rollup.config.js

import merge from 'deepmerge';
// use createSpaConfig for bundling a Single Page App
import { createSpaConfig } from '@open-wc/building-rollup';
// import { triggerAsyncId } from 'async_hooks';

// use createBasicConfig to do regular JS to JS bundling
// import { createBasicConfig } from '@open-wc/building-rollup';
import dynamicImportVars from '@rollup/plugin-dynamic-import-vars';

const baseConfig = createSpaConfig({
  // use the outputdir option to modify where files are output
  // outputDir: 'dist',

  // if you need to support older browsers, such as IE11, set the legacyBuild
  // option to generate an additional build just for this browser
  // legacyBuild: true,

  // development mode creates a non-minified build for debugging or development
  developmentMode: process.env.ROLLUP_WATCH === 'true',

  // set to true to inject the service worker registration into your index.html
  injectServiceWorker: false,
});

export default merge(baseConfig, {
  // if you use createSpaConfig, you can use your index.html as entrypoint,
  // any <script type="module"> inside will be bundled by rollup
  // input: './index.html',

  // alternatively, you can use your JS as entrypoint for rollup and
  // optionally set a HTML template manually
  input: 'index.html',
  output: {
    dir: './build/bundled',
    // file: './build/rollup/mist-app.js',
    sourcemap: true,
    format: 'esm',
  },
  plugins: [
    dynamicImportVars({
      // options
    }),
  ],
});