rollup.config.js

import svelte from 'rollup-plugin-svelte-hot';
import sveltePreprocess from 'svelte-preprocess';
import resolve from '@rollup/plugin-node-resolve';
import commonjs from '@rollup/plugin-commonjs';
import svg from 'rollup-plugin-svg';
import json from '@rollup/plugin-json';
import dsv from '@rollup/plugin-dsv';
import hmr from 'rollup-plugin-hot';
import execute from 'rollup-plugin-execute';
import { terser } from 'rollup-plugin-terser';

const isWatch = !!process.env.ROLLUP_WATCH;
const isLiveReload = !!process.env.LIVERELOAD;
const isDev = isWatch || isLiveReload;
const isProduction = !isDev;
const isHot = isWatch && !isLiveReload;

const preprocess = sveltePreprocess({
	postcss : {
		plugins : [ require('autoprefixer') ]
	}
});

function serve() {
	let server;

	function toExit() {
		if (server) server.kill(0);
	}

	return {
		name        : 'svelte/template:serve',
		writeBundle() {
			if (server) return;
			server = require('child_process').spawn('npm', [ 'run', 'start', '--', '--dev' ], {
				stdio : [ 'ignore', 'inherit', 'inherit' ],
				shell : true
			});

			process.on('SIGTERM', toExit);
			process.on('exit', toExit);
		}
	};
}

export default {
	input   : 'src/main.js',
	output  : {
		sourcemap : true,
		format    : 'iife',
		name      : 'app',
		file      : 'public/build/bundle.js'
	},
	plugins : [
		svelte({
			dev        : !isProduction,
			hydratable : isProduction,
			css        : (css) => {
				css.write('bundle.css');
			},
			hot        : isHot && {
				optimistic : true
			},
			preprocess
		}),
		resolve({
			browser : true,
			dedupe  : [ 'svelte' ]
		}),
		commonjs(),
		json(),
		dsv(),
		svg(),
		// In dev mode, call `npm run start` once
		// the bundle has been generated
		isDev && serve(),

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

		// If we're building for production (npm run build
		// instead of npm run dev), minify
		isProduction && terser(),

		isDev &&
			hmr({
				public          : 'public',
				inMemory        : true,
				compatModuleHot : !isHot
			}),

		isDev && execute('node scripts/copy-template.js')
	],
	watch   : {
		clearScreen : false
	}
};