rollup.config.js

import svelte from "rollup-plugin-svelte";
import resolve from "rollup-plugin-node-resolve";
import commonjs from "rollup-plugin-commonjs";
import { terser } from "rollup-plugin-terser";
import copy from "rollup-plugin-copy";

const production = !process.env.ROLLUP_WATCH;

export default {
  input: "src/main.js",
  output: {
    sourcemap: true,
    format: "iife",
    name: "app",
    file: "public/bundle.js"
  },
  plugins: [
    svelte({
      // opt in to v3 behaviour today
      skipIntroByDefault: true,
      nestedTransitions: true,

      // 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");
      }
    }),

    // 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(),

    // If we're building for production (npm run build
    // instead of npm run dev), minify
    production && terser(),
    production && copy({ "public/index.html": "public/200.html" })
  ]
};