1、Uncaught TypeError: Cannot read property ‘dom’ of null
原因：如果代码段没有放入Ext.onReady中
2、Uncaught TypeError: Cannot call method 'hasOwnProperty' of undefined
参考这篇文章：Extjs4---Uncaught TypeError: Cannot call method 'hasOwnProperty' of undefined
3、Cannot read property 'addCls' of null
参考文章：Extjs4---Cannot read property 'addCls' of null
4、Uncaught TypeError: Cannot call method 'substring' of undefined
参考文章：Extjs4---Uncaught TypeError: Cannot call method 'substring' of undefined