ExtJS4.1 : Uncaught TypeError: Cannot call method 'getWidth' of undefined

I created a formpanel, which has a predefined width and height:

var myCrearUsuarioFormPanel = Ext.create('WebMonitorClass.view.CrearUsuarioFormPanel');

Know I needed to put my myCrearUsuarioFormPanel into a window. I needed to set the window width and height the same as the myCrearUsuarioFormPanel width and height:
                         
                            var myWindow = Ext.create("Ext.Window",{
                                width : myCrearUsuarioFormPanel.getWidth() //  here I tried that
                                ,height: myCrearUsuarioFormPanel.getHeight() // here I tried that
                                ,title : 'Crear Usuario'                                
                                ,layout: 'absolute'
                                ,closable : false                                
                                ,items:[myCrearUsuarioFormPanel]
                            }).show();

But I Got:

Uncaught TypeError: Cannot call method 'getWidth' of undefined 

in this line

width : myCrearUsuarioFormPanel.getWidth()

The solution is to use the offsetWidth and offsetHeight properties:


                          var myWindow = Ext.create("Ext.Window",{
                                width : myCrearUsuarioFormPanel.offsetWidth // Here is the solution
                                ,height: myCrearUsuarioFormPanel.offsetHeight // Here is the solution
                                ,title : 'Crear Usuario'                                
                                ,layout: 'absolute'
                                ,closable : false                                
                                ,items:[myCrearUsuarioFormPanel]
                            }).show();

Resource:
http://stackoverflow.com/questions/5249723/wrong-div-width-when-getting-it-with-javascript
http://stackoverflow.com/questions/10634282/in-extjs-when-dragdrop-offsetwidth-is-null-or-not-an-object-error-for-ie7