react-server-error-boundary.js

import express from 'express';
import React from 'react';
import { renderToString } from 'react-dom/server';

const app = express();

class ErrorBoundary extends React.Component {
  constructor(props) {
    super(props);
    this.state = { hasError: false };
  }

  componentDidCatch(error, info) {
    // Display fallback UI
    console.log("componentDidCatch");
    this.setState({ hasError: true });
  }

  render() {
    if (this.state.hasError) {
      // You can render any custom fallback UI
      return <h1>Something went wrong.</h1>;
    }
    return this.props.children;
  }
}

class ThrowingComponent extends React.Component {
  render() {
    throw new Error("Ooooops");
  }
}

app.get('/', (req, res) => {
  const appString = renderToString(
    (
      <ErrorBoundary>
        <ThrowingComponent />
      </ErrorBoundary>
    )
  );
  res.send(appString);
});

const port = 3001;
app.listen(port);
console.log(`Listening on port ${port}`);