Ext.ComponentManager

// Create an Ext.Window and provide it with an id of 'myWin'
var a = new Ext.Window({
  id: 'myWin',
  width: 400,
  height: 400,
  closeAction: 'hide',
  html: 'Sample content for a demo'
});
a.show();

// retrieve myWin
Ext.getCmp('myWin').hide();