Create an xml and open it from the client-side

Today I've been wondering if it was possible to create an xml file from the client-side using JavaScript.

Let's suppose that I want to create a sitemap after a user visits ./sitemap.xml.

In that case, I would create a function such as:

javascript
if(window.location.href.endsWith('sitemap.xml')){

    const xmlStr = (
        `<?xml version="1.0" encoding="UTF-8"?>
            <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
                <url><loc>https://erikmartinjordan.com</loc></url>
            </urlset>
        `
    );

    window.document.write(xmlStr);

}

If I execute it, the function will render the xml content, but it won't be formatted as an xml tree.

This is because content-type is text/html (default value if we are displaying HTML content). The problem is that there is no way of changing this attribute from the client-side.

At this point, there are 2 options:

1. Sending an xml response from the server:

javascript
response.set('Content-Type', 'text/xml');

2. Using blob to generate a new file:

javascript
if(window.location.href.endsWith('sitemap.xml')){

    const xmlStr = (
        `<?xml version="1.0" encoding="UTF-8"?>
            <urlset xmlns="http://www.sitemaps.org/schemas/sitemap/0.9">
                <url><loc>https://erikmartinjordan.com</loc></url>
            </urlset>
        `
    );
    
    let blob = new Blob([xmlStr], {type: "text/xml"});
    let url = URL.createObjectURL(blob);
    window.open(url, "_self");
    URL.revokeObjectURL(url);
    
}

Both options aren't optimal, since I want to serve the sitemap from the client without any redirections.

The second option seems better than the first one though, but if I use it to generate an xml, Google Search Console won't recognize it and you'll get the following error:

Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.

In conclusion, the only option is to generate an xml file from the server.