How can I use webpack with express?

It can be realized by specifying "node" to "target" option, since v1.10.2.

For reference: http://jlongster.com/Backend-Apps-with-Webpack--Part-I

If you want to bundle the server and the client's code at the same time, it is possible to use multiple configuration in the following manner.

// webpack.config.js

module.exports = [
    {
        name: 'server',
        entry: './src/server/index.js',
        target: 'node',
        output: {
            path: __dirname + '/dist/server',
            filename: 'bundle.js',
        },
    },
    {
        name: 'client',
        entry: './src/client/index.js',
        // target: 'web', // by default
        output: {
            path: __dirname + '/dist/client',
            filename: 'bundle.js',
        },
    }
];

I am just clarifying @meta2's answer because I believe it can be written in a more understandable way - although full points to him!

tl;dr - set target: 'node' in your webpack.config.js to fix the errors that get generated when using Webpack with Express.

You still get warnings like:

WARNING in ./node_modules/express/lib/view.js 
81:13-25 Critical dependency: the request of a dependency is an expression

To fix those, use https://github.com/liady/webpack-node-externals. FYI - this reduces you bundle size significantly (check size before and after) and speeds up the bundling time incredibly.

Full example:

const path = require('path')
const nodeExternals = require('webpack-node-externals')

module.exports = {
  entry: './src/app.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'dist')
  },
  target: 'node',   // THIS IS THE IMPORTANT PART
  externals: [nodeExternals()],
  mode: 'development'
}

What I ended up doing was I used 2 different configurations, 1 for packing the server stuff together using webpack, and 1 for packing all the browser stuff together and also run webpack dev server for hot reloading.

Server webpack config aka webpack.node.config.js now looks like this:

var webpack = require('webpack');
var path = require('path');
var fs = require('fs');
var nodeModules = {};

// note the path.resolve(__dirname, ...) part
// without it, eslint-import-resolver-webpack fails
// since eslint might be invoked with different cwd
fs.readdirSync(path.resolve(__dirname, 'node_modules'))
    .filter(x => ['.bin'].indexOf(x) === -1)
    .forEach(mod => { nodeModules[mod] = `commonjs ${mod}`; });

// es5 style alternative
// fs.readdirSync(path.resolve(__dirname, 'node_modules'))
//     .filter(function(x) {
//         return ['.bin'].indexOf(x) === -1;
//     })
//     .forEach(function(mod) {
//         nodeModules[mod] = 'commonjs ' + mod;    
//     });

module.exports =

{
    // The configuration for the server-side rendering
    name: 'server',
    target: 'node',
    entry: './app/server/serverEntryPrototype.js',
    output: {
        path: './bin/',
        publicPath: 'bin/',
        filename: 'serverEntryPoint.js'
    },
    externals: nodeModules,
    module: {
        loaders: [
            { test: /\.js$/,

                loaders: [
                    // 'imports?document=this',

                    // 'react-hot',
                    'babel-loader'
                    //,'jsx-loader'
                ]
            },
            { test:  /\.json$/, loader: 'json-loader' },
        ]
    },
    plugins: [
    // new webpack.NormalModuleReplacementPlugin("^(react-bootstrap-modal)$", "^(react)$")
    // new webpack.IgnorePlugin(new RegExp("^(react-bootstrap-modal)$"))
    // new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/)
  ]
};

Browser webpack config aka webpack.browser.config.js now looks like this:

var webpack = require('webpack');
var path = require('path');
var buildPath = path.resolve(__dirname, 'assets');
var fs = require('fs');


var commonLoaders = [
    { test: /\.js$/,

        loaders: [
            'react-hot',
            'babel-loader'
            //,'jsx-loader'
        ]
    }
];


module.exports =
{
    // Makes sure errors in console map to the correct file
    // and line number
    name: 'browser',
    devtool: 'eval',
    entry: [
        //'./bin/www.js',
        './app/index.js',
        'webpack/hot/dev-server',
        'webpack-dev-server/client?http://localhost:8081'  // WebpackDevServer host and port
    ],
    output: {
        path: buildPath,
        filename: '[name].js',
        // Everything related to Webpack should go through a build path,
        // localhost:3000/build. That makes proxying easier to handle
        publicPath: 'http://localhost:8081/assets/'
    },

    extensions: [
        '',
        '.jsx', '.js',
        '.json',
        '.html',
        '.css', '.styl', '.scss', '.sass'
    ],

    module: {

        loaders: [
            // Compile es6 to js.
            {
                test: /app\/.*\.jsx?$/,
                loaders: [
                    'react-hot',
                    'babel-loader'
                ]
            },

            ///app\/.*\.json$/
            { test:  /\.json$/, loader: 'json-loader' },

            // Styles
            { test: /\.css$/, loader: 'style-loader!css-loader' },
            { test: /\.s(a|c)ss$/, loader: 'style!css?localIdentName=[path][name]---[local]---[hash:base64:5]!postcss!sass' },

            // Fonts
            { test: /\.woff(2)?(\?v=[0-9]\.[0-9]\.[0-9])?$/, loader: 'url-loader?limit=10000&minetype=application/font-woff' },
            { test: /\.(ttf|eot|svg)(\?v=[0-9]\.[0-9]\.[0-9])?$/, loader: 'file-loader' }

            //{ test: /\.png$/, loader: 'url-loader?limit=100000' },
            //{ test: /\.jpg$/, loader: 'file-loader' }
        ],

        plugins: [
            new webpack.HotModuleReplacementPlugin(),
            new webpack.NoErrorsPlugin()
        ]
    },

    postcss: [
        require('autoprefixer-core')
    ],

    devtool: 'source-map'
}
;