Recursive functions like this are more like closures and not pure functions. Aliasing factorial1 and reassigning it will break the recursion [1]. Maybe this is

Recursive functions like this are more like closures and not pure functions. Aliasing factorial1 and reassigning it will break the recursion [1]. Maybe this is what jbrooksuk was referring to. [1] https://leanpub.com/javascript-allonge/read#recursive https://leanpub.com/javascript-allonge/read#recursive