1.) You need to take into account zeros. In JavaScript you can have -0 (for some reason), even though zero is neither positive or negative and therefore shouldn't have a sign. Your code ignores zeros so that it will invert a zero from "0" to "-0". You must make it so that it doesn't invert the zeroes (no negative sign).

2.) You're not meant to modify the original array. It's bad practise to modify it because it will change it permenantly and you can't reverse the process. You can either duplicate the array, see here: http://stackoverflow.com/questions/3978492/javascript-fastest-way-to-duplicate-an-array-slice-vs-for-loop or you can create a new array and append to that. Here is an example why you shouldn't modify the array:

Apologies for the delay, I didn't see your message.

May you post your code as a reply to this comment, so that I can help you? Put your code between two sets of three backticks to format it properly in Markdown, see here: https://github.com/adam-p/markdown-here/wiki/Markdown-Cheatsheet#code.