Wtf

let arrNum = [],
    arr = [],
    n = Math.round(Math.random() * 10);
    n % 2 === 1 ? n += 1: n = n;

for(let i = 0; i < n; i++) {
    arrNum[i] = i;
    let a = Math.round(Math.random() * 10);
    a = -a;
    arr[i] = a;
};

console.log(arr);
console.log(arrNum);

n = n / 2;
console.log(n);

for(let i = 0; i < n; i++) {
    let b = Math.round(Math.random() * n),
        c = Math.round(Math.random() * 1000);
    arr[b] = c;
    arrNum = arrNum.filter(item => item != b);
};

console.log(arr);
console.log(arrNum);