Loads jQuery if not loaded

gistfile1.js

(function() {
    var $;

    if (window.jQuery === undefined || window.jQuery.fn.jquery < '1.5') {
        (function(d, t) {
            var js = document.createElement(t);
            js.src = location.protocol + '//ajax.googleapis.com/ajax/libs/jquery/1.5.1/jquery.min.js';
            js.onload = scriptLoadHandler;
            js.onreadystatechange = function() {
                if (this.readyState == 'complete' || this.readyState == 'loaded') {
                    scriptLoadHandler();
                }
            };
            (d.getElementsByTagName('head')[0] || d.documentElement).appendChild(js);
        }(document, 'script'));
    } else {
        $ = window.jQuery;
        foo();
    }

    var scriptLoadHandler = function() {
        $ = window.jQuery.noConflict(true);
        foo();
    };

    var foo = function() {
        // jQuery is ready here for your pleasure
    };
})();