javascript: (function() {

    var url = prompt('URL of script to inject:', 'https://code.jquery.com/jquery-3.4.1.min.js');

    if (url) {

        console.log('Script inject request URL:', url);

        var script = document.createElement('script');
        script.src = url;
        document.getElementsByTagName('head')[0].appendChild(script);

        console.log('Injected script: ', script);
    }

})();