点击显示也隐藏 和 点击空白处隐藏

    $(\'.menu ul li:nth-of-type(4)\').click(function(event){
        if($(".menu_bg").is(":visible")){
            $(\'.menu_bg\').hide();
            $(\'.menu ul li:nth-of-type(4)>a\').text(\'案例+\');
            $(document).one("click",function(){
                $(\'.menu_bg\').show();
                $(\'.menu ul li:nth-of-type(4)>a\').text(\'案例-\');
            });
        }else{
            $(\'.menu_bg\').show();
            $(\'.menu ul li:nth-of-type(4)>a\').text(\'案例-\');
            $(document).one("click",function(){
                $(\'.menu_bg\').hide();
                $(\'.menu ul li:nth-of-type(4)>a\').text(\'案例+\');
            });
        }
        event.stopPropagation();
    });
    $("#menu_bg").click(function (event) {
        event.stopPropagation();//在Div区域内的点击事件阻止冒泡到document
    });