I would like to give some feedback about ...
do not manipulate original array, but why display [null,null,null,null]??
From: https://js.checkio.org/mission/non-unique-elements/solve/
HTTP_USER_AGENT:
Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/52.0.2743.116 Safari/537.36
Created at: 2016/12/27 09:48; Updated at: 2016/12/27 09:48
