react.server.js

// Original demo.
async function renderReactTree(res, props) {
  await waitForWebpack();
  const manifest = readFileSync(
    path.resolve(__dirname, '../build/react-client-manifest.json'),
    'utf8'
  );
  const moduleMap = JSON.parse(manifest);
  pipeToNodeWritable(React.createElement(ReactApp, props), res, moduleMap);
}

// Generalized version.
async function renderReactTree(res, component, props) {
  await waitForWebpack();
  const manifest = readFileSync(
    path.resolve(__dirname, '../build/react-client-manifest.json'),
    'utf8'
  );
  const moduleMap = JSON.parse(manifest);
  pipeToNodeWritable(React.createElement(component, props), res, moduleMap);
}