新建子窗口偶尔卡死

代码如下：

  document.on("click", "#buy", function (evt, button) {     
            jj.print("购买页面");       
            var butWindow = Window.this.modal({
                parent: Window.this,
                url: "/sc/buy/",
                parameters: { parametJJ: jj },
                 //state: Window.WINDOW_MODAL ,
            });           
        });

有时候关闭页面几次，再重新点按钮就不会创建窗口了，解决办法，使用如下代码创建：

 //购买软件
        document.on("click", "#buy", function (evt, button) {                   
            if(wndBuy == undefined){
                //创建子窗口
                wndBuy = new Window({ 
                    url   : "/sc/buy/", 
                    state : Window.WINDOW_MODAL,
                    parent: Window.this,
                    parameters: { parametJJ: jj },
                    alignment: 5, // in the center of screen
                } );

                //子窗口要关闭
                wndBuy.on("closerequest", event => {
                    jj.print("子窗口请求关闭",event.reason);
                    wndBuy = undefined;                                
                });               
            }
                 
        });