The identifier for the entry points when the application uses Self-controlled Routing.

App.[tj]sx is not the actual entry. Modern.js will generate the real entry for application. The content is roughly as follows:

import React from 'react';
import ReactDOM from 'react-dom/client';
import { createApp, bootstrap } from '@modern-js/runtime';
// App.[jt]sx
import App from '@_modern_js_src/App';
// runtime plugin
import { router } from '@modern-js/runtime/plugins';

const IS_BROWSER = typeof window !== 'undefined' && !== 'nodejs';
const MOUNT_ID = 'root';

let AppWrapper = null;

function render() {
  AppWrapper = createApp({
    plugins: [
     router({...{"serverBase":["/"]}, ...App.config?.router}),
  if (IS_BROWSER) {
    bootstrap(AppWrapper, MOUNT_ID, null, ReactDOM);
  return AppWrapper

AppWrapper = render();
export default AppWrapper;

In the multi-entry scenario, each entry can have its own App.[jt]sx. See Entries for details.