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 pkg from './package.json';

const production = !process.env.ROLLUP_WATCH;

export default [
  {
    input: 'src/dev/main.js',
    output: {
      sourcemap: true,
      format: 'iife',
      name: 'app',
      file: 'public/build/bundle.js',
    },
    plugins: [
      svelte({
        dev: !production,
        css: (css) => css.write('bundle.css'),
      }),
      resolve({
        browser: true,
        dedupe: (importee) =>
          importee === 'svelte' || importee.startsWith('svelte/'),
      }),
      commonjs(),
      !production && serve(),
      !production && livereload('public'),
      production && terser(),
    ],
    watch: { clearScreen: false },
  },
  {
    input: 'src/lib/ScrollShadow.svelte',
    output: { file: pkg.main, format: 'umd', name: 'ScrollShadow' },
    plugins: [svelte(), resolve(), commonjs()],
  },
  {
    input: 'src/lib/ScrollShadow.svelte',
    output: { file: pkg.module, format: 'es' },
    external: ['svelte/internal'],
    plugins: [svelte(), commonjs()],
  },
];

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,
        });
      }
    },
  };
}