rollup.config.js

import css from 'rollup-plugin-css-only';
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';
import babel from 'rollup-plugin-babel';
import { terser } from 'rollup-plugin-terser';

export default {
  input: 'client/index.js',  
  output: {
    sourcemap: false,  
    format: 'iife',
    name: 'app',
    file: 'public/bundle.js'
  },
  plugins: [
    css({ output: 'public/bundle.css' }),

    // If you have external dependencies installed from
    // npm, you'll most likely need these plugins. In
    // some cases you'll need additional configuration —
    // consult the documentation for details:
    // https://github.com/rollup/rollup-plugin-commonjs
    resolve(),
    commonjs(),

    // If we're building for production (npm run build
    // instead of npm run dev), transpile and minify
    babel({
      runtimeHelpers: true,
      exclude: 'node_modules/**',
    }),
    terser()
  ]
};