webpack.config.dev.js

const webpack = require('webpack');
const path = require('path');

module.exports = {
  entry: {
    app: ['webpack/hot/dev-server', './scripts/app.js']
  },

  output: {
    filename: 'bundle.js',
    publicPath: `/dist/`
  },

  devServer: {
    contentBase: path.join(__dirname, 'public'),
    publicPath: '/dist/'
  },

  module: {
    rules: [
        {
            test: /\.jsx?$/,
            enforce: "pre",
            loader: "eslint-loader",
            exclude: /node_modules/
        },
        {
            test: /\.jsx?$/,
            loader: 'babel-loader',
            exclude: /node_modules/,
            query: {
                presets: ['react', 'es2015', 'stage-3']
            }
        },
        { test: /\.css$/, loader: 'style-loader!css-loader' },
        { test: /\.scss$/, loader: 'style-loader!css-loader!sass-loader'},
        { test: /\.(ttf|eot|otf|svg)(\?v=[0-9]\.[0-9]\.[0-9])?$/, loader: "file-loader" },
    ],
  },

  plugins: [
    new webpack.HotModuleReplacementPlugin(),
    new webpack.IgnorePlugin(new RegExp("^(fs|ipc)$")),
    new webpack.LoaderOptionsPlugin({
        options: {
            eslint: {
                failOnWarning: false,
                failOnError: true
            }
        }
    }),
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV || 'development'),
    }),
  ]
}

webpack.config.prod.js

const webpack = require('webpack');
const path = require('path');

module.exports = {
  entry: ['babel-polyfill', './main.js'],
  
  output: {
    path: __dirname,
    filename: './main.prod.js'
  },

  // this is the same as webpack.config.dev.js and everything below (except the environment default)
  module: {
    rules: [
        {
            test: /\.jsx?$/,
            enforce: "pre",
            loader: "eslint-loader",
            exclude: /node_modules/
        },
        {
            test: /\.jsx?$/,
            loader: 'babel-loader',
            exclude: /node_modules/,
            query: {
                presets: ['react', 'es2015', 'stage-3']
            }
        },
        { test: /\.css$/, loader: 'style-loader!css-loader' },
        { test: /\.scss$/, loader: 'style-loader!css-loader!sass-loader'},
        { test: /\.(ttf|eot|otf|svg)(\?v=[0-9]\.[0-9]\.[0-9])?$/, loader: "file-loader" },
    ],
  },

  plugins: [
    new webpack.HotModuleReplacementPlugin(),
    new webpack.IgnorePlugin(new RegExp("^(fs|ipc)$")),
    new webpack.LoaderOptionsPlugin({
        options: {
            eslint: {
                failOnWarning: false,
                failOnError: true
            }
        }
    }),
    new webpack.DefinePlugin({
      'process.env.NODE_ENV': JSON.stringify(process.env.NODE_ENV || 'production'),
    }),
  ]
}