url-checker.js

    /**
     * The utility function to append JavaScript for script tag hack.
     *
     * @method _appendScript
     * @param url {String} The JavaScript URL.
     * @param loadHandler {Event} The onload event handler (optional).
     * @return {HTMLElement} The script element.
     */
    _appendScript = function (url, loadHandler) {
        loadHandler = loadHandler || null;
        var scriptEl   = document.createElement("script");
        scriptEl.src   = url;
        scriptEl.async = true;
        document.body.appendChild(scriptEl);
        if (loadHandler) {
            scriptEl.onload = loadHandler;
        }
        return scriptEl;
    }