关于MUI示例侧滑导航中父子模板实例应用问题

加载以后 按返回键 然后就报错了 按左上缴的返回按钮的话一切正常
Uncaught TypeError: Cannot call method 'loadURL' of undefined at index.html:150
Uncaught TypeError: Cannot call method 'loadURL' of undefined at index.html:150
Uncaught TypeError: Cannot call method 'getURL' of undefined
求解~