我怎么才能让我的React应用程序只在一个昂贵的计算完成时渲染？

import React, { Suspense } from 'react';

const ExpensiveComponent = React.lazy(() => import('./ExpensiveComponent'));

function App() {
  return (
    <div>
      <Suspense fallback={<div>Loading...</div>}>
        <ExpensiveComponent />
      </Suspense>
    </div>
  );
}

export default App;

import React, { Suspense } from 'react';
import { BrowserRouter as Router, Route, Switch } from 'react-router-dom';

const HomePage = React.lazy(() => import('./HomePage'));
const AboutPage = React.lazy(() => import('./AboutPage'));
const ContactPage = React.lazy(() => import('./ContactPage'));

function App() {
  return (
    <Router>
      <div>
        <Suspense fallback={<div>Loading...</div>}>
          <Switch>
            <Route exact path="/" component={HomePage} />
            <Route path="/about" component={AboutPage} />
            <Route path="/contact" component={ContactPage} />
          </Switch>
        </Suspense>
      </div>
    </Router>
  );
}

export default App;