Cancel Button for service portal - is populating this error while saving the widget

[Sonia22]

 Hi everyone,

Please help me out to add cancel button to end user on the record producer of custom application. I've tried with the following widget code but unfortunately I'm getting following error as "client controller must contains the javascript function, see default value for example." As I'm new to portal please help me out on this widget creation. Kindly refer the attached screenshots. This requirement is a bit urgent. Please any leads are welcome.

Thank you in advance.