If I want to realize the function of picture, what should I do?

I need some help~~
This is the example in the document,

This is my code.

And I want to know, why the row range [-1..-1] can't use in my code, even the label"diff" does not show in the Windowing.
Row range[..-1] [..-2] [-2..-1] can't use too.

I want to know is that my code wrong? But why the example  can run?
 

I want to show the reuslt with the percentage, what should I do?

This is my custom object method,I use it to update my list; 
I also write a js code under the button.  But when I done the js code, the page can jump,but my custom metod is not execute.
I want ask how should I can execute the custom object method,and also execute the js method.
  Thin

I want to show the reuslt with the percentage, what should I do?

This is my custom object method,I use it to update my list; 
I also write a js code under the button.  But when I done the js code, the page can jump,but my custom metod is not execute.
I want ask how should I can execute the custom object method,and also execute the js method.
  Thin