rollup.config.js

import svelte from 'rollup-plugin-svelte';
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';

const production = !process.env.ROLLUP_WATCH;

export default {
	input: 'src/index.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');
			},

			// this results in smaller CSS files
			cascade: false
		}),

		// 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
		// IMPORTANT !!! Buble or Babel should go AFTER Svelte plugin
		babel({
			babelrc: false,
			presets: [['@babel/preset-env', { modules: false }]],
		}),
		production && terser()
	]
};