const ExtractTextPlugin = require('extract-text-webpack-plugin');
const path = require('path');

module.exports = {
  entry: ['./src/js/index.js'],
  output: {
    filename: 'app.bundle.js',
    path: path.resolve(__dirname, 'src/assets'),
    publicPath: '/assets/',
  },
  devtool: 'source-map',
  module: {
    rules: [{
      test: /.scss$/,
      use: ExtractTextPlugin.extract({
        fallback: 'style-loader',
        use: ['css-loader', 'sass-loader'],
        publicPath: '/assets/',
      }),
    }],
  },
  devServer: {
    contentBase: path.resolve(__dirname, 'src'),
    compress: false,
    publicPath: 'http://localhost:8080/assets/',
    // port: 8080,
    watchContentBase: true,
    public: 'app.dev',
    proxy: {
      '/api': {
        target: 'http://app.dev',
        secure: false,
      },
    },
  },
  plugins: [
    new ExtractTextPlugin({
      filename: 'app.css',
      disable: false,
      allChunks: true,
    }),
  ],
};

"scripts": {
        "dev": "webpack-dev-server --hot --inline --open",
        "prod": "webpack -p"
    }

yarn run v0.19.1
$ webpack-dev-server --open
Project is running at http://app.dev/
webpack output is served from http://localhost:8080/assets/
Content not from webpack is served from /Users/hendrik/Documents/Github/Projects/app/src....