rollup.config.js

import svelte from 'rollup-plugin-svelte';
import resolve from 'rollup-plugin-node-resolve';
import commonjs from 'rollup-plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';

const production = !process.env.ROLLUP_WATCH;

let config;

if (!production) {
  config = {
    input: 'src/examples/simple/main.js',
    output: {
      sourcemap: true,
      format: 'iife',
      name: 'app',
      file: 'public/bundle.js',
    },
    plugins: [
      svelte({
        // enable run-time checks when not in production
        dev: !production,
        // we'll extract any component CSS out into
        // a separate file — better for performance
        css: css => {
          css.write('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({ browser: true }),
      commonjs(),

      // Watch the `public` directory and refresh the
      // browser on changes when not in production
      !production && livereload('public'),

      // If we're building for production (npm run build
      // instead of npm run dev), minify
      production && terser(),
    ],
    watch: {
      clearScreen: false,
    },
  };
} else {
  config = {
    input: 'src/index.js',
    output: [
      {
        file: 'dist/es/index.mjs',
        format: 'es',
      },
      {
        file: 'dist/cjs/index.js',
        format: 'cjs',
      },
    ],
  };
}

export default config;