Webpack base config to publish libs to production with modern code

webpack.config.js

const path = require("path");
const webpack = require("webpack");
const UglifyJSPlugin = require("uglifyjs-webpack-plugin");

const PROD = process.env.NODE_ENV === "production";

const configureBabelLoader = browserlist => {
  return {
    test: /\.js$/,
    use: {
      loader: "babel-loader",
      options: {
        presets: [
          [
            "env",
            {
              debug: true,
              modules: false,
              useBuiltIns: true,
              targets: {
                browsers: browserlist
              }
            }
          ]
        ]
      }
    }
  };
};

const baseConfig = {
  output: {
    path: path.resolve(__dirname, "dist"),
    publicPath: "/",
    filename: "[name].js",
    library: "LibName",
    libraryTarget: "umd",
    libraryExport: "default",
    umdNamedDefine: true
  },
  plugins: PROD
    ? [
        new UglifyJSPlugin({
          sourceMap: true,
          uglifyOptions: {
            mangle: {
              // Works around a Safari 10 bug:
              // https://github.com/mishoo/UglifyJS2/issues/1753
              safari10: true
            }
          }
        })
      ]
    : []
};

const modernConfig = Object.assign({}, baseConfig, {
  entry: {
    'lib-name': path.resolve(__dirname, "src", "index.js")
  },
  module: {
    rules: [
      configureBabelLoader([
        // The last two versions of each browser, excluding versions
        // that don't support <script type="module">.
        "last 2 Chrome versions",
        "not Chrome < 60",
        "last 2 Safari versions",
        "not Safari < 10.1",
        "last 2 iOS versions",
        "not iOS < 10.3",
        "last 2 Firefox versions",
        "not Firefox < 54",
        "last 2 Edge versions",
        "not Edge < 15"
      ])
    ]
  }
});

const legacyConfig = Object.assign({}, baseConfig, {
  entry: {
    "lib-name-legacy": path.resolve(__dirname, "src", "index.js")
  },
  module: {
    rules: [configureBabelLoader(["> 1%", "last 2 versions", "Firefox ESR"])]
  }
});

module.exports = [modernConfig, legacyConfig];