server.js

/**
 * Based on https://zenn.dev/sotszk/articles/b4e6a4e19d2e35
 */

const express = require('express');
const next = require('next');
const https = require('https');
const fs = require('fs');

const port = parseInt(process.env.PORT || '443');
const host = '0.0.0.0';

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

(async () => {
  await app.prepare();
  const expressApp = express();

  expressApp.get('*', (req, res) => handle(req, res));

  // Use HTTPS if HTTPS option enabled
  const hasCertificates =
    fs.existsSync('./certificates/localhost.key') &&
    fs.existsSync('./certificates/localhost.crt');
  const useHttps =
    process.env.HTTPS === 'true' &&
    hasCertificates;

  if (useHttps) {
    const options = {
      key: fs.readFileSync('./certificates/localhost.key'),
      cert: fs.readFileSync('./certificates/localhost.crt'),
    };
    const server = https.createServer(options, expressApp);
    server.listen(port, host);
    console.log(`> Ready on https://localhost:${port}`);
  } else {
    expressApp.listen(port, host);
    console.log(`> Ready on http://localhost:${port}`);
  }
})();