Function onwarn

frameworks/lit/rollup.config.js:19–23

(warning)

    format: 'esm',
  },
  onwarn(warning) {
    if (warning.code !== 'THIS_IS_UNDEFINED') {
      console.error(`(!) ${warning.message}`);
    }
  },
  plugins: [
    replace({'Reflect.decorate': 'undefined'}),
    typescript(),