$.getscript returning 'undefined'

I am trying to get the script found under 'Enforce Drag and Drop documents to apply metadata' to work and I am always getting an 'Undefined' error here:

$.getScript("path_to_my_custom_js_file/DragDrop.Extended.js");

I have tried several different locations and ways to write the URL but it always comes back with the same error. Any help will be appreciated, thanks.