rollup.config.js

import svelte from 'rollup-plugin-svelte';
import commonjs from '@rollup/plugin-commonjs';
import resolve from '@rollup/plugin-node-resolve';
import livereload from 'rollup-plugin-livereload';
import { terser } from 'rollup-plugin-terser';
import { spawn } from 'child_process';
import css from 'rollup-plugin-css-only';
import { readFileSync, writeFileSync } from 'fs';

const production = !process.env.ROLLUP_WATCH;

function serve() {
  let server;

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

  return {
    writeBundle() {
      if (server) return;
      server = spawn('yarn', ['start', '-d'], {
        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: 'dist/build/bundle.js'
  },
  plugins: [
    svelte({
      compilerOptions: {
        // enable run-time checks when not in production
        dev: !production
      }
    }),
    css({
      // output: function (styles, styleNodes) {
      output: function (styles) {
        // make sure global_styles.css gets appended to bundle.css,
        // not prepended.
        // The ':global()' rules (https://svelte.dev/docs#style) get
        // prepended so we can't use them to overwrite bootstrap.css
        // rules
        let global_styles = readFileSync('src/global_style.css');
        styles += global_styles;
        writeFileSync('dist/build/bundle.css', styles);
      }
    }),

    // 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: ['svelte']
    }),
    commonjs(),

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

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

    // If we're building for production (npm run build
    // instead of npm run dev), minify
    production && terser()
  ],
  watch: {
    clearScreen: false
  }
};