create-react-app-express/src/handle-universal-render.js

Express server for your Create React App, ready for SSR

const React = require('react');
const { renderToNodeStream } = require('react-dom/server');

function handleUniversalRender(reactElement) {
  return (req, res) => renderToNodeStream(reactElement);
}

module.exports = handleUniversalRender;