Basic Webpack 4 starter. This will build images, sass & js.

webpack.config.js

const MiniCssExtractPlugin = require('mini-css-extract-plugin')
const CleanWebpackPlugin = require('clean-webpack-plugin')
const autoprefixer = require('autoprefixer')
const path = require('path')

module.exports = {
  // Set entry & output paths
  entry: './src/index.js',
  output: {
    path: path.resolve(__dirname, 'assets'),
    filename: 'app.min.js'
  },
  module: {
    rules: [
      // ES6 Javascript
      {
        test: /\.js$/,
        exclude: /node_modules/,
        use: {
          loader: 'babel-loader'
        }
      },
      // Images
      {
        test: /\.(jpg|png|gif|svg)$/,
        use: {
          loader: 'file-loader',
          options: {
            name: '[path][name].[ext]',
            // outputPath: './media/',
            context: './src'
          }
        }
      },
      // CSS & SASS
      {
        test: /\.s?css$/,
        use: [
          MiniCssExtractPlugin.loader,
          {
            loader: 'css-loader',
            options: {
              minimize: {
                safe: true
              }
            }
          },
          {
            loader: 'postcss-loader',
            options: {
              autoprefixer: {
                browsers: ['last 2 versions']
              },
              plugins: () => [
                autoprefixer
              ]
            }
          },
          {
            loader: 'sass-loader',
            options: {}
          }
        ]
      }
    ]
  },
  plugins: [
    // Extract the CSS from the webpack bundle and put into a seperate file
    new MiniCssExtractPlugin({
      filename: 'css/app.css',
      chunkFilename: '[id].css'
    }),
    // Wipe the assets folder each time
    new CleanWebpackPlugin('assets')
  ]
}