gulp sitemap task

sitemap.config.js

// ISO_3166 language map. http://userpage.chemie.fu-berlin.de/diverse/doc/ISO_3166.html
var LANGUAGES = {
    en: 'en',
    ru: 'ru',
    sv: 'si',
    fi: 'fi',
    tr: 'tr',
    el: 'gr'
};

var URLS = {
    '/': {
        changefreq: 'daily',    // default weekly
        priority: 0.9,
    },
    '/about': {},
    '/affiliate': {},
    '/affiliate_terms': {},
    '/bitcoin': {},
    '/bonus': {},
    '/faq': {},

    '/gamelist': {},
    '/gamelist/1': {},          // hits
    '/gamelist/allgames': {},
    '/payment-methods': {},
    '/play-safe': {},
    '/promo': {
        priority: 0.9,
        changefreq: 'daily'
    },
    '/provability-fair-games': {},
    '/support': {},
    '/terms-and-conditions': {},
};

module.exports = {
    languages: LANGUAGES,
    urls: URLS,
};

sitemap.js

// Build sitemap for 7bit

// See https://support.google.com/webmasters/answer/2620865?hl=ru
'use strict';

var gulp = require('gulp'),
    plugins = require('gulp-load-plugins')({
        pattern: ['*'],
        lazy: false
    }),
    fs = require('fs'),
    _ = require('underscore'),
    builder = require('xmlbuilder');

var BASE = 'https://EXAMPLE.com',
    buildDir = plugins.path.resolve('./build'),
    SITEMAPXML = buildDir + '/sitemap.xml',
    config = require('../sitemap.config.js'),
    URLS = config.urls,          // sitemap urls
    LANGUAGES = config.languages; // ISO3166 languages map

gulp.task('sitemap', [], function() {

    try {fs.mkdirSync(buildDir);} catch (e) {}

    var xml = builder.create('urlset', { version: '1.0', encoding: 'UTF-8' })
            .att({
                'xmlns': 'http://www.sitemaps.org/schemas/sitemap/0.9',
                'xmlns:xhtml': 'http://www.w3.org/1999/xhtml'
            });

    xmlUrls(xml, URLS);

    // per language urls
    _.each(LANGUAGES, function(lang) {
        xmlUrls(xml, URLS, lang);
    });

    var sitemap = xml.end({ pretty: true, indent: '  ', newline: '\n' });

    fs.writeFileSync(SITEMAPXML, sitemap);
});

function xmlUrls(xml, urls, language) {
    _.each(urls, function(prop, url) {
        var languagePart = (language ? '/' + language : ''),
            fullUrl = BASE + languagePart + url,
            xUrl = xml.ele('url');

        xUrl.ele('loc', fullUrl);
        xUrl.ele('changefreq', prop.changefreq || 'weekly');

        if (prop.priority) {
            xUrl.ele('priority', prop.priority || 0.5);
        }

        _.each(LANGUAGES, function(ISO3166, nextLang) {
            if (nextLang !== language) {
                var langUrl = BASE + '/' + nextLang + url;
                xUrl.ele('xhtml:link')
                    .att({
                        rel: 'alternate',
                        hreflang: ISO3166,
                        href: langUrl,
                    });
            }
        });
    });
}

It produce:

<?xml version="1.0" encoding="UTF-8"?>
<urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9" xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <url>
    <loc>https://EXAMPLE.com/</loc>
    <changefreq>daily</changefreq>
    <priority>0.9</priority>
    <xhtml:link rel="alternate" hreflang="en" href="https://EXAMPLE.com/en/"/>
    <xhtml:link rel="alternate" hreflang="ru" href="https://EXAMPLE.com/ru/"/>
    <xhtml:link rel="alternate" hreflang="si" href="https://EXAMPLE.com/sv/"/>
    <xhtml:link rel="alternate" hreflang="fi" href="https://EXAMPLE.com/fi/"/>
    <xhtml:link rel="alternate" hreflang="tr" href="https://EXAMPLE.com/tr/"/>
    <xhtml:link rel="alternate" hreflang="gr" href="https://EXAMPLE.com/el/"/>
  </url>
<!-- ... -->
    <loc>https://EXAMPLE.com/gr/support</loc>
    <changefreq>weekly</changefreq>
    <xhtml:link rel="alternate" hreflang="en" href="https://EXAMPLE.com/en/support"/>
    <xhtml:link rel="alternate" hreflang="ru" href="https://EXAMPLE.com/ru/support"/>
    <xhtml:link rel="alternate" hreflang="si" href="https://EXAMPLE.com/sv/support"/>
    <xhtml:link rel="alternate" hreflang="fi" href="https://EXAMPLE.com/fi/support"/>
    <xhtml:link rel="alternate" hreflang="tr" href="https://EXAMPLE.com/tr/support"/>
    <xhtml:link rel="alternate" hreflang="gr" href="https://EXAMPLE.com/el/support"/>
  </url>
  <url>
    <loc>https://EXAMPLE.com/gr/terms-and-conditions</loc>
    <changefreq>weekly</changefreq>
    <xhtml:link rel="alternate" hreflang="en" href="https://EXAMPLE.com/en/terms-and-conditions"/>
    <xhtml:link rel="alternate" hreflang="ru" href="https://EXAMPLE.com/ru/terms-and-conditions"/>
    <xhtml:link rel="alternate" hreflang="si" href="https://EXAMPLE.com/sv/terms-and-conditions"/>
    <xhtml:link rel="alternate" hreflang="fi" href="https://EXAMPLE.com/fi/terms-and-conditions"/>
    <xhtml:link rel="alternate" hreflang="tr" href="https://EXAMPLE.com/tr/terms-and-conditions"/>
    <xhtml:link rel="alternate" hreflang="gr" href="https://EXAMPLE.com/el/terms-and-conditions"/>
  </url>
</urlset>