web-dev-server.config.mjs

// import { hmrPlugin, presets } from '@open-wc/dev-server-hmr';
import { fromRollup } from '@web/dev-server-rollup';
import rollupCommonjs from '@rollup/plugin-commonjs';
import rollupReplace from '@rollup/plugin-replace';

const commonjs = fromRollup(rollupCommonjs);
const replace = fromRollup(rollupReplace);


/** Use Hot Module replacement by adding --hmr to the start command */
const hmr = process.argv.includes('--hmr');

export default /** @type {import('@web/dev-server').DevServerConfig} */ ({
  open: '/',
  watch: !hmr,
  /** Resolve bare module imports */
  nodeResolve: {
    exportConditions: ['browser', 'development'],
  },
  
  /** Compile JS for older browsers. Requires @web/dev-server-esbuild plugin */
  // esbuildTarget: 'auto'

  /** Set appIndex to enable SPA routing */
  appIndex: './index.html',

  plugins: [
    /** Use Hot Module Replacement by uncommenting. Requires @open-wc/dev-server-hmr plugin */
    // hmr && hmrPlugin({ exclude: ['**/*/node_modules/**/*'], presets: [presets.litElement] }),
    commonjs({
      include: [
        // the commonjs plugin is slow, list the required packages explicitly:
        '**/node_modules/color-scales/**/*',
      ],
    }),
    replace({
      'process.env.NODE_ENV': JSON.stringify('dev'),
      preventAssignment: true,
    }),
  ],

  // See documentation for all available options
});