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Working with Express.js

If using express, hot server hot module reloading may not work after these steps

Express has its own route stack, so reloading require cache will not be enough to reload the routes inside express.

Add global callback in express

For hot module reloading with Express and Next.js, setting up a global callback to clear the Express route cache is required. This allows route updates to be recognized without server restarts.

server/express.js
import express from 'express';
import next from 'next';

const dev = process.env.NODE_ENV !== 'production';
const hostname = 'localhost';
const port = 3000;
const app = next({ dev, hostname, port });
const handle = app.getRequestHandler();

global.clearRoutes = () => {
  server._router.stack = server._router.stack.filter((k) => !(k && k.route && k.route.path));
};

app.prepare().then(() => {
  const server = express();

  server.all('*', (req, res) => {
    const parsedUrl = new URL(req.url, `http://${req.headers.host}`);
    const { pathname, query } = parsedUrl;

    handle(req, res, parsedUrl);
  });

  server.listen(port, () => {
    console.log(`> Ready on http://${hostname}:${port}`);
  });
});

Trigger callback in revalidation

add a global callback in _document.js to clear the Express route cache during revalidation, allowing updated routes to be served without server restarts.

pages/_document.js
class MyDocument extends Document {
  static async getInitialProps(ctx) {
    if (ctx?.pathname && !ctx?.pathname?.endsWith('_error')) {
      await revalidate().then((shouldUpdate) => {
        if (shouldUpdate) {
          global.clearRoutes();
        }
      });
    }

    const initialProps = await Document.getInitialProps(ctx);
    return initialProps;
  }

  render() {
    return (
      <Html>
        <Head />
        <body>
          <Main />
          <NextScript />
        </body>
      </Html>
    );
  }
}