webpack.config.js

const path = require('path')

module.exports = {
  entry: './source/javascripts/application.js',
  output: {
    filename: 'bundle.js',
    path: path.resolve(__dirname, 'tmp/webpack-dist'),
  },
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: [
          { loader: 'style-loader' },
          { loader: 'css-loader' },
          {
            loader: 'postcss-loader',
            options: {
              plugins: function () {
                return [require('autoprefixer')]
              }
            }
          },
          { loader: 'sass-loader' },
        ]
      },
      {
        test: /\.css$/,
        use: [
          { loader: 'style-loader'},
          { loader: 'css-loader' },
          {
            loader: 'postcss-loader',
            options: {
              plugins: function () {
                return [require('autoprefixer')]
              }
            }
          }
        ]
      },
      {
        test: /\.(png|svg|jpg|gif)$/,
        use: ['file-loader']
      }
    ],
  },
}