If Nashorn evaluates a script that only contains function declarations it returns the last declared function as return value. This is against ECMAScript 5.1 section 14 which says that evaluation of a function declaration should not return a value.

http://es5.github.io/#x14

We probably introduced this behaviour because Rhino has the same bug, and people have been using this to obtain a reference to a function evaluated in a script.

One possible way to fix this while still allowing functions to be returned from script evaluation is to only return anonymous function statements (a Nashorn extension).