php-flarum/js-packages/webpack-config/index.js

const fs = require('fs');
const path = require('path');
const webpack = require('webpack');

module.exports = function (options = {}) {
  return {
    // Set up entry points for each of the forum + admin apps, but only
    // if they exist.
    entry: (function () {
      const entries = {};

      for (const app of ['forum', 'admin']) {
        const file = path.resolve(process.cwd(), app + '.js');
        if (fs.existsSync(file)) {
          entries[app] = file;
        }
      }

      return entries;
    })(),

    module: {
      rules: [
        {
          test: /\.js$/,
          use: {
            loader: 'babel-loader',
            options: {
              presets: [
                [
                  '@babel/preset-env',
                  {
                    modules: false,
                    loose: true,
                  },
                ],
                ['@babel/preset-react'],
              ],
              plugins: [
                ['@babel/plugin-transform-runtime', { useESModules: true }],
                ['@babel/plugin-proposal-class-properties', { loose: true }],
                ['@babel/plugin-proposal-private-methods', { loose: true }],
                ['@babel/plugin-transform-react-jsx', { pragma: 'm' }],
              ],
            },
          },
        },
      ],
    },

    output: {
      path: path.resolve(process.cwd(), 'dist'),
      library: 'module.exports',
      libraryTarget: 'assign',
      devtoolNamespace: require(path.resolve(process.cwd(), 'package.json')).name,
    },

    externals: [
      {
        '@flarum/core/forum': 'flarum.core',
        '@flarum/core/admin': 'flarum.core',
        jquery: 'jQuery',
      },

      (function () {
        const externals = {};

        if (options.useExtensions) {
          for (const extension of options.useExtensions) {
            externals['@' + extension] = externals['@' + extension + '/forum'] = externals['@' + extension + '/admin'] =
              "flarum.extensions['" + extension + "']";
          }
        }

        return externals;
      })(),

      // Support importing old-style core modules.
      function (context, request, callback) {
        let matches;
        if ((matches = /^flarum\/(.+)$/.exec(request))) {
          return callback(null, "root flarum.core.compat['" + matches[1] + "']");
        }
        callback();
      },
    ],

    devtool: 'source-map',
  };
};