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 css from 'rollup-plugin-css-only';
import preprocess from 'svelte-preprocess';
import { svelteSVG } from 'rollup-plugin-svelte-svg';

import config from './svelte.config.mjs';

const production = !process.env.ROLLUP_WATCH;

function serve() {
  let server;

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

  return {
    writeBundle() {
      if (server) return;
      server = require('child_process').spawn('npm', ['run', 'start', '--', '--dev'], {
        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: 'public/build/bundle.js'
  },
  plugins: [
    svelte({
      preprocess: preprocess({
        ...config.preprocessOptions,
        sourceMap: !production,
      }),
      compilerOptions: {
        dev: !production
      },
      onwarn: (warning, handler) => {
        const { code, } = warning;
        return code === 'css-unused-selector' ? undefined : handler(warning);
      },
    }),
    css({
      output: 'bundle.css'
    }),
    svelteSVG({
      svgo: {}
    }),
    resolve({
      browser: true,
      dedupe: ['svelte']
    }),
    commonjs(),
    !production && serve(),
    !production && livereload('public'),
    production && terser()
  ],
  watch: {
    clearScreen: false
  }
};