Another option is:<BR><BR>A .js file which is an inelegant solution but is vanilla-html-workable.<BR><BR>And then you can go to ASP or PHP but those are way over the top for what you need.

How to Use Index.Php Instead of Index.Html. The PHP engine lets you create dynamic Web pages. PHP also reads HTML, so you can save an HTML file with a PHP extension and upload the new file to your ...