gistfile1.js

(function () {
    var el = document.createElement('div'),
        b = document.getElementsByTagName('body')[0],
        otherlib = false;

    // Message window element
    el.style.position = 'fixed';
    el.style.height = '32px';
    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';

    // Determine if jQuery is loaded and/or if another function is already bound to $
    if (typeof jQuery != 'undefined')
        return showMsg('This page already using jQuery v' + jQuery.fn.jquery);
    else if (typeof $ == 'function')
        otherlib = true;

    // Script loader - more or less stolen form jquery core and adapted by paul irish
    function loadScript(url, success) {
        var script = document.createElement('script');
        script.src = url;
        var head = document.getElementsByTagName('head')[0],
        done = false;

        // Attach handlers for all browsers
        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);
    }

    // Load jQuery
    loadScript('http://code.jquery.com/jquery-latest.min.js', function () {
        if (typeof jQuery == 'undefined')
            showMsg('Sorry, but jQuery wasn\'t able to load');
        else
            showMsg('This page is now jQuerified with v' + jQuery.fn.jquery + (otherlib ? ' and noConflict(). Use $jq(), not $().' : ''));
    });

    // Show status message
    function showMsg(msg) {
        el.innerHTML = msg;
        b.appendChild(el);

        window.setTimeout(function () {
            if (typeof jQuery == 'undefined') {
                b.removeChild(el);
            } else {
                jQuery(el).fadeOut('slow', function () {
                    jQuery(this).remove();
                });

                if (otherlib) 
                    $jq = jQuery.noConflict();
            }
        }, 2500);
    }
})();