Array element parity.js

/*
Description:
In this Kata, you will be given an array of integers whose elements have both a negative and a positive value, except for one integer that is either only negative or only positive. Your task will be to find that integer.

For example,

solve[1,-1,2,-2,3] = 3  --> 3 only has a positive ocurrence.
solve([-3,1,2,3,-1,-4,-2]) = -4  --> -4 only has a negative occurence
solve([1,-1,2,-2,3,3]) = 3  --> the integer that is only positive or only negative my appear more than once.
Good luck!
*/
function solve(arr){
  return arr.filter(a=>arr.indexOf(-a)===-1)[0];  
};