Extjs中如何关闭parent对象窗口打开的window对象

有a,b两个页面，a页面为主页面，有按钮一个，点击按钮弹出一个windows对象，在其中显示b页面。b页面中也有一个按钮，点击关闭窗口。
a.htm (部分代码)

 

<script type="text/javascript"> function openWindow(id,title,url,width,height){     var win = Ext.get(id)     if (win) {         win.close();         return;     }     win = new Ext.Window({         id:id,         title:title,         layout:'fit',         width:width,         height:height,         closeAction:'close',         collapsible:true,         plain: false,         resizable: true,         html : '+</span>url<span style="color:#0000cc;">+</span><span style="color:#ff00ff;">'">'     });     win.show(); } function myfunction(){     openWindow('b-win','窗口中打开b页面','b.htm',400,300); } </script> <input type="button" name="button1" value="打开窗口" onClick="myfunction()">

b.htm（部分代码）

<script type="text/javascript"> function closewin(){     var win = parent.Ext.getCmp('b-win');     if (win) {win.close();} } </script> <input type="button" name="button1" value="关闭a打开的窗口" onClick="closewin()">