rollup.config.js

import svelte from "rollup-plugin-svelte";
import resolve from "@rollup/plugin-node-resolve";
import commonjs from "@rollup/plugin-commonjs";
import replace from '@rollup/plugin-replace';
import { terser } from "rollup-plugin-terser";
import css from 'rollup-plugin-css-only';

const production = !process.env.ROLLUP_WATCH;
const mode = production ? 'production' : 'development';

export default {
  input: "src/main.js",
  output: {
    sourcemap: true,
    format: "iife",
    name: "app",
    file: "public/bundle.js",
  },
  plugins: [
    replace({
      // Replace it for immer.js esm (see https://github.com/immerjs/immer/issues/557)
      'process.env.NODE_ENV': JSON.stringify(mode),
    }),
		svelte({
			compilerOptions: {
				// 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({ output: '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), minify
    production && terser(),
  ],
};