为什么下面的jquery没有启动？每次都会转到“else”。

if ( is_admin() && $pagenow == \'theme-install.php\' && $_GET[\'tab\']=="upload"){
    add_action(\'admin_print_scripts\', \'theme_upgrade_alert\');
    function theme_upgrade_alert(){
        wp_enqueue_script(\'jquery\');
        echo \'
        <script type="text/javascript">
        if(typeof jQuery!="undefined"){
            jQuery.noConflict();
            //jQuery(document).ready(function(){
                jQuery(".install-help").hide();
            //});
        }
        else
        {
            alert("If you are attempting to upgrade the current theme, you must do it via theme options.");
        }
        </script>\';
        }
}