Changing website favicon dynamically

You can simply:
  1. Include the script `update_favicon.js`
  2. Call function set_favicon with a plain URL
Example in head: 
        <link rel="icon" type="image/x-icon" href="./favicon.ico">

        <script src="update_favicon.js"></script>
        <script>
            set_favicon( 'https://stackoverflow.com/favicon.ico' ); // Using URL
        </script>