What's wrong with the Phonegap app code?

Question

JavaScript

Here is the actual link to the entire js code:
https://jsfiddle.net/edward96/67qn0nr2/
in reader.onloadend = function(e) there is a line fileName = slice_file(reader.result); .So fileName is a global variable, but for some reason the value is assigned locally, it is visible in alert , and when I then use the value of this variable, it stands as undefined. Why is this happening and how to fix / bypass / replace it, in general, what would have worked :).