webpack remove unused code options

webpack-terser.js

const optimizationOptions = {
  mode: PRODUCTION ? `production` : `development`,
  module: {rules},
  optimization: {
    chunkIds: `named`,
    moduleIds: PRODUCTION ? `hashed` : `named`,
    usedExports: true,
    minimize: PRODUCTION,
    minimizer: [
      new TerserPlugin({
        extractComments: false,
        parallel: true,
        terserOptions: {
          // see options descriptions at https://github.com/terser/terser#compress-options
          // full options list https://github.com/terser/terser/blob/master/lib/compress/index.js
          compress: {
            defaults: false, // explicitly enabling safe compress options
            unused: true, // drop unreferenced functions, variables and exports marked by webpack
            dead_code: true, // remove unreachable code
            properties: true, // foo["bar"] -> foo.bar
            computed_props: true, // {["computed"]: 1} -> {computed: 1}
            evaluate: true, // evaluate constant expressions 1 + 1 => 2
          },
          mangle: {
            keep_classnames: true, // preserve classnames to ensure this.constructor.name references work as expected, used in NamedError class
          },
          output: {
            comments: false,
            semicolons: false, // use newlines when possible, so devtools don't hang
          },
        },
      }),
    ],
  },
};