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;
const name = pkg.name
  .replace(/^(@\S+\/)?(svelte-)?(\S+)/, '$3')
  .replace(/^\w/, (m) => m.toUpperCase())
  .replace(/-\w/g, (m) => m[1].toUpperCase());

export default {
  input: !production ? 'src/main.js' : 'src/components/components.module.js',
  output: !production
    ? {
        sourcemap: true,
        format: 'iife',
        name: 'app',
        file: 'public/bundle.js',
      }
    : [
        { file: 'dist/index.min.mjs', format: 'es' },
        { file: 'dist/index.min.js', format: 'umd', name },
      ],
  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
      customElement: true,
      css: (css) => {
        css.write('public/bundle.css');
      },
    }),

    // 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/rollup-plugin-commonjs
    resolve(),
    commonjs(),

    // 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,
  },
};