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;
  });
};