server.js

const { join } = require('path');
const express = require('express');
const next = require('next');
const cache = require('lru-cache'); // for using least-recently-used based caching
const csp = require('./csp');

const PORT = 8000;
const dev = process.env.NODE_ENV !== 'production';
const app = next({ dev });
const handle = app.getRequestHandler();

const ssrCache = new cache({
  max: 20, // not more than 20 results will be cached
  maxAge: 1000 * 60 * 5 // 5 mins
});

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

  csp(server);

  server.get('/', (req, res) => {
    renderAndCache(req, res, '/');
  });

  server.get('*', (req, res) => {
    if (req.url.includes('/sw')) {
      const filePath = join(__dirname, 'static', 'workbox', 'sw.js');
      app.serveStatic(req, res, filePath);
    } else if (req.url.startsWith('static/workbox/')) {
      app.serveStatic(req, res, join(__dirname, req.url));
    } else {
      handle(req, res, req.url);
    }
  });

  server.listen(PORT, err => {
    if (err) throw err;
    console.log(`> Live @ http://localhost:${PORT}`);
  });

  async function renderAndCache(req, res, pagePath, queryParams) {
    const key = req.url;

    // if page is in cache, server from cache
    if (ssrCache.has(key)) {
      res.setHeader('x-cache', 'HIT');
      res.send(ssrCache.get(key));
      return;
    }

    try {
      // if not in cache, render the page into HTML
      const html = await app.renderToHTML(req, res, pagePath, queryParams);

      // if something wrong with the request, let's skip the cache
      if (res.statusCode !== 200) {
        res.send(html);
        return;
      }

      ssrCache.set(key, html);

      res.setHeader('x-cache', 'MISS');
      res.send(html);
    } catch (err) {
      app.renderError(err, req, res, pagePath, queryParams);
    }
  }
});