webpack.prod.js

const merge = require('webpack-merge');
const UglifyJSPlugin = require('uglifyjs-webpack-plugin');
const common = require('./webpack.common.js');
const ExtractTextPlugin = require("extract-text-webpack-plugin");
const extractSass = new ExtractTextPlugin({
  filename: "../css/main.css"
});

module.exports = merge(common, {
  module: {
    rules: [
      {
        test: /\.scss$/,
        use: extractSass.extract({
          use: [
            {
              loader: "css-loader",
              options: {
                minimize: true
              }
            },
            {
              loader: "postcss-loader"
            },
            {
              loader: "sass-loader"
            }
          ],
        })
      },
    ]
  },
  plugins: [
    extractSass,
    new UglifyJSPlugin()
  ]
});