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";

const production = !process.env.ROLLUP_WATCH;

export default {
  input: "src/main.js",
  output: {
    sourcemap: !production,
    format: "iife",
    name: "app",
    file: "public/bundle.js"
  },
  plugins: [
    svelte({
      dev: !production,
      // Tell the compiler to output a custom element.
      customElement: true
    }),
    // 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(),

    // Enable live reloading in development mode
    !production && livereload("public"),

    // Minify the production build (npm run build)
    production && terser()
  ]
};