exes-and-ohs.js

function XO(str = []) {
  let amount_x = [],
    amount_o = [];
  for (let i of str.toString()) {
    if (i.toLocaleLowerCase() == "x") {
      amount_x.push(i);
    }
    if (i.toLocaleLowerCase() == "o") {
      amount_o.push(i);
    }
  }
  return amount_o.length === amount_x.length ? true : false;
}

console.log(XO("ooxXm"));
console.log(XO("zpzpzpp"));
console.log(XO("zzoo"));