¶

module.exports = {
  // Different source map options
  devtool: 'eval-source-map', // Development
  devtool: 'source-map', // Production
  devtool: 'cheap-module-source-map', // Faster builds
  devtool: false // No source maps
};

Debugging Configuration¶

module.exports = {
  stats: {
    colors: true,
    modules: false,
    children: false,
    chunks: false,
    chunkModules: false
  }
};

Best Practices¶

Configuration Organization¶

// webpack.common.js
const path = require('path');
const HtmlWebpackPlugin = require('html-webpack-plugin');

module.exports = {
  entry: './src/index.js',
  plugins: [
    new HtmlWebpackPlugin({
      template: './src/index.html'
    })
  ]
};

// webpack.dev.js
const { merge } = require('webpack-merge');
const common = require('./webpack.common.js');

module.exports = merge(common, {
  mode: 'development',
  devtool: 'eval-source-map',
  devServer: {
    static: './dist'
  }
});

// webpack.prod.js
const { merge } = require('webpack-merge');
const common = require('./webpack.common.js');

module.exports = merge(common, {
  mode: 'production',
  devtool: 'source-map'
});

Performance Optimization¶

Use production mode for optimizations
Enable tree shaking to remove dead code
Split chunks to improve caching
Use content hashing for long-term caching
Minimize bundle size with proper loaders and plugins

Development Experience¶

Use HMR for faster development
Configure source maps for debugging
Set up dev server with proxy for API calls
Use webpack-bundle-analyzer to understand bundle composition

Code Organization¶

Separate configuration for different environments
Use aliases for cleaner imports
Organize loaders by file type
Group related plugins together

Summary¶

Webpack is a powerful and flexible module bundler that can handle complex build requirements for modern web applications. Key features include:

Module Bundling: Combines modules into optimized bundles
Loaders: Transform files during the build process
Plugins: Extend webpack functionality
Code Splitting: Split code into smaller chunks for better performance
Hot Module Replacement: Update modules without full page reload
Tree Shaking: Remove unused code from bundles
Asset Management: Handle various file types and assets

By mastering webpack configuration and following best practices, you can create efficient build processes that improve both development experience and application performance.