Librarify: A bookmarklet that injects JavaScript libaries into any page. Based on Rey Bango's jQuerify: http://blog.reybango.com/2010/09/02/how-to-easily-inject-jquery-into-any-web-page/

Librarify.js

// Librarify: A bookmarklet that injects JavaScript libaries into any page.
// Based on Rey Bango's jQuerify: http://blog.reybango.com/2010/09/02/how-to-easily-inject-jquery-into-any-web-page/

javascript: (function (libname) {
    var
        libraries = {
            jquery: {
                url: '//ajax.googleapis.com/ajax/libs/jquery/1/jquery.min.js',
                libvar: '$'
            },
            underscore: {
                url: '//cdnjs.cloudflare.com/ajax/libs/underscore.js/1.4.4/underscore-min.js',
                libvar: '_'
            }
        },
        library = libraries[libname.toLowerCase()],
        showMessage = function (message) {
            var
                messageElem = document.createElement('div'),
                body = document.getElementsByTagName('body')[0];
            messageElem.style.position = 'fixed';
            messageElem.style.width = '400px';
            messageElem.style.marginLeft = '-200px';
            messageElem.style.top = '0';
            messageElem.style.left = '50%';
            messageElem.style.padding = '10px';
            messageElem.style.zIndex = 1001;
            messageElem.style.fontSize = '12pt';
            messageElem.style.color = '#222';
            messageElem.style.backgroundColor = '#f99';
            messageElem.innerHTML = message;
            body.appendChild(messageElem);
            window.setTimeout(function () {
                body.removeChild(messageElem);
            }, 2500);
        },
        getScript = function (url, success) {
            var script = document.createElement('script'),
                head = document.getElementsByTagName('head')[0],
                done = false;
            script.src = url;
            script.onload = script.onreadystatechange = function () {
                if (
                    !done &&
                    (!this.readyState || this.readyState === 'loaded' ||
                    this.readyState === 'complete')
                ) {
                    done = true;
                    success();
                }
            };
            head.appendChild(script);
        };
    if (!library) {
        library = {
            url: libname
        }
    }
    getScript(library.url, function () {
        var message;
        if (library.libvar && typeof window[library.libvar] === 'undefined') {
            message = 'Sorry, but ' + libname + ' wasn\'t able to load';
        } else {
            message = 'This page is now loaded with ' + libname;
        }
        return showMessage(message);
    });
})('%s');