rollup.config.js

import { terser } from 'rollup-plugin-terser'
import autoPreprocess from 'svelte-preprocess'
import babel from 'rollup-plugin-babel'
import commonjs from 'rollup-plugin-commonjs'
import livereload from 'rollup-plugin-livereload'
import pkg from './package.json'
import resolve from 'rollup-plugin-node-resolve'
import svelte from 'rollup-plugin-svelte'

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: pkg.module,
          format: 'es',
          sourcemap: true,
          name
        },
        {
          file: pkg.main,
          format: 'umd',
          sourcemap: true,
          name
        }
      ],
  plugins: [
    babel({
      runtimeHelpers: true
    }),
    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('bundle.css')
      },

      /**
       * Auto preprocess supported languages with
       * '<template>'/'external src files' support
       **/
      preprocess: autoPreprocess({
        postcss: true,
        scss: { includePaths: ['src', 'node_modules'] }
      })
    }),

    // 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({
      browser: true,
      dedupe: ['svelte']
    }),
    commonjs({
      include: ['node_modules/**']
    }),

    // 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

        require('child_process').spawn(
          'npm',
          ['run', 'start', '--', '--dev'],
          {
            stdio: ['ignore', 'inherit', 'inherit'],
            shell: true
          }
        )
      }
    }
  }
}