Var Feedback = feedback;

First off. 'var' is lowercase. Might this be your problem?

If the variable is in the library, that is at Global Scope which is the parent of Activity Scope which is the parent of Page scope which is the parent of Button/Local Scope. The Dev Guide does not explicitly mention JavaScript 'Global Scope' but that is where libraries are loaded.

So, yes, the variable should be visible if you don't have syntax errors.

Note that in the Activity in question, you must also check the box to 'include' your library under the ProntoScript Libraries tab of the Activity Properties.

Note that if you added your library to the System Activity, you must check the box to include it there or within your Activity, you must call System.include(nameofyourjsfile).

Please have a look at Chapter 6 of the Dev Guide and Section 4.3 Variable Scope of the Flanagan 5th Edition book (You can likely find the PDF online via a google search).