How to generate a sitemap.xml with Node.js the simple way

XML

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
    <url>
        <loc>https://maxschmitt.me/</loc>
        <lastmod>2020-06-01</lastmod>
        <changefreq>daily</changefreq>
        <priority>1</priority>
    </url>
    <url>
        <loc>https://maxschmitt.me/posts</loc>
        <lastmod>2020-06-01</lastmod>
        <changefreq>daily</changefreq>
        <priority>1</priority>
    </url>
    <url>
        <loc>https://maxschmitt.me/posts/github-actions-ssh-key</loc>
        <lastmod>2020-05-17</lastmod>
        <changefreq>monthly</changefreq>
        <priority>0.5</priority>
    </url>
    <url>
        <loc>https://maxschmitt.me/posts/error-reporting-rollbar-nextjs</loc>
        <lastmod>2020-01-10</lastmod>
        <changefreq>monthly</changefreq>
        <priority>0.5</priority>
    </url>
    <!-- ... -->
</urlset>

JS

const fs = require('fs-extra')
const xml = require('xml')

class SitemapWriter {
	constructor({ outFile, host }) {
		this.outFile = outFile
	}

	async writeSitemap(pages) {
		// Construct the XML object
		const xmlObject = {
			urlset: [
				// <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
				{
					_attr: {
						xmlns: 'http://www.sitemaps.org/schemas/sitemap/0.9',
					},
				},

				// For every page of the site, generate a <url> object
				...pages.map((page) => {
					return {
						// <url>
						url: [
							// <loc>http://www.example.com/</loc>
							{ loc: page.href },

							// <lastmod>2005-01-01</lastmod>
							{ lastmod: page.srcFileLastModifiedAt },

							// <changefreq>monthly</changefreq>
							{ changefreq: 'monthly' },

							// <priority>0.8</priority>
							{ priority: 0.5 },
						],
					}
				}),
			],
		}

		// Generate the XML markup
		const xmlString = xml(xmlObject)

		// Write the file to disk
		await fs.writeFile(this.outFile, '<?xml version="1.0" encoding="UTF-8"?>' + xmlString)
	}
}