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";
import json from "rollup-plugin-json";
import copy from "rollup-plugin-copy";

const production = !process.env.ROLLUP_WATCH;

export default {
	input: "src/main.js",
	output: {
		sourcemap: true,
		format: "iife",
		name: "app",
		file: "public/build/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/build/bundle.css");
			}
		}),
		json({
			// All JSON files will be parsed by default,
			// but you can also specifically include/exclude files
			include: "node_modules/**",
			exclude: ["node_modules/foo/**", "node_modules/bar/**"],

			// for tree-shaking, properties will be declared as
			// variables, using either `var` or `const`
			preferConst: true, // Default: false

			// specify indentation for the generated default export —
			// defaults to '\t'
			indent: "  ",

			// ignores indent and generates the smallest code
			compact: true, // Default: false

			// generate a named export for every property of the JSON object
			namedExports: true // Default: true
		}),
		copy({
			targets: [
				{
					src: "node_modules/bootstrap/dist/**/*",
					dest: "public/vendor/bootstrap"
				},
				{
					src: "node_modules/jquery/dist/jquery.min.js",
					dest: "public/vendor/jquery"
				}
			]
		}),

		// 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/plugins/tree/master/packages/commonjs
		resolve({
			browser: true,
			dedupe: importee =>
				importee === "svelte" || importee.startsWith("svelte/")
		}),
		commonjs(),

		// 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
					}
				);
			}
		}
	};
}