Underscorify puts underscore on the current page (based on jQuerify http://www.learningjquery.com/2009/04/better-stronger-safer-jquerify-bookmarklet)

bookmarklet.js

javascript:!function(){function e(e,t){var n=document.createElement("script");n.src=e;var o=document.getElementsByTagName("head")[0],i=!1;n.onload=n.onreadystatechange=function(){i||this.readyState&&"loaded"!=this.readyState&&"complete"!=this.readyState||(i=!0,t(),n.onload=n.onreadystatechange=null,o.removeChild(n))},o.appendChild(n)}function t(){n.innerHTML=d,o.appendChild(n),n.style.opacity=1,"undefined"==typeof _?o.removeChild(n):setTimeout(function(){n.style.opacity=0,n.style.transition="4s 3s",n.addEventListener("transitionend",function(){o.removeChild(n)}),n.addEventListener("webkitTransitionEnd",function(){o.removeChild(n)}),i&&(underscore=_.noConflict())},500)}var n=document.createElement("div"),o=document.getElementsByTagName("body")[0],i=!1,d="";return n.style.position="fixed",n.style.height="36px",n.style.width="220px",n.style.marginLeft="-110px",n.style.top="0",n.style.left="50%",n.style.padding="5px 10px",n.style.zIndex=1001,n.style.fontSize="12px",n.style.color="#222",n.style.backgroundColor="#f99","undefined"!=typeof _?(d="This page already using underscore v"+_.VERSION,t()):("function"==typeof _&&(i=!0),e("https://rawgit.com/jashkenas/underscore/master/underscore.js",function(){return"undefined"==typeof _?d="Sorry, but underscore wasn't able to load":(d="This page is now underscorified with v"+_.VERSION,i&&(d+=" and noConflict(). Use underscore, not _.")),t()}),void 0)}()

source.js

(function() {
    var el = document.createElement('div'),
        b = document.getElementsByTagName('body')[0]
        , otherlib = false, msg = '';
    el.style.position = 'fixed';
    el.style.height = '36px';
    el.style.width = '220px';
    el.style.marginLeft = '-110px';
    el.style.top = '0';
    el.style.left = '50%';
    el.style.padding = '5px 10px';
    el.style.zIndex = 1001;
    el.style.fontSize = '12px';
    el.style.color = '#222';
    el.style.backgroundColor = '#f99';
    if (typeof _ != 'undefined') {
        msg = 'This page already using underscore v' + _.VERSION;
        return showMsg();
    } else if (typeof _ == 'function') {
        otherlib = true;
    }

    function getScript(url, success) {
        var script = document.createElement('script');
        script.src = url;
        var head = document.getElementsByTagName('head')[0],
            done = false;
        script.onload = script.onreadystatechange = function() {
            if (!done && (!this.readyState || this.readyState == 'loaded' || this.readyState == 'complete')) {
                done = true;
                success();
                script.onload = script.onreadystatechange = null;
                head.removeChild(script);
            }
        };
        head.appendChild(script);
    }
    getScript('https://rawgit.com/jashkenas/underscore/master/underscore.js', function() {
        if (typeof _ == 'undefined') {
            msg = 'Sorry, but underscore wasn\'t able to load';
        } else {
            msg = 'This page is now underscorified with v' + _.VERSION;
            if (otherlib) {
                msg += ' and noConflict(). Use underscore, not _.';
            }
        }
        return showMsg();
    });

    function showMsg() {
        el.innerHTML = msg;
        b.appendChild(el);
        el.style.opacity = 1
        if (typeof _ == 'undefined') {
            b.removeChild(el);
        } else {
            setTimeout(function() {
                el.style.opacity = 0
                el.style.transition = '4s 3s'
                el.addEventListener('transitionend', function() {
                  b.removeChild(el)
                })
                el.addEventListener('webkitTransitionEnd', function() {
                  b.removeChild(el)
                })
                if (otherlib) {
                    underscore = _.noConflict();
                }
            }, 500)
        }
    }
})();