rollup.config.js

import babel from 'rollup-plugin-babel';
import commonjs from 'rollup-plugin-commonjs';
import livereload from 'rollup-plugin-livereload';
import resolve from 'rollup-plugin-node-resolve';
import svelte from 'rollup-plugin-svelte';
import { terser } from 'rollup-plugin-terser';
import postcss from 'rollup-plugin-postcss';
import replace from 'rollup-plugin-replace';
import autoPreprocess from 'svelte-preprocess';
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/index.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: [
    postcss({
      plugins: [],
    }),
    replace({
      'process.env.NODE_ENV': JSON.stringify(
        production ? 'production' : 'development'
      ),
    }),
    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('public/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: importee =>
        importee === 'svelte' || importee.startsWith('svelte/'),
    }),
    commonjs({
      include: ['node_modules/**'],
    }),

    // 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,
  },
};