rollup.config.js

import { terser } from 'rollup-plugin-terser';
import postcss from 'rollup-plugin-postcss'
import babel from 'rollup-plugin-babel';
import commonjs from 'rollup-plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import pkg from './package.json';
import resolve from 'rollup-plugin-node-resolve';
import svelte from 'rollup-plugin-svelte';

const production = !process.env.ROLLUP_WATCH;
const name = pkg.name
	.replace(/^(@\S+\/)?(svelte-)?(\S+)/, '$3')
	.replace(/^\w/, (m) => m.toUpperCase())
	.replace(/-\w/g, (m) => m[1].toUpperCase());

export default {
	input: !production ? 'src/main.js' : 'src/components/components.module.js',
	output: !production
		? {
				sourcemap: true,
				format: 'iife',
				name: 'app',
				file: 'public/bundle.js',
		  }
		: [
				{
					file: pkg.module,
					format: 'es',
					sourcemap: true,
					name,
				},
				{
					file: pkg.main,
					format: 'umd',
					sourcemap: true,
					name,
				},
		  ],
	plugins: [
		babel({
			runtimeHelpers: true,
		}),
    postcss({
      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');
			},

			/**
			 * Auto preprocess supported languages with
			 * '<template>'/'external src files' support
			 **/
      preprocess: [],
		}),

		// 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,
			dedupe: (importee) =>
				importee === 'svelte' || importee.startsWith('svelte/'),
		}),
		commonjs({
			include: ['node_modules/**'],
		}),

		// In dev mode, call `npm run start` once
		// the bundle has been generated
		!production && serve(),

		// 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,
	},
};

function serve() {
	let started = false;

	return {
		writeBundle() {
			if (!started) {
				started = true;

				require('child_process').spawn(
					'npm',
					['run', 'start', '--', '--dev'],
					{
						stdio: ['ignore', 'inherit', 'inherit'],
						shell: true,
					}
				);
			}
		},
	};
}