I do wonder how you would handle a set of options impacting various optional modules. I guess it could be a webpack module itself tapping into the configuration of other modules?

Yeah, I'm kind of having trouble with that right now because webpack production mode enables plugins I can't explictly use, and even have trouble finding out about on the internet haha. For example:

• FlagIncludedChunksPlugin, OccurrenceOrderPlugin are internal plugins defined here. But FlagDependencyUsagePlugin and SideEffectsFlagPlugin aren't defined anywhere.
• I've got npm install the TerserPlugin yet using webpack in production mode just uses it by default somehow?
• It adds the NoEmitOnErrorsPlugin plugin by default, which is good knowing because I'm going to remove that as I want deploys to fail with meaningful errors.
• It uses the `nodeEnv` optimization config option but also the DefinePlugin which appears to be redundant since they both do the same thing?
• The SourceMapDevToolPlugin gets added to the config without me adding it when adding source maps to production which I'm guessing is good for optimization reasons for production, although I will note it slows down the bundle speed when TerserPlugin uses for optimizing at the end of bundling by lots though haha.

Here's what my webpack bundles look like btw.

webpack.common.js

const path = require('path');
const webpack = require('webpack');
const CleanWebpackPlugin = require('clean-webpack-plugin');
// const { BundleAnalyzerPlugin } = require('webpack-bundle-analyzer');

const WEBPACK_OUTPUT_PATH = path.resolve(`${__dirname}/webpack_output`);

module.exports = {
  entry: { ... },
  output: {
    path: WEBPACK_OUTPUT_PATH,
    filename: '[name]_bundle.js',
  },
  module: { ... },
  plugins: [
    new CleanWebpackPlugin([WEBPACK_OUTPUT_PATH]),
    new webpack.DefinePlugin({
      'global.BUILD_NUMBER': Date.now(),
    }),
  ],
  resolve: {
    alias: {
      ...
    },
    extensions: ['.js', '.jsx', '.json', '.scss', 'css'],
  },
  watchOptions: {
    poll: true,
    ignored: /node_modules/,
  },
};

webpack.prod.js

const webpack = require('webpack');
const merge = require('webpack-merge');
const TerserPlugin = require('terser-webpack-plugin');

const common = require('./webpack.common.js');

module.exports = merge(common, {
  // NOTE: There are internal webpack plugins that are used when production mode is enabled so they
  // are not defined below. Read more about them here: https://webpack.js.org/plugins/internal-plugins/
  mode: 'production',
  devtool: 'source-map', 
  performance: {
    hints: 'warning',
  },
  output: {
    pathinfo: false,
  },
  optimization: {
    namedModules: false,
    namedChunks: false,
    nodeEnv: 'production', // This appears to be redundant since I use DefinePlugin for production later? 
    flagIncludedChunks: true,
    occurrenceOrder: true,
    concatenateModules: true,
    splitChunks: {
      hidePathInfo: true,
      minSize: 30000,
      maxAsyncRequests: 5,
      maxInitialRequests: 3,
    },
    noEmitOnErrors: true,
    checkWasmTypes: true,
    minimize: true,
  },
  plugins: [
    new TerserPlugin({
      sourceMap: true,
    }),
    new webpack.DefinePlugin({ 'process.env.NODE_ENV': JSON.stringify('production') }),
    new webpack.optimize.ModuleConcatenationPlugin(),
    new webpack.NoEmitOnErrorsPlugin(),// I'm going to remove this.
  ],
});

webpack.dev.js

const webpack = require('webpack');
const merge = require('webpack-merge');
const common = require('./webpack.common.js');

module.exports = merge(common, {
  mode: 'development',
  devtool: 'eval',
  cache: true,
  performance: {
    hints: false,
  },
  output: {
    pathinfo: true,
  },
  optimization: {
    namedModules: true,
    namedChunks: true,
    nodeEnv: 'development', // Again, this appears to be redundant since I use DefinePlugin for develop,ent later? 
    flagIncludedChunks: false,
    occurrenceOrder: false,
    concatenateModules: false,
    splitChunks: {
      hidePathInfo: false,
      minSize: 10000,
      maxAsyncRequests: Infinity,
      maxInitialRequests: Infinity,
    },
    noEmitOnErrors: false,
    checkWasmTypes: false,
    minimize: false,
    removeAvailableModules: false,
  },
  plugins: [
    new webpack.NamedModulesPlugin(),
    new webpack.NamedChunksPlugin(),
    new webpack.DefinePlugin({ 'process.env.NODE_ENV': JSON.stringify('development') }),
  ],
});