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 sveltePreprocess from 'svelte-preprocess';
import childProcess from 'child_process';

const production = !process.env.ROLLUP_WATCH;

export default {
  input: 'client/main.js',
  output: {
    sourcemap: !production,
    format: 'iife',
    name: 'app',
    file: 'public/assets/js/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/assets/css/bundle.css');
      },

      // set preprocess
      preprocess: sveltePreprocess()
    }),

    // 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;


        childProcess.spawn(
          'npm', ['run', 'dev:server-only'],
          {
            stdio: ['ignore', 'inherit', 'inherit'],
            shell: true
          }
        );
      }
    }
  };
}