Problems with sitefinity feather

Hello, i was doing the sitefinity hello world widget with feather in sitefinity 9.0. I don't know why isn't working. When access to a sitefinity page to use the widget.. return and error of "Undefined" and if i try to delete a page..also shows and error(see above image). Some one can help me?

Hello,

Here is a video demonstrating how to create a simple Sitefinity MVC Hello World Widget;

http://www.sitefinity.com/developer-network/videos/sitefinity-mvc-hello-world-widget

and a direct documentation link on how to 
Create MVC-based Sitefinity widgets
http://docs.sitefinity.com/for-developers-create-mvc-based-sitefinity-widgets

Regarding your screenshot with the error, I do not see the relevance to the issue or where this could come from.

Please observe the demo video and the documentation as mentioned above.

I hope the above information helps. Otherwise please provide the steps you took to accomplish this.