Generate sitemap XML for NextJs static sites based on exportPathMap

generate-sitemap.js

/*
Generates a sitemap based on the entries in exportPathMap in next.config.js file

Author: Joran Quinten

Don't forget to add the domain name as process variable PUBLIC_DOMAIN!

Trigger the file with a separate script in your package.json and add it to your build command in Netlify
(for instance, set Build command to: "npm run production && npm run postexport")

The postexport command runs the script post-export.js in my repo, which calls the generator:

// file contents "post-export.js":

    require('dotenv').config();
    const { generateSitemap } = require('./generate-sitemap');

    generateSitemap(process.env.PUBLIC_DOMAIN, './out/static/');

*/

const fs = require('fs');

// Read from the static map that's provided by next
const { exportPathMap } = require('./next.config');

// Format to the right date
const formatDate = date => `${date.toISOString().split('.')[0]}+0:00`;
// Priority is determined by path depth. Feel free to modify this if needed:
const getPriority = url => ((100 - (url.split('/').length - 2) * 10) / 100).toFixed(2);

// Just pick current date as last modified
const lastModified = formatDate(new Date());

// Set the header
const xmlHeader = `<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.sitemaps.org/schemas/sitemap/0.9 http://www.sitemaps.org/schemas/sitemap/0.9/sitemap.xsd">`;

// Wrap all pages in <urlset> tags
const xmlUrlWrapper = nodes => `${xmlHeader}
  ${nodes}
</urlset>`;

// Determine and return the nodes for every page
const xmlUrlNode = (domain, pageUrl, lastmod) => {
  const url = `${pageUrl}${pageUrl === '/' ? '' : '/'}`;
  const loc = `${domain}${url}`;
  const priority = getPriority(url);

  return `<url>
  <loc>${loc}</loc>
  <lastmod>${lastmod}</lastmod>
  <priority>${priority}</priority>
</url>`;
};

exports.generateSitemap = async (domain, targetFolder) => {
  if (!domain) {
    throw new Error('No domain provided!');
  }
  if (!targetFolder) {
    throw new Error('No targetFolder provided!');
  }
  const fileName = 'sitemap.xml';
  const writeLocation = `${
    targetFolder.endsWith('/') ? targetFolder : `${targetFolder}/`
  }${fileName}`;

  const entries = await exportPathMap();
  const pages = Object.entries(entries).map(item => item[0]);

  const sitemap = `${xmlUrlWrapper(
    pages.map(page => xmlUrlNode(domain, page, lastModified)).join(`
`)
  )}`;

  fs.writeFile(`${writeLocation}`, sitemap, err => {
    if (err) throw err;
    console.log(
      `sitemap.xml with ${pages.length} entries was written to ${targetFolder}${fileName}`
    );
  });
};