sitemap.xml in next.js which is easy to extend with dynamic routes

sitemap.xml.tsx

// place in pages/sitemap.xml.tsx

const fs = require('fs')
import { endpoint } from '../config'

const Sitemap = () => null
Sitemap.getInitialProps = async ({ res }) => {
  if (!res) return {}
  const folder = 'pages'
  res.setHeader('content-type', 'application/xml')
  let content = fs
    .readdirSync(folder)
    .map(f => (f === '_app.tsx' ? '' : f))
    .filter(f => !f.startsWith(`_`))
    .filter(f => !f.startsWith(`[`))
    .filter(f => f !== `sitemap.xml.tsx`)
    .map(f => ({
      filename: f,
      updatedAt: fs
        .statSync(`${folder}/${f}`)
        .mtime.toISOString()
        .substr(0, 10)
    }))
    .map(f => ({ ...f, filename: f.filename.replace('.tsx', '') }))
    .map(f => ({ ...f, filename: `${endpoint}/${f.filename}` }))
    .map(f => `<url><loc>${f.filename}</loc><lastmod>${f.updatedAt}</lastmod></url>`)
    .join()

  res.end(`<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">${content}</urlset>`)
  return {}
}
export default Sitemap

Module not found: Can't resolve 'fs' in '/Users/dav/Desktop/dvld-nextjs/pages/sitemap'

'fs' module can only be used on server side.

how to generate sitemap from JSON data (data from database) like

Here: https://leerob.io/blog/nextjs-sitemap-robots