Dynamic Sitemap creation for NextJS based projects

server.js

const express = require('express');
const next = require('next');
const sm = require('sitemap');
const axios = require('axios');

const port = parseInt(process.env.PORT, 10) || 3000;
const dev = process.env.NODE_ENV !== 'production';
const app = next({ dev });
const handle = app.getRequestHandler();

const determinePriority = (url) => {
  if (url.includes('buy/')) {
    return 0.6
  } else if (url.includes('blog/')) {
    return 0.8
  } else {
    return 1.0
  }
};

const createSitemap = (res) => {
  let urlRoutes = [];
  
  let sitemap = sm.createSitemap ({
    hostname: 'base url of site',
    cacheTime: 60
  });
  
  axios.get('rest endpoint of dynamic page slugs')
    .then(function(response) {
      urlRoutes = [...urlRoutes, ...response.data]
      urlRoutes.map((item) => {
        sitemap.add({
          url: item,
          changefreq: 'daily',
          priority: determinePriority(item)
        })
      })
      res.send( sitemap.toString() )
    });
};

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

    server.get('/sitemap.xml', function(req, res) {
      res.header('Content-Type', 'application/xml');
      createSitemap(res);
    });

    server.get('/:slug', (req, res) => {
      const actualPage = '/page'
      const queryParams = { slug: req.params.slug }
      return app.render(req, res, actualPage, queryParams)
    });

    server.get('/', (req, res) => {
      const actualPage = '/page'
      const queryParams = { slug: 'homepage', modal: req.params.modal }
      return app.render(req, res, actualPage, queryParams)
    });

    server.get('*', (req, res) => {
      const pathname = req.originalUrl.substr(1);
      return handle(req, res)
    });

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