Safely loading JS libraries (jQuery)

Safely loading JS libraries (jQuery).js

function loadScript(address, callback) {
        var script_tag = document.createElement('script');
        script_tag.setAttribute("type", "text/javascript");
        script_tag.setAttribute("src", address);
        if (script_tag.readyState) {
            script_tag.onreadystatechange = function () { // For old versions of IE
                if (this.readyState == 'complete' || this.readyState == 'loaded') {
                    callback();
                }
            };
        } else { // Other browsers
            script_tag.onload = callback;
        }
        // Try to find the head, otherwise default to the documentElement
        (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag);
    }

    function scriptLoadHandler() {
        root._myNS.widget = new widget();
        root._myNS.widget.render();
        console.log('Widget $ is on version: ' + root._myNS.$.fn.jquery);
        console.log('Page $ is on version: ' + $.fn.jquery);
    }

    function load() {
        // version of jQuery check
        if (!root._myNS.$ || !root._myNS.$.fn || !root._myNS.$.fn.jquery || root._myNS.$.fn.jquery !== '1.11.1') {
            //load jquery we need
            loadScript('http://code.jquery.com/jquery-1.11.1.min.js', function () {
                root._myNS.$ = window.jQuery.noConflict(true); // set our widget library to the newly loaded version
                loadScript(urlRoot + 'js/widget.js', scriptLoadHandler);
            });
        } else {
            //skip jquery and just load widget
            loadScript(urlRoot + 'js/widget.js', scriptLoadHandler);
        }
    }