server.js

// server.js
const { createServer } = require('http');
const { parse } = require('url');
const next = require('next');

const dev = process.env.NODE_ENV !== 'production';
const app = next({ dev });
const handle = app.getRequestHandler();

app.prepare().then(() => {
  createServer((req, res) => {
    // Be sure to pass `true` as the second argument to `url.parse`.
    // This tells it to parse the query portion of the URL.
    const parsedUrl = parse(req.url, true);
    const { pathname, query } = parsedUrl;

    if (pathname === '/a') {
      app.render(req, res, '/a', query);
    } else if (pathname === '/b') {
      app.render(req, res, '/b', query);
    } else {
      handle(req, res, parsedUrl);
    }
  }).listen(3005, (err) => {
    if (err) throw err;
    console.log('> Ready on http://localhost:3005');
  });
});