Dynamically load jquery if not present

With this code you can retrieve if jquery is set in your script, if jquery is not set then the script load it dinamically and set it. 

(function () {
    var jQuery;

    if (window.jQuery === undefined || window.jQuery.fn.jquery !== '1.4.2') {
        var script_tag = document.createElement('script');
        script_tag.setAttribute("type", "text/javascript");
        script_tag.setAttribute("src", pathWidget + "/scripts/jquery-1.7.min.js");

        if (script_tag.readyState) {
            script_tag.onreadystatechange = function () { // For old versions of IE
                if (this.readyState == 'complete' || this.readyState == 'loaded') {
                    scriptLoadHandler();
                }
            };
        } else {
            script_tag.onload = scriptLoadHandler;
        }
        (document.getElementsByTagName("head")[0] || document.documentElement).appendChild(script_tag);
    } else {
        jQuery = window.jQuery;
        main();
    }

    function scriptLoadHandler() {
        jQuery = window.jQuery.noConflict(true);
        main();
    }

    function main() {
        jQuery(document).ready(function ($) {

        });
    }
})();